CBSE Class 9

These NCERT Solutions for Class 9 Maths Chapter 1 Number Systems Ex 1.2 Questions and Answers are prepared by our highly skilled subject experts.

NCERT Solutions for Class 9 Maths Chapter 1 Number Systems Exercise 1.2

Question 1.
State whether the following statements are true or false. Justify your answer.
(i) Every irrational number is a real number.
(ii) Every point on the number line is of the form √m where m is a natural number.
(iii) Every real number is an irrational number.
Solution:
(i) True, because the set of every rational and every irrational number is called real number.
(ii) False, no negative number can be the square root of any natural number.
(iii) False, because a real number is the set of every irrational and rationed number. For example, 2 is real but not irrational.

Question 2.
Are the square roots of all positive integers irrational? If not give an example of the square root of a number that is a rational number.
Solution:
No, the square roots of all positive integers are not always irrational.
For e.g. 4 is a positive integer and the value of their square root is 2. Which is a rational number.

Question 3.
Show how √5 can be represented on the number line.
Solution:
To represent √5 on the number line, taking O at zero on the number line.
Again taking OA = 2 unit in the positive direction of the number line.
Again draw BA ⊥ OA and the length of BA = 1 unit.
Join BO and complete a right-angle ∆OAB.
Now, the length of BO = √5 (by Pythagoras theorem).
Again we take OB as a radius and draw a circle which cuts the number line at C.
Therefore, the length of OC is also equal to √5.
Hence point C is the required point on the number line.

Question 4.
Classroom activity (Constructing the ‘square root spiral’).
Take a large sheet of paper and construct the ‘square spiral’ in the following fashion. Start with a point O and draw a line segment P₁P₂ perpendicular to OP₁ of unit length (see Fig. 1.2). Now draw a line segment P₂P₃ perpendicular to OP₂. Then draw a line segment P₃P₄ perpendicular to OP₃. Continuing in this manner, you can get the line segment P_n-1P_n by drawing a line segment of unit length perpendicular to OP_n-1. In this manner, you will have created the points P₂, P₃…, P_n…, and joined them to create a beautiful spiral depicting √2, √3, √4……

Fig. Constructing square root spiral.
Solution:
For self-practice.

These NCERT Solutions for Class 9 Maths Chapter 1 Number Systems Ex 1.1 Questions and Answers are prepared by our highly skilled subject experts.

NCERT Solutions for Class 9 Maths Chapter 1 Number Systems Exercise 1.1

Question 1.
Is zero a rational number? Can you write it in the form \(\frac{p}{q}\), where p and q are integers and q ≠ 0?
Solution:
Yes, zero is a rational number. Because, \(\frac{0}{i}\) is also equal to zero. Where is integer. Zero is also represented by \(\frac{0}{1}\), which is in the form of \(\frac{p}{q}\), where p and q both are integers and q ≠ 0.

Question 2.
Find six rational numbers between 3 and 4.
Solution:
To find six rational number between 3 and 4, we take 3 and 4 as a rational number with denominator 6 + 1 = 7, i.e.
3 = \(\frac{21}{7}\) and 4 = \(\frac{28}{7}\)
Then required six rational number between 3 and 4 are
\(\frac{22}{7}, \frac{23}{7}, \frac{24}{7}, \frac{25}{7}, \frac{26}{7} \text { and } \frac{27}{7}\)

Question 3.
Find five rational numbers between \(\frac{3}{5}\) and \(\frac{4}{5}\).
Solution:
To find five rational numbers between \(\frac{3}{5}\) and \(\frac{4}{5}\), we take \(\frac{3}{5}\) and \(\frac{4}{5}\) as a rational number with denominator 30.
i.e. \(\frac{3}{5}=\frac{3}{5} \times \frac{6}{6}=\frac{18}{30}\) and \(\frac{4}{5}=\frac{4}{5} \times \frac{6}{6}=\frac{24}{30}\)
Then, required six rational numbers between \(\frac{3}{5}\) and \(\frac{4}{5}\) are
\(\frac{19}{30}, \frac{20}{30}, \frac{21}{30}, \frac{22}{30} \text { and } \frac{23}{30}\)

Question 4.
State whether the following statements are true or false? Give a reason for your answer.
(i) Every natural number is a whole number.
(ii) Every integer is a whole number.
(iii) Every rational number is a whole number.
Solution:
(i) True, because numbers 1, 2, 3, 4, 5, ………. is a natural number and whole number is 0, 1, 2, 3, 4, 5, ………
(ii) False, because -1 is an integer but it is not a whole number.
(iii) False, because \(\frac{1}{2}\) is a rational number but it is not a whole number.

These NCERT Solutions for Class 9 Science Chapter 15 Improvement in Food Resources Questions and Answers are prepared by our highly skilled subject experts to help students while preparing for their exams.

Improvement in Food Resources NCERT Solutions for Class 9 Science Chapter 15

Class 9 Science Chapter 15 Improvement in Food Resources InText Questions and Answers

Question 1.
What do we get from cereals, pulses, fruits and vegetables?
Answer:

• Cereals provide us with carbohydrates. Also, they are a rich source of energy.
• Pulses give us proteins.
• Fruits and vegetables are a rich source of vitamins and minerals. A small amount of proteins, carbohydrates, and fats are also present in them.

Question 2.
How do biotic and abiotic factors affect crop production?
Answer:
A variety of biotic factors such as pests, nematodes, diseases, etc. can reduce net crop production. A pest causes damage to agriculture by feeding on crops. For example, boll weevil is a pest on cotton. It attacks the cotton crop, thereby reducing its yield. Weeds also reduce crop productivity by competing with the main crop for nutrients, light, and space.

Similarly, abiotic factors such as salinity, temperature, etc. affect the net crop production. Some natural calamities such as droughts and floods are unpredictable. Their occurrence has a great impact on crops sometimes, destroying the entire crop.

Question 3.
What are the desirable agronomic characteristics for crop improvements?
Answer:
The desirable agronomic characteristics for crop improvements are:

• Tallness and profuse branching in any fodder crop.
• Dwarfness in cereals.

These desirable agronomic characteristics help in increasing crop productivity.

Question 4.
What are macro-nutrients and why are they called macro-nutrients?
Answer:
Macro-nutrients are nutrients required in relatively large quantities for growth and development of plants. They are six in number. Since they are required in large quantities, they are known as macro-nutrient. The six macronutrients required by plants are nitrogen, phosphorus, potassium, calcium, magnesium, and sulphur.

Question 5.
How do plants get nutrients?
Answer:
Plants require sixteen essential nutrients from nature for their growth and development. All these nutrients are obtained from air, water, and soil. Soil is the major source of nutrients. Thirteen of these nutrients are available from soil. The remaining three nutrients
(carbon, oxygen, and hydrogen) are obtained from air and water.

Question 6.
Compare the use of manure and fertilizers in maintaining soil fertility.
Answer:
Manures increase soil fertility by enriching the soil with organic matter and nutrients as it is prepared by the decomposition of animal excreta and plant wastes. On the other hand, fertilizers are mostly inorganic compounds whose excessive use is harmful to the symbiotic micro-organisms living in soil. Their excessive use also reduces soil fertility. Hence, fertilizers are considered good for only short term use.

Question 7.
Which of the following conditions will give the most benefits? Why?
(a) Farmers use high-quality seeds, do not adopt irrigation or use fertilizers.
(b) Farmers use ordinary seeds, adopt irrigation and use fertilizer.
(c) Farmers use quality seeds, adopt irrigation, use fertilizer and use crop protection measures.
Answer:
(c) Farmers using good quality seeds, adopting irrigation, using fertilizers, and using crop protection measures will derive most benefits.

• The use of good quality seeds increases the total crop production. If a farmer is using good quality seeds, then a majority of the seeds will germinate properly, and will grow into a healthy plant.
• Proper irrigation methods improve the water availability to crops.
• Fertilizers ensure healthy growth and development in plants by providing the essential nutrients such as nitrogen, phosphorus, potassium, etc.
• Crop protection measures include various methods to control weeds, pests, and infectious agents. If all these necessary measures are taken by a farmer, then the overall production of crops will increase.

Question 8.
Why should preventive measures and biological control methods be preferred for protecting crops?
Answer:
Preventive measures and biological control methods should be preferred for protecting crops because excessive use of chemicals leads to environmental problems. These chemicals are also poisonous for plants and animals. Preventive measures include proper soil and seed preparation, timely sowing of seeds, intercropping and mixed cropping, usage of resistant varieties of crops, etc.

On the other hand, biological control methods include the usage of bio-pesticides that are less toxic for the environment. An example of bio-pesticides is Bacillus thuringenesis, which is an insect pathogen that kills a wide range of insect larvae. Therefore, both preventive measures and biological control methods are considered eco-friendly methods of crop protection.

Question 9.
What factors may be responsible for losses of grains during storage?
Answer:
During the storage of grains, various biotic factors such as insects, rodents, mites, fungi, bacteria, etc. and various abiotic factors such as inappropriate moisture, temperature, lack of sunlight, flood, etc. are responsible for losses of grains. These factors act on stored grains and result in degradation, poor germinability, discolouration, etc.

Question 10.
Which method is commonly used for improving cattle breeds and why?
Answer:
Cattle farming is commonly used for improving cattle breeds. The purpose of cattle farming is to increase the production of milk and draught labour for agricultural work. Dairy animals (females) are used for obtaining milk and draught animals (males) are engaged in agricultural fields for labour work such as carting, irrigation, tilling, etc. Crossbreeding between two good varieties of cattle will produce a new improved variety.

For example, the cross between foreign breeds such as Jersey Brown, Swiss (having long lactation periods) and Indian breeds such as Red Sindhi, Sahiwal (having excellent resistance power against diseases) produces a new variety having qualities of both breeds.

Question 11.
What management practices are common in dairy and poultry farming?
Answer:
Common management practices in dairy and poultry farming are:

• Proper shelter facilities and their regular cleaning.
• Some basic hygienic conditions such as clean water, nutritious food, etc.
• Animals are kept in spacious, airy, and ventilated place.
• Prevention and cure of diseases attire right time is ensured.

Question 12.
What are the differences between broilers and layers and in their management?
Answer:
Layers are meant for egg production, whereas broilers are meant for poultry meat. Nutritional, environmental, and housing conditions required by broilers are different from those required by egg layers. A broiler chicken, for their proper growth, requires vitamin rich supplements especially vitamin A and K. Also, their diet includes protein rich food and enough fat. They also require extra care and maintenance to increase their survival rate in comparison to egg layers.

Question 13.
What are the desirable characters of bee varieties suitable for honey production?
Answer:
Bee varieties having the following desirable characters are suitable for honey production:

• They should yield high quantity of honey.
• They should not sting much.
• They should stay in the beehive for long durations. ‘
• They should breed very well.

Question 14.
What is pasturage and how is it related to honey production?
Answer:
Pasturage is the availability of flowers from which bees collect nectar and pollen. It is related to the production of honey as it determines the taste and quantity of honey.

Class 9 Science Chapter 15 Improvement in Food Resources Textbook Questions and Answers

Question 1.
Explain any one method of crop production which ensures high yield.
Answer:
Crop rotation is one of the methods of crop production that ensures high yield. It is the method of growing two or more varieties of crops on the same land in sequential seasons. A crop utilises some particular nutrients in larger quantities from the soil. Then, if the same crop is grown in subsequent seasons those nutrients will get depleted in the soil. Therefore, crops having different nutrient requirements are rotated.

For example, legumes which have nitrogen-fixing bacteria in their root nodules supply the soil with nitrogen. Therefore, these legumes are rotated with nitrogen requiring cereals such as wheat and maize. This method reduces the need of fertilizers, thereby increasing the overall yield of crops.

Question 2.
Why are manures and fertilizers used in fields?
Answer:
Manures and fertilizers are used in A fields to enrich the soil with the required nutrients. Manure helps in enriching the soil with organic matter and nutrients. This improves the fertility and structure of the soil. On the other hand, fertilizers ensure a healthy growth and development in plants. They are a good source of nitrogen, phosphorus, and potassium. To get an optimum yield, it is instructed to use’s balanced combination of manures and fertilizers in the soil.

Question 3.
What are the advantages of inter-cropping and crop rotation?
Answer:
Inter-cropping and crop rotation both play an important role in increasing the yield of crops. Inter-cropping helps in preventing pests and diseases to spread throughout the field. It also increases soil fertility, whereas crop rotation prevents soil depletion, increases soil fertility, and reduces soil erosion. Both these methods reduce the need for fertilizers. It also helps in controlling weeds and controls the growth of pathogens and pests in crops.

Question 4.
What is genetic manipulation? How is it useful in agricultural practices?
Answer:
Genetic manipulation is a process where the gene for a particular character is introduced inside the chromosome of a cell. When the gene for a particular character is introduced in a plant cell, 9 transgenic plant is produced. These transgenic plants exhibit characters governed by the newly introduced gene.

For example, let us assume there is a wild plant that produces small fruits. If the gene responsible for a larger fruit size is introduced in this plant, this plant becomes transgenic, and starts producing larger fruits. Similarly, genes for higher yield, disease resistance, etc. can be introduced in any desired plant.

Therefore, gene manipulation plays an important role in agricultural practices. It helps in improving crop variety. It ensures food security and insect resistant crops. It also improves the quality and yield of Crops.

Question 5.
How do storage grain losses occur?
Answer:
There are various biotic and abiotic factors that act on stored grains and result in degradation, poor germinability, discolouration, etc. Biotic factors include insects or pests that cause direct damage by feeding on seeds. They also deteriorate and contaminate the grain, making it unfit for further consumption.

Abiotic factors such as temperature, light, moisture, etc., also affect the seed. They decrease the germinating ability of the seeds and make them unfit for future use by farmers. Unpredictable occurrence of natural calamities such as droughts and floods also causes destruction of crops.

Question 6.
How do good animal husbandry practices benefit farmers?
Answer:
Cattle farming is one of the methods of animal husbandry that is most beneficial for farmers. Using this method, better breeds of draught animals can be produced. Such draught animals are engaged in agricultural fields for labour work such as carting, irrigation, tilling, etc.

Question 7.
What are the benefits of cattle farming?
Answer:
Benefits of cattle farming:

• Good quality and quantity of milk can be produced.
• Draught labour animals can be produced for agricultural work.
• New variety that are resistant to diseases can be produced by crossing two varieties with the desired traits.

Question 8.
For increasing production, what is common in poultry, fisheries and bee-keeping?
Answer:
The common factor for increasing production in poultry, fisheries, and beekeeping is the proper management techniques that are to be followed. Regular cleaning of farms is of utmost importance. Maintenance of temperature and prevention and cure of diseases is also required to increase the number of animals.

Question 9.
How do you differentiate between capture fishing, mariculture and aquaculture?
Answer:
Capture fishing involves the fishing or capturing of fishes from natural water reservoirs using fishing liner or fishing nets. A different varieties of the fishes are ended up being captured in the processes, some are edible while others are not being very young or inedible type hence, disturb the aquatic ecosystem.

Mariculture involves the culturing of fishes in fresh water and brackish water It also involves the culturing for sea food.

Aquaculture involves the culturing of inland fisheries and marine fisheries in which different type of edible fishes are reared and cultured in the artificially made ponds. It also involves the culturing of other aquatic animals like mussels, prawns, oysters, snails for pearls, etc.

Class 9 Science Chapter 15 Improvement in Food Resources Additional Important Questions and Answers

Multiple Choice Question
Choose the correct option:

Question 1.
Which one is an oil yielding plant among the following?
(a) Lentil
(b) Sunflower
(c) Cauliflower
(d) Hibiscus
Answer:
(b) Sunflower

Question 2.
Which one is not a source of carbohydrate?
(a) Rice
(b) Millets
(c) Sorghum
(d) Gram
Answer:
(d) Gram

Question 3.
Find out the wrong statement from the following
(a) White revolution is meant for increase in milk production
(b) Blue revolution is meant for increase in fish production
(c) Increasing food production without compromising with environmental quality is called as sustainable agriculture
(d) None of the above
Answer:
(d) None of the above

Question 4.
To solve the food problem of the country, which among the following is necessary?
(a) Increased production and storage of food grains
(b) Easy access of people to the food grain
(c) People should have money to purchase the grains
(d) All of the above
Answer:
(d) All of the above

Question 5.
Find out the correct sentence
(i) Hybridisation means crossing between genetically dissimilar plants
(ii) Cross between two varieties is called as interspecific hybridisation
(iii) Introducing genes of desired character into a plant gives genetically modified crop
(iv) Cross between plants of two species is called as inter varietal hybridisation
(a) (i) and (iii)
(b) (ii) and (iv)
(c) (ii) and (iii)
(d) (iii) and (iv)
Answer:
(a) (i) and (iii)

Question 6.
Weeds affect the crop plants by
(a) killing of plants in field before they grow
(b) dominating the plants to grow
(c) competing for various resources of crops (plants) causing low availability of nutrients
(d) all of the above.
Answer:
(c) competing for various resources of crops (plants) causing low availability of nutrients

Question 7.
Which one of the following species of honey bee is an Italian species?
(a) Apis dorsata
(b) Apis florae
(c) Apis cerana indica
(d) Apis mellifera
Answer:
(d) Apis mellifera

Question 8.
Find out the correct sentence about manure
(i) Manure contains large quantities of organic matter and small quantities of nutrients.
(ii) It increases fire water holding capacity of sandy soil.
(iii) It helps in draining out of excess of water from clayey soil.
(iv) Its excessive use pollutes environment because it is made of animal excretory waste.
(a) (i) and (iii)
(b) (i) and (ii)
(c) (ii) and (iii)
(d) (iii) and (iv)
Answer:
(b) (i) and (ii)

Question 9.
Cattle husbandry is done for the following purposes
(i) Milk Production
(ii) Agricultural work
(iii) Meat production
(iv) Egg production
(a) (i), (ii) and (iii)
(b) (ii), (iii) and (iv)
(c) (iii) and (iv)
(d) (i) and (iv)
Answer:
(a) (i), (ii) and (iii)

Question 10.
Which of the following are Indian cattle?
(i) Bos indicus
(ii) Bos domestica
(iii) Bos bubalis
(iv) Bos vulgaris
(a) (i) and (iii)
(b) (i) and (ii)
(c) (ii) and (iii)
(d) (iii) and (iv)
Answer:
(a) (i) and (iii)

Question 11.
Which of the following are exotic breeds?
(i) Brawn
(ii) Jersey
(iii) Brown Swiss
(iv) Jersey Swiss
(a) (i) and (iii)
(b) (ii) and (iii)
(c) (i) and (iv)
(d) (ii) and (iv)
Answer:
(b) (ii) and (iii)

Question 12.
Poultry farming is undertaken to raise following
(i) Egg production
(ii) Feather production
(iii) Chicken meat
(iv) Milk production
(a) (i) and (iii)
(b) (i) and (ii)
(c) (ii) and (iii)
(d) (iii) and (iv)
Answer:
(a) (i) and (iii)

Question 13.
Poultry fowl are susceptible to the following pathogens
(a) Viruses
(b) Bacteria
(c) Fungi
(d) All of the above
Answer:
(d) All of the above

Very Short Answer Questions

Question 1.
What is FYM?
Answer:
FYM refers to the farmyard manure. It enriches the soil with nitrogen and phosphorus.

Question 2.
What is vermicompost?
Answer:
The compost prepared because of the action of earthworm in decomposition is called vermiform compost.

Question 3.
What is green manuring?
Answer:
Green manuring involves the sowing of seeds of plants like sun hemp and gaur etc before ploughing. After some time they are mulched into soil by ploughing to improve soil fertility.

Question 4.
Name some of the common irrigation systems used in rural areas of India?
Answer:
Irrigation systems used in rural areas of India include dug well, tube well, rivers, canals and water tanks.

Question 5.
What are weeds?
Answer:
Weeds are the unwanted plants which grow at their own in a field.

Question 6.
Name the Indian breeds of (i) Cow and (b) Buffalo
Answer:
(a) Cow-Red sindhi, Sahiwal and Gir.
(b) Buffalo-Murrah, mehsana and Surti.

Question 7.
What are milch animals?
Answer:
Milch animals include the milk producing female population in cattle farming.

Question 8.
How is concentrate different from roughage in cattle diet?
Answer:
Roughage is meant for growing cattle that is poor in proteins and fats but the concentrate is meant for the lactating females which is rich in protein and fats along with vitamins.

Question 9.
Define the followings:
(a) Mixed cropping
(b) Inter cropping
(c) Mixed farming
(d) Crop rotation
Answer:
(a) Mixed cropping : It refers to the simultaneously growing of two or more crops to avoid the crop failure.
(b) Intercropping: It refers to the growing of two or more crops in a definite row pattern to increase the productivity per unit area.
(c) Mixed fanning: It is the cultivation of a crop or more on a field along with rearing and management of cattle for milk or any other animal food product.
(d) Crop rotation: It involves the growing of different crops on a piece of land in a preplanned succession. Mostly legume crop alternates with the cereal crop.

Question 10.
Which practices does the green revolution intend to be adopted to increase the crop production?
Answer:
Green revolution involves growing of large amount of cereal crops using high yielding plant varieties, chemical fertilizers, pesticides, better practices of irrigation, etc.

Question 11.
What are fumigants?
Answer:
These are chemicals sprayed in field or storage sites that in gaseous state are lethal to pests.

Question 12.
What do you man by the acronym HYV?
Answer:
The acronym HYV stands for High yielding variety.

Question 13.
What steps a farmer needs to take to control diseases in cattle?
Answer:
A farmer needs to vaccinate the cattle and isolate the sick cattle from the herd to prevent further infection.

Question 14.
List some of the common diseases of cattle.
Answer:
Cowpox, anthrax, foot and mouth disease and black quarter.

Question 15.
What is the average diet of a cow?
Answer:
A cow on an average needs 15-20 kg of green fodder and dry grass, 4-5 kg of grain mixture and 30-35 litre of water per day.

Question 16.
Name any four breeds of indigenous fowls.
Answer:
Aseel, Chattisgarh, Burosa and Kadakath

Question 17.
Name the two exotic breeds of fowls.
Answer:
Rhode Island Red and White leghorn.

Question 18.
What is the laving period for a layer in poultry farm?
Answer:
Laying period refers to period of time from sexual maturity to the end of the laying of eggs.

Question 19.
Name two technologies adopted in fishing.
Answer:
To have increased output from fishing, echo sounding and satellite imaging is used these days to locate tire fish shoals in oceans.

Question 20.
Name the three commercial products obtained from the bees in beehive.
Answer:
Honey, bee wax and bee venom.

Question 21.
Name some cultured finfishes.
Answer:
Mullets, Pearl spot and Bhekti.

Question 22.
What is the size of bee-hive made of wood?
Answer:
46 × 23 cm., with chambers for laying eggs and collection of honey.

Question 23.
List some of the common pests of bees.
Answer:
Wasp, wax moths, King crow and Green bee eater.

Short Answer Questions

Question 1.
What are micronutrients and macronutrients? Give examples.
Answer:
Micronutrients: The nutrients required in small quantities by plants are called micro nutrients e.g. zinc, copper, boron, etc.

Macronutrients: The nutrients required in large quantities by plants are called macro nutrients e.g. nitrogen, phosphorus, sulphur and potassium.

Question 2.
What are rabi and kharif crops?
Answer:
The crops grown in the winter season are called rabi crops. They are sown in November and harvested in April e.g. wheat, gram, peas, mustard and linseed.

The crops grown in summer season are called kharif crops or crops of monsoon season. They are sown in month of June to be harvested in October e.g. paddy, soyabean, maize and cotton.

Question 3.
How are manures prepared? Give their uses.
Answer:
Manures are prepared by the decomposition of the organic waste that include the plant waste, animal waste like cow dung etc. These wastes are placed ii) a ditch for a period of 1-2 months for decomposition after which they are taken out to be applied in the field.

Manures:

• enrich the soil with organic matter that adds to soil fertility in long rim.
• improves the water holding capacity of the soil.
• help recycle the organic waste produced in a farm.

Question 4.
Differentiate in a manure and fertilizer.
Answer:
A manure is produced naturally by the decomposition of natural plant and animal waste products. It is poor in nutrients but when added to soil, it improves the soil’s water holding capacity.

A fertilizer is industrially manufactured inorganic compound drat is water soluble. When added to soil, it enriches the soil with nutrients but its continuous use leads to soil pollution and in long run leads to a decline in production.

Therefore, fertilizers give only short term benefits but manures give long term benefits.

Question 5.
What precautions should be kept in mind while using fertilizers?
Answer:
The precautions need to be observed when applying fertilizers are

• Apply the fertilizers in terms of proper dose, at proper time after assessing the mineral quantity present in the soil.
• Application of fertilizer must follow proper irrigation, excessive irrigation, may casue their washing away from field.

Question 6.
What is mixed cropping? Give examples.
Answer:
The simultaneous growing of two or more crops on a same piece of land is called mixed cropping. In mixed cropping the common combinations used are:
Maize + Urd bean
Wheat + Chick pea
Ground nut + Sunflower
Cotton + Mung bean
Wheat + Mustard

Question 7.
What do you mean by hybridization? State its types.
Answer:
Hybridization is method of bringing improvement in the varieties of plants for higher yield. It helps produce

• high yielding varieties.
• varieties resistant to pest.
• varieties resistant to drought.

The hybridization is of different types depending upon the selected crop used for the cross pollination by bagging or emasculation. It can be inter-generic, interspecific or inter-species.

Question 8.
Why is there a necessity for the variety improvement?
Answer:
The variety improvement is necessary for

• Higher yield
• Improved quality of agronomic product.
• Biotic and abiotic resistance
• Desirable agronomic characteristics
• Desirable period of maturation time.

Question 9.
What are weeds? How are they controlled?
Answer:
Weeds are the unwanted plants in a cultivated field e.g. a barley or mustard plant in a wheat field. They grow at their own without their cultivation.

These weeds are not good for growing crops because

• they compete with the crop plants for air, water and nutrients.
• they act as alternate host for many pathogens.

Therefore, these weeds need to be removed. Their removal practices involve

• Mechanical method: It involves their manual removal by trowel or hoe.
• Chemical method: It involves the spraying of chemicals called herbicides or weedicides such as 2,4-D and 2,4,5-D.
• Cultural method: It involves proper seed bed preparation, timely sowing of crops, using intercropping or crop rotation practices.

Question 10.
How insect pests harm the crop?
Answer:
Generally, the insect pests harm the crop plants in following ways:

• They cut root, stem or leaf.
• They suck cell sap from different plant parts.
• They bore into stem, root or fruits.

Question 11.
How the diseases of diary animals are classified?
Answer:
The diseases of diary animals are classified as

• Parasitic
• Infectious
• Non-infectious

Parasitic diseases can be caused by the internal parasites like worms or external parasites which cause skin diseases. Infectious diseases are caused by pathogens such as virus, bacteria, fungi, etc.

Question 12.
Name the indigenous and exotic breed of fowls reared in poultry farms.
Answer:
Indigenous breeds of fowl include Aseel, Chattisgarh and Burosa.

Exotic species include Rhode Island Red and White leg horn. Rhode Island Red is a dual type of breed because it has both a good layer and broiler. White leghorn is small size fowl but lay long white egg.

Question 13.
What are broilers? How are they produced?
Answer:
The fowls reared and managed for the purpose of flesh in a poultry farm are called broilers. The broilers chickens are raised for 6-7 weeks in a poultry farm. During this time, they are fed on diet rich in proteins, vitamin-A and vitamin-k and proper care is taken to avoid mortality, feathering and carcass quality. Once they are 750 g to 1.5 kg, they are marketed for flesh.

Question 14.
What are layers? List the factors which have the favourable effect on laying out put.
Answer:
The fowls reared and managed for the purpose of eggs in a poultry farm are called layers. The laying out put refers to the period from the sexual maturity till the end of egg laying period. It is affected by number of factors such as:

• Feeding of the chickens, the feed needs to be rich in vitamins, minerals and micronutrients.
• Feed needs to contain grains of limestone to prevent the laying of shell less eggs.
• The intensity and duration of light is also known to have direct effect on the laying output of eggs.
• Presence of sand bath for chickens to help them get rid of ticks or mites on their skin surface.

Question 15.
What causes diseases to the chicken in a poultry farm? How these diseases can be prevented?
Answer:
In a poultry farm, the different type of pathogens such as virus, bacteria, fungi, etc can cause diseases along with their malnutrition. These diseases can be prevented by

• Proper cleaning and sanitation of the farm.
• Spraying of disinfectants.
• Timely vaccination of chickens.

Question 16.
Give examples of some Indian carps and some marine fishes.
Answer:
Indian carps: Rohu, Catla and Mrigal
Marine fishes: Sardine, Bombay duck, Hilsa, Salmon and Flying fish.

Question 17.
List the quality of the good variety of fishes.
Answer:
The qualities of the good variety of fishes include:

• Good flesh quality.
• Fast growing
• Early maturity.
• Not prone to infections.

Question 18.
State the importance of honey.
Answer:
Honey extracted from beehives

• has value especially indigestion disorders and some liver ailments.
• rich source of calcium and iron along with other minerals and vitamins.
• used as source of sugar in confectioneries.

Question 19.
What are indigenous and exotic breeds of honey bees?
Answer:
Indigenous breeds: Apis cerenana Indica, Apis florae, Apis dorsata
Exotic breeds: Apis mellifera Apis mellifera is the species known for the higher yield of good quality honey.

Question 20.
Which milk will you prefer for making curd, milk of cow or buffalo? Why?
Answer:
The milk from a buffalo is of superior quality because it is richer in fats, tocopherols, proteins, calcium and phosphorus and has low percentage of sodium, potassium and cholesterol. Therefore, for making the dairy products like curd, khoa, ghee and cheese etc, buffalo milk is preferred to cow milk.

Question 21.
What determines the quality of an egg?
Answer:
The quality of an egg is determined by its

• Weight and size.
• Shape
• Shell quality
• Internal structure.

Question 22.
Why ovaprim is used in pisciculture?
Answer:
In pisciculture, to get the good quality of seedlings( very young fishes), hormones extracted from the pituitary gland of carps were used in the process called hypophysation. These days, the hormonal extract has been replaced by synthetic inducing agent containing hormones. This is called ovaprim. It is used to improve the breed of fish synthetically. The use of ovaprim leads to induced breeding of fish.

It is during breeding time of fishes from July to August which is the rainy season.

Question 23.
What is the use of nursery pond and rearing ponds in fish culture?
Answer:
Nursery pond has size of 0.02-0.04 hectare with depth of about one metre. Fish eggs are placed in this pond which has circulating or flowing water to ensure the 100% hatching of the eggs. The eggs after hatching are called fries which are latqr transferred to other pond.

Rearing pond is of size of 0.04 hectare to 0.08 hectare with depth of about 1.5 metre. These are the ponds in which fries are transferred. Here, a they are fed with nutritious food for early maturity.

Question 24.
Enlist some of the advantages of beekeeping.
Answer:
The advantages of beekeeping include

• It is source of honey known for its medical value and source of sugar in confectionaries.
• It is source of bee wax, royal jelly and bee venom,
• It helps in cross pollination of flowers in pasturage,
• It is a type of cheap investment as farmer along with cultivation can involve himself in apiculture to boost his income.

Question 25.
Is water harvesting during monsoon season a better exercise? If yes, why?
Answer:
Yes; water harvesting during rainy season is a good exercise. It involves the storage of water in tanks or in small dams constructed below the higher elevation of catchment area. These dams are local specific but play an important role in

• recharging the underground water level.
• Providing water during times of water scarcity to the local people and cattle.

Question 26.
Mention some of the factors which have helped increase the food production.
Answer:
Some of the factors which have contributed in increasing the food production include

• Use of high yielding varieties of crops.
• Use of manures, fertilizers and adoption of the practices like crop rotation and intercropping.
• Protection of crops from pests and timely eradication of weeds.
• Timely irrigation of field with required amount of water.
• Better storage practices.

Question 27.
Preventive measures needs to be adopted to reduce the incidences of diseases in animals. Explain.
Answer:
The incidences of diseases in animals can be reduced if proper preventive measures are followed such as

• Well desired shelter with proper sanitation and ventilation facilities.
• Proper good nutritious food and good facility for drinking water.
• Keeping the surrounding of the area clean to prevent growth of mosquitoes or othejr pathogens.
• Frequent bathing of animals help reduce skin infections.
• Timely vaccination of animals.

Question 28.
What is crop production? What are the different types of crops?
Answer:
The act of growing number of useful plants in a given area without causing any environmental disturbances is Called crop production. Different types of crops grown are:
Cereals : Wheat, maize, rice, sorghum, millets, etc.
Pulses: Gram pea, black gram, pigeon pea, lentil, kidney beans, etc.
Oil seeds : Mustard, sesame, soyabean, groundnut, sunflower, etc.
Vegetables : Potato, spinach, cabbage, carrot, radish, etc
Fruits: Mango, papaya, grapes, litchi, apple, pine apple, etc.
Fodder: Barseam, oat, etc Beverages: Tea, coffee, tobacco, etc.

Long Answer Type Questions

Question 1.
Write down the differences between mannure and fertilizers.
Answer:
The differences between mannure and fertilisers are given below.
Mannure:

1. This is a mixture of organic and inorganic substances.
2. This is prepared from vegetable and animal wastes by the action of microbes on decomposition.
3. It has low concentration of nutrients.
4. It is not specific in nature.
5. It is bulky hence not easy to store and transport.
6. It adds to water holding capacity of soil.

Fertilizers:

1. This is an inorganic substance.
2. These are synthesised from chemical substances.
3. It has high concentration of nutrients.
4. It is specific in nature e.g. nitrogenous or phosphatic.
5. It is easy to store and transport.
6. It has no effect on water holding capacity of soil.

Question 2.
Explain the role of workers in a honey bee colony.
Answer:
Workers the infertile female in the colony are the most active member. They have almost all responsibilities on their shoulders. In fact, they all are female by instinct but being the infertile female do not have the property to reproduce. Worker in their first half of life cycle do all indoor activities such as cleaning of the hive, taking care of hive as well as the queen.

In the second half of their life cycle they work as field workers i.e. collects the nectar, pollen, propolis. They also act as the security force of the colony i.e. work as the guards of colony. When any enemy comes, they sting it and then die off.

Question 3.
What are the preventive and control measures used before grains are stored for future use.
Answer:
Following are some control measures used before the grains are stored for future use:

1. Drying: The grains should be properly dried in sun followed by drying in shade. So that the moisture contents in the grains should be less than 14%.
2. Maintenance of Hygiene: Godowns and stores should be property cleaned Le., all sorts of dust, dirot, rubbish, webbing etc. of the previous grains should be swept away.
3. Cracks and Holes in the wall, floor or ceiling should be properly sealed.
4. New gunny bags should be used. If the old gunny bags are being used, then clean them properly, turn inside out and expose to the sun or fumigate them.
5. If earthen pots are used then they should also be cleaned and properly exposed to the sun.
6. Fumigation: Chemicals which can exist in gaseous state in sufficient concentration to be lethal against the pest are known as fumigants. These should be used according to the prescribed dose as Aluminium Phosphide can be used at the rate of 2 tablets per tonnes of grain.

Question 4.
What are the objectives of crop-varietal improvement?
Answer:
Common objectives of crop-varietal improvement are as follows:
1. Improved yield: The aim is to improve the productivity of economic produce. This improvement can be brought about by developing high yielding varieties.

2. Better Quality of agronomic products.

3. Biotic and Abiotic resistance: Crops suffer due to bioitic stress under different situtations. Developing varieties which have resistance to these stresses can bring significant improvement in crop production.

4. Early and uniform maturity: Early maturing varieties can make the crop fit into double and multiple cropping systems. This will also reduce the cost of production of crop. Uniform maturity will make the harvesting process easy and reduce the loss of produce harvesting.

5. Desirable Agronomic Traits: Tallness, high tillering and profuse branching are desirable characters for fodder crops. Drawfness is desired in cereals. Thus, developing varietis of desired agronomic traits will help increase the productivity.

6. Water Adaptability: This property will help in stablising the crop production under different environmental conditions.

Question 5.
What is artificial insemination? What are its advantages?
Answer:
Artificial insemination: It is the process of collection of the semen of male animal of desired quality by artificial means. Then its examination, preservation, transportation later it is injected into the vagina of female animals.

This is used only to improve the livestock found at distant places.
Advantages: 1. Artificial insemination makes the selective breeding of animals easier, because the semen from a desired high yielding breed of bull can be transported to distant places for impregnating cows.

2. This process is economical. Semem from a single bull can be used to impregnate 3000 cows at distant places. Thus is because semen of the bull is preserved, packed and sent for artificial insemination.

Question 6.
What practices are employed for rearing of diary animals? Describe essential feature of any two of these practices and their effects on the health and yield of animals.
Answer:
Practices for raising diary animals include:

1. Proper feeding
2. Proper shelter
3. Protection from diseases
4. Breeding

1. Proper feeding: Animals also require balanced diet in adequate quantity according to their work, special conditions, age and health. Animal requirements is of two types (1) Roughages (2) Concentrate. Green fodder, berseem, maize, jowar, bajra, provide them with some minerals. Cereals, grains, cotton, seeds, oil cakes and gram provide them with concentrate consisting proteins, fats and vitamins at the time of lactation.

Effect of Proper feeding. The poor quality of food material is the main .reason for the overall low yield. Their deficiency may cause diseases and affect the general health of the animals. Proper feeding maintain general health as well as raises the yield of the animal product.

2. Breeding: It is also very important factor for rearing dairy animals. Our indigenous varieties yield low milk, eggs and meat evert on their proper feeding Traditional breeds of animals are improved by crossing them, with high yielding breeds.

Question 7.
What is the important points to remember in poultry farming?
Answer:
The important points to remember in poultry farming are following:

1. Thr iMpNiwiii poultry breeds should be developed and fanned to produce layers for eggs and broilers for meat.
2. We should improve their breed by cross breeding the indigenous with exotic breeds according to their use (layers or broilers).
3. Their housing, shelters and feed should be kept in mind as layers require enough space as compared to broilers, layers also need proper light. Food is also different for broilers towhom we have to supply more protein rich diet with adequate fat. The layers are fed with vitamins, minerals and micronutrients.
4. The keeper should practice proper sanitation, spraying of disinfectant at regular intervals to avoid the spread of diseases.
5. Appropriate vaccination to reduce loss of poultry during an out break of disease, so, keeper should also keep in mind the vaccination process.

Question 8.
How bee colony works? What values can be seen in organisation of colony?
Answer:
Bees, live in a colony and show the best example of teamwork. The colony has three types of bees (1) Queen (2) Drones (3) Workers.

1. Queen: Is only one in one colony. Works as a mother of the colony, is responsible for laying eggs. In each season 2000 eggs are laid per day, eggs are fertile as well as.unfertile. Queen and workers emerges from fertile teggs where as drones come out of unfertile eggs.

2. Drones: They work as male in colony and mate with the queen. They live., sleep and eat in the colony. Their role is only in the breeding season hence, they are made to leave the colony after the breeding seasons. They are hundreds in number in one hive.

3. Workers: These are the most active members of the colony. They are female by instinct but unable to reproduce. During their first half life period, they perform the indoor duty as cleaning of hive etc. In the second half of their life, they have to do the outdoor duties such as collection of nectar, pollen, bee glue and protection of the queen. They are the security guards hence, sting the enemies and die off. They are 40,000 to 100,000 in a hive.

Question 9.
Explain what will happen if in a cultivated field only mannures are supplied and in another field only fertiliser are supplied while keeping all other conditions similar.
Answer:
In a cultivated field if we supply the manures, it will enrich the soil with nutrients as well as with organic matter. Manures increase the water holding capacity of the soil but in clayey soil the organic matter of manure helps in drainage and avoid water logging. Manure protect our environment and by applying it, we recycle the farm waste which is of so costly. But manure supply the small quantities of nutrients. The result would be slow plant growth.

In the another field we supply only fertilisers, the plants then have the healthy vegetative growth giving rise to healthy plants. Fertilisers are commercially produced for giving nutrients to plants and can supply only Nitrogen, Phosphorus or potassium (NPK). We can obtain high yield but only in high cost farming practices. We have also to keep in mind the pre and post application precautions for their utilization. Fertiliser is to be applied in terms of proper dose and time.

This results that when the farmer apply only fertiliser, he will get better cultivation and high yield as compared to when we only the manures. However, fertilizers if applied in excess would promote desertification.

These NCERT Solutions for Class 9 Science Chapter 14 Natural Resources Questions and Answers are prepared by our highly skilled subject experts to help students while preparing for their exams.

Natural Resources NCERT Solutions for Class 9 Science Chapter 14

Class 9 Science Chapter 14 Natural Resources InText Questions and Answers

Question 1.
How is our atmosphere different from the atmospheres on Venus and Mars?
Answer:
Earth’s atmosphere is different from those of Venus and Mars. This difference lies essentially in their compositions. Earth’s atmosphere is a mixture of nitrogen (79%), oxygen (20%), and a small fraction of carbon dioxide, water vapours and other gases. This makes the existence of life possible on Earth. However, the atmospheres on Venus and Mars mainly consist of carbon dioxide. The amount of carbon dioxide on these planets can range from 95% to 97%.

Question 2.
How does the atmosphere act as a blanket?
Answer:
The atmosphere acts as a blanket by performing the following functions:
(a) It keeps the average temperature of the Earth fairly constant during daytime and even during the course of whole year.
(b) It prevents a sudden increase in the temperature during daytime.
(c) It slows down the escape of heat from the surface of the Earth into outer space during nighttime.

Question 3.
What causes winds?
Answer:
An uneven heating of the Earth’s surface causes winds. On being heated, air becomes lighter and rises up. As a result, a region of low pressure is created. Then, air from a high pressure region moves to a low pressure region, causing wind.

Question 4.
How are clouds formed?
Answer:
During daytime, on being heated, a large amount of water evaporates from various water bodies and goes into the air. A part of this water vapour also reaches the atmosphere through biological activities such as transpiration and respiration. This causes the air in the atmosphere to heat up. When this heated air rises, it expands and cools, which results in the condensation of water vapour forming water droplets. The presence of dust and other suspended particles in air also facilitates the process of condensation. The formation of water droplets leads to the formation of clouds.

Question 5.
List any three human activities that you think would lead to air pollution.
Answer:
The following three human activities would lead to air pollution:

1. Burning of fossil fuels such as coal and petroleum
2. Industrialization
3. Deforestation

Question 6.
Why do organisms need water?
Answer:
Organisms need water for the following reasons:

• All cellular processes need water as a medium. Usually, the reactions that take place in our body or within the cells occur between substances that are dissolved in water.
• Since most of the substances are transported in a dissolved form, water is necessary.

Question 7.
What is the major source of fresh water in the city/town/village where you live?
Answer:
River is a major source of freshwater.

Question 8.
Do you know of any activity which may be polluting this water source?
Answer:
The discharge of wastewater from homes, industries, hospitals, etc. into the river pollutes this freshwater source.

Question 9.
How is soil formed?
Answer:
Soil is formed by breaking down of rocks at or near the surface of the Earth through various physical, chemical, and biological processes by various factor such as the sun, water, wind, and living organisms.
(i) Sim:
During day time, the rocks are heated. This
causes the rocks to expand. During nighttime, these rocks cool down and contract. Since all parts of the rock do not undergo expansion and contraction at the same rate, this causes the formation of cracks in these rocks. These cracks lead to the breaking up of huge rocks into smaller pieces.

(ii) Water:
Water catalyses the process of formation of soil in two ways.
(a) Water goes into the cracks and crevices formed in the rocks. When this water freezes, its volume increases. As a result, the size of the cracks also increases. This helps in the weathering of rocks.
(b) Running water wears away hard rocks over long periods of time. Water moving in fast speed carries big and small particles of rock downstream. These rocks rub against each other, resulting in breaking down of rocks. These smaller particles are carried away by running water and deposited down its path.

(iii) Wind:
Strong winds carry away rocks, which causes rubbing of rocks. This results in the breaking down of rocks into smaller and smaller particles.

(iv) Living organisms:
Some living organisms like lichens help in the formation of soil. Lichens also grow on rocks. During their growth, lichens release certain substances, which cause the rock surface to powder down forming a thin layer of soil. On this thin layer of soil, some small plants like moss also grow. They further cause the breaking down of the rock particles.

Question 10.
What is soil erosion?
Answer:
The blowing away or washing away of land surface by wind or water is known as soil erosion.

Question 11.
What are the methods of preventing or reducing soil erosion?
Answer:
The methods of preventing or reducing soil erosion are:

• Prevention of deforestation
• Plantation of trees

Question 12.
What are the different states in which water is found during the water cycle?
Answer:
During the water cycle, water is found in solid state (snow, ice, etc.), liquid state (ground water, river water, etc.), and gaseous state (water vapours).

Question 13.
Name two biologically important compounds that contain both oxygen and nitrogen.
Answer:
Two biologically important compounds that contain both oxygen and nitrogen are:

1. Amino acids
2. Deoxyribonucleic acid (DNA) and Ribonucleic acid (RNA)

Question 14.
List any three human activities which would lead to an increase in the carbon dioxide content of air.
Answer:

1. Burning of fuels in various processes like heating, cooking, transportation, and industry.
2. Human induced forest fires
3. The process of deforestation includes the cutting down of trees. This decreases the uptake of carbon dioxide for photosynthesis. Eventually, the content of carbon dioxide increases.

Question 15.
What is the greenhouse effect?
Answer:
Some gases like carbon dioxide, methane, nitrous oxide prevent the escape of heat from the Earth’s surface by trapping it. This increases the average temperature of the Earth. This is called the greenhouse effect. An increase in the content of such gases would lead to a situation of global warming.

Question 16.
What are the two forms of oxygen found in the atmosphere?
Answer:
The two forms of oxygen found in the atmosphere are:

1. Diatomic molecular form with chemical formula O2.
2. Triatomic molecular form with chemical formula O3 known as ozone.

Class 9 Science Chapter 14 Natural Resources Textbook Questions and Answers

Question 1.
Why is the atmosphere essential for life?
Answer:
The atmosphere is essential for life because it maintains an appropriate climate for the sustenance of life by carrying out the following activities:

• Atmosphere keeps the average temperature of the Earth fairly constant during daytime.
• It prevents a sudden increase in temperature during daytime.
• It also slows down the escape of heat from the surface of the Earth into outer space during nighttime.

Question 2.
Why is water essential for life?
Answer:
Water is essential for life because of the following reasons:

• Most biological reactions occur when substances are dissolved in water. Thus, all cellular processes need water as a medium to take place.
• Transportation of biological substances needs water as a medium.

Question 3.
How are living organisms dependent on the soil? Are organisms that live in water totally independent of soil as a resource?
Answer:
Almost all living organisms are dependent on soil. Some depend directly, while some depend indirectly.

Plants need soil for getting support as well as nutrients to prepare their food. On the other hand, organisms depend on plants for food and other substances that are essential for life. Herbivores depend directly upon plants, and carnivores depend upon animals, which in turn depend upon plants for food. This makes them depend on soil indirectly.

Organisms that live in water are not totally independent of soil as a resource. These organisms depend on aquatic plants for food and other substances. These aquatic plants in turn require minerals for their sustenance. These minerals are carried to water bodies from soil by rivers, rainwater, etc. Without the supply of minerals from the soil to the water bodies, it is impossible to imagine aquatic life.

Question 4.
You have seen weather reports on television and in newspapers. How do you think we are able to predict the weather?
Answer:
The meteorological department of the government collects data on the elements of weather such as maximum and minimum temperatures, maximum and minimum humidity, rainfall, wind speed, etc. They are able to study these elements using various instruments. The maximum and minimum temperature of a day is measured by a thermometer known as the maximum-minimum thermometer. Rainfall is measured by an instrument known as the rain gauge. Wind speed is measured by anemometers. There are various instruments used to measure humidity.

Question 5.
We know that many human activities lead to increasing levels of pollution of the air, water-bodies and soiL Do you think that isolating these activities to specific and limited areas would help in reducing pollution?
Answer:
Yes. Isolating human activities to specific areas would help in reducing levels of pollution. For example, setting up of industries in isolated regions will control pollution to some extent. The pollution caused by these industries will not contaminate water resources, agriculture land, fertile land, etc.

Question 6.
Write a note on how forests influence the quality of our air, soil and water resources.
Answer:
Forests influence the quality of our air, soil, and water resources in various ways. Some of them are:

• Forests balance the percentages of carbon dioxide and oxygen in the atmosphere. The increasing amount of carbon dioxide caused by human activities is balanced by a larger intake of carbon dioxide by plants during the process of photosynthesis. Simultaneously, a large amount of oxygen is released.
• Forests prevent soil erosion. Roots of plants bind the soil tightly in a way that the surface of the soil cannot be eroded away by wind, water, etc.
• Forests help in the replenishment of water resources. During the process of transpiration, a huge amount of water vapour goes into the air and condenses to form clouds. (These clouds cause rainfall that recharge water bodies.

Class 9 Science Chapter 14 Natural Resources Additional Important Questions and Answers

Choose the correct option:

Question 1.
The atmosphere of the earth is heated by radiations which are mainly
(a) radiated by the sun
(b) re-radiated by land
(c) re-radiated by water
(d) re-radiated by land and water
Answer:
(d) re-radiated by land and water

Question 2.
If there were no atmosphere around the earth, the temperature of the earth will
(a) increase
(b) go on decreasing
(c) increase during day and decrease during night
(d) be unaffected
Answer:
(c) increase during day and decrease during night

Question 3.
What would happen, if all the oxygen present in the environment is converted to ozone?
(a) We will be protected more
(b) It will become poisonous and kill living forms
(c) Ozone is not stable, hence it will be toxic
(d) It will help harmful sun radiations to reach earth and damage many life forms.
Answer:
(b) It will become poisonous and kill living forms

Question 4.
One of the following factors does not lead to soil formation in nature
(a) the sun
(b) water
(c) wind
(d) polythene bags
Answer:
(d) polythene bags

Question 5.
The two forms of oxygen found in the atmosphere are
(a) water and ozone
(b) water and oxygen
(c) ozone and oxygen
(d) water and carbon-dioxide
Answer:
(c) ozone and oxygen

Question 6.
The process of nitrogen-fixation by bac¬teria does not take place in the presence of
(a) molecular form of hydrogen
(b) elemental form of oxygen
(c) water
(d) elemental form of nitrogen
Answer:
(b) elemental form of oxygen

Question 7.
Rainfall patterns depend on
(a) the underground water table
(b) the number of water bodies man area
(c) the density pattern of human population in an area
(d) the prevailing season in an area
Answer:
(b) the number of water bodies man area

Question 8.
Among the given options, which one is not correct for the use of large amount of fertilisers and pesticides?
(a) They are eco-friendly
(b) They turn the fields barren after some time
(c) They adversely affect the useful component from the soil
(d) They destroy the soil fertility
Answer:
(a) They are eco-friendly

Question 9.
The nitrogen molecules present in air can be converted into nitrates and nitrites by
(a) a biological process of nitrogen fixing bacteria present in Soil
(b) a biological process of carbon fixing factor present in soil
(c) any of the industries manufacturing nitrogenous compounds
(d) the plants used as cereal crops in field
Answer:
(a) a biological process of nitrogen fixing bacteria present in Soil

Question 10.
One of the following processes is not a step involved in the water-cycle operating in nature
(a) evaporation
(b) transpiration
(c) precipitation
(d) photosynthesis
Answer:
(d) photosynthesis

Question 11.
The term “water-pollution” can be defined in several ways. Which of the following statements does not give the correct definition?
(a) The addition of undesirable substances to water-bodies
(b) The removal of desirable substances from water-bodies
(c) A change in pressure of the water bodies
(d) A change in temperature of the water bodies
Answer:
(c) A change in pressure of the water bodies

Question 12.
Which of the following is not a greenhouse gas?
(a) Methane
(b) Carbon dioxide
(c) Carbon monoxide
(d) Ammonia
Answer:
(d) Ammonia

Question 13.
Which step is not involved in the carbon-cyicle?
(a) Photosynthesis
(b) Transpiration
(c) Respiration
(d) Burning of fossil fuels
Answer:
(b) Transpiration

Question 14.
‘Ozone-hole’ means
(a) a large sized hole in the ozone layer
(b) thinning of the ozone layer
(c) small holes scattered in the ozone layer
(d) thickening of ozone in the ozone layer
Answer:
(b) thinning of the ozone layer

Question 15.
Ozone-layer is getting depleted because of
(a) excessive use of automobiles
(b) excessive formation of industrial units
(c) excessive use of man-made compounds containing both fluorine and chlorine
(d) excessive deforestation.
Answer:
(c) excessive use of man-made compounds containing both fluorine and chlorine

Question 16.
Which of the following is a recently originated problem of environment?
(a) Ozone layer depletion
(b) Greenhouse effect
(c) Global warming
(d) All of the above

Very Short Answer Questions

Question 1.
Define the term natural resource.
Answer:
Any useful material obtained from the nature is called a natural resource.

Question 2.
What are two types of natural resources?
Answer:
The two types of natural resources are renewable resources and non-renewable resources.

Question 3.
Which zone of atmosphere is the closet to the earth?
Answer:
Troposphere

Question 4.
Name the three important constituents of the air.
Answer:
The three important constituents of soil are nitrogen, oxygen and carbon dioxide.

Question 5.
Where on earth the British researchers have found the ozone hole in 1985?
Answer:
Over South Antarctica.

Question 6.
Montreal protocol in 1986 had banned on the emission of a pollutant to protect the ozone layer. Name the pollutant.
Answer:
Montreal protocol had banned the emission of CFCs (Chlorofluro carbon)

Question 7.
Name some of the greenhouse gases.
Answer:
Carbon dioxide, methane, sulphur dioxide and CFCs.

Question 8.
Which two types of components are found in biosphere?
Answer:
Biotic (living) components and abiotic (Non-living) components.

Question 9.
List the factors which contribute to the weathering of rocks in soil formation.
Answer:
The factors are temperature, air, water and living organisms like lichens.

Question 10.
Which factor is responsible for deciding the type of soil?
Answer:
The average particle size decides the type of soil.

Question 11.
Which type of soil causes early waterlogging conditions?
Answer:
Clayey soil

Question 12.
Why is there a need to conserve the natural resources?
Answer:
The conservation of natural resources is essential for the sustainable development.

Question 13.
What is biosphere?
Answer:
The life supporting zone, of the earth where the lithosphere, hydrosphere and atmosphere interact is called biosphere.

Question 14.
What do you understand by top soil?
Answer:
The top soil is the uppermost layer of soil that contains humus and living organisms in addition to soil particles. It also holds the plants.

Question 15.
Name the three forms of nitrogen fixation.
Answer:
The three forms of nitrogen fixation are atmospheric fixation, biological fixation and industrial fixation.

Short Answer Questions

Question 1.
What is atmosphere? State its importance to life on the earth.
Answer:
A thick blanket of air present around the earth is called atmosphere. It is a bad conductor of heat as during day time, the atmospheric gases prevents excessive rise in surface temperature of the earth for the survival of life and at night time the same gases prevent the escape of heat from earth surface to keep it warm.

The air present in atmosphere also contains life supporting gases such as oxygen and carbon dioxide.

Question 2.
Mention the different constituents of the soil.
Answer:
The different constituents of soil are

• Powdered rock particles formed after the weathering of rocks.
• Micro-organisms included in the decomposition of organic matter.
• Water droplets
• Organisms like earthworm for whom the top soil acts as their habitat.

Question 3.
Why is soil important for plants?
Answer:
Soil is important to plants because it is a source of

• water required by the plants.
• mineral nutrients required by the plants
• support required by plants to stand erect even in windy or stormy conditions.

Question 4.
What is soil pollution?
Answer:
The removal of useful components of soil and the addition of other substances which interfere with the soil fertility and harm the diversity of microorganisms present in soil is called soil pollution. The application of chemical fertilizers, pesticides and addition of domestic and industrial waste to soil, along with increased degree of soil erosion are the major causes of soil pollution.

Question 5.
Differentiate in water table and water depth.
Answer:
The minimum depth fo soil where all pore spaces in soil are filled with water make up the water table. Thus, the upper level zone of saturation is called water table.The depth of water level is expressed with reference to mean sea level.

The vertical distance from place on the surface of the earth to the water table is called the water level.

Question 6.
Differentiate in the two types of components found in the biosphere.
Answer:
The types of the components found in the biosphere are biotic and abiotic components. The biotic components include all living organisms from microorganisms to higher plants and animals. The abiotic components include all non-living components such as air, water and soil.

Question 7.
Why do we need to conserve the natural resources?
Answer:
The conservation of natural resources means their wise and judicious use. It is essential to conserve the different natural resources to ensure

• The availability of natural resources for a longer time.
• The maintenance of the quality of the natural resources.
• To achieve the sustainable development.

Question 8.
List two ways in which carbon dioxide is fixed in nature.
Answer:
The carbon dioxide is fixed in nature by

1. Green plants who produce sugar by the reduction of carbon dioxide in photosynthesis.
2. Aquatic mostly marine animals molluscs who use carbonates present in seawater to make their protective shell

Question 9.
Mention some of the pollutants of air.
Answer:
Any undesirable substance added to air that causes the decline in the quality of air is called air pollutant. The different air pollutants include:

• Oxides of sulphur such as SO₂ and SO₃.
• Oxides of nitrogen such as NO and NO₂
• Greenhouse gases such as methane and carbon dioxide
• Unburnt particles of carbon called soot.
• Carbon monoxide
• Dust and smoke

Question 10.
What is smog?
Answer:
The presence of oxides of sulphur, oxides of nitrogen, greenhouse gases such as methane and carbon dioxide, unburnt particles of carbon, dust and smoke in air mixes with fog to form smog in cold weather conditions. The smog formation reduces the visibility that harms the productivity because of the delay in travelling times, corrosion of metallic and marble structures.

Question 11.
Describe ozone as a chemical weed.
Answer:
Ozone is considered as a chemical weed because when on earth surface as a bluish gas, it is toxic to life but high up in stratosphere, it protects the life from the UV-rays present in solar radiations. The UV rays have harmful effects on human life because they are considered responsible for

• Increasing incidences of skin bums and skin cancer.
• Increasing cases of cataract.
• Reducing crop production by more than 20%.

Question 12.
Which chemicals have reduced the thickness of ozone layer in stratosphere?
Answer:
Man made compounds called CFCs (Chlorofluro carbons) are very stable compounds. These compounds released from refrigerators and air conditioners cannot be degraded by any biological process. When they reach the ozone layer, the chlorine present in them combines with the monatomic oxygen produced on the dissociation of ozone to form stable compound. This continuously occurring reaction causes fire depletion of ozone layer.

Nitric oxide (NO) released in air also contributes to the depletion of the ozone layer.

Long Answer Questions

Question 1.
How the two biological processes respiration and photosynthesis are interrelated? Give an example to support your answer.
Answer:
The two biological processes, photosynthesis and respiration are interrelated because the end products of cellular respiration i.e. carbon dioxide and water are the raw materials in the process of photosynthesis and the end products of photosynthesis i.e. sugar and oxygen are the raw materials used in the process of cellular respiration.
Respiration,
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy
Photosynthesis,
6CO₂ + 12H₂O + Solar energy → C₆H₁₂O₆ + 6H₂O + 6O₂

Therefore, in green plants during early morning and later evening, no gaseous exchange takes place as at this time, rate of photosynthesis equals the rate of respiration taking place in their cells.

Question 2.
Explain the water cycle with the help of a diagram.
Answer:
The water cycle involves

• the evaporation of water in form of its vapours from the earth surface and hydrosphere under the heating effect of solar radiations.
• the condensation of water vapours high up in atmosphere to form clouds containing water in its condensed form of water droplets.
• the precipitation that returns the water back to earth in form of rain, hail or snow.

Question 3.
Draw and explain nitrogen cycle in nature.
Answer:
Nitrogen is almost chemically inert gas but is the major constituent of the atmospheric air. (78%) It cannot be directly used by the plants and animals but is essential for all living organisms being the major constituent of proteins and nucleic acids. Therefore, the atmospheric nitrogen is first fixed in form of compounds that can easily be absorbed by the plants.

In nature nitrogen fixation occurs in three possible ways. These are

• Atmospheric fixation, when lightning occurs during thunder storm. The nitrogen combines with oxygen to form its oxide or nitrogen combines with hydrogen to form ammonia. These oxides being water soluble reach the earth with rainwater.
• Biological fixation which is carried out by the free nitrogen fixing cyanobacteria like nostoc and anabena or by the bacteria named Rhizobium present in the root nod-ules of legume plants.
• Industrial fixation involves the formation of nitrogen compounds by chemical fertilizer producing companies.

The nitrogen compounds present in soil in form of nitrites undergo nitrification by bacterial action to form nitrate ions that are absorbed by the plants and used up in synthesis of proteins and nucleic acids. From plants, the nitrogen compounds reach animals in form of amino acids and nitrogenous bases for their growth.

The plant and animal waste or their dead parts later undergo either decomposition to produce nitrite or nitrates or undergo bacterial denitrification to release the nitrogen in gaseous state in nature.

Question 4.
How is carbon cycle completed in nature?
Answer:
Carbon is incorporated into plants by process of photosynthesis. The process converts the gaseous carbon dioxide present in atmosphere or dissolved in water into glucose molecules. These molecules are the source of energy after their oxidation in the process of respiration. The process involves the release of carbon dioxide back in the atmosphere.

The compounds of carbon in different forms of carbohydrates, proteins and fats passes into animals for their survival.

The process of combustion of fuels also adds carbon dioxide to the atmosphere. The combustion involves the oxidation of compounds of carbon or carbon alone to produce energy in the form of heat and light. A small percentage of carbon in gaseous state is also released on the decomposition of organic matter by decomposers. A small percentage of carbon dioxide dissolved in water is also involved in formation of carbonates that are used by aquatic animals to make shells.

Hence, carbon in form of carbon dioxide cycles in nature between living organisms and atmospheric air.

Question 5.
Explain the oxygen cycle in nature.
Answer:
Oxygen gas is very important for most of the living organisms and is also abundantly available in atmospheric air, 21% by volume of the total atmospheric air. It is also present in form of its compounds in lithosphere such as metallic oxides and form of oxides of carbon, sulphur and nitrogen in air. In living organisms, it is the major constituents of essential organic compounds like carbohydrates, fats, etc.

In atmosphere, the oxygen is used in three processes i.e. respiration, combustion and formation of oxides. The used oxygen is returned to atmosphere by the process of photosynthesis in which it is released as the end product.

These NCERT Solutions for Class 9 Science Chapter 13 Why Do We Fall Ill Questions and Answers are prepared by our highly skilled subject experts to help students while preparing for their exams.

Why Do We Fall Ill NCERT Solutions for Class 9 Science Chapter 13

Class 9 Science Chapter 13 Why Do We Fall Ill InText Questions and Answers

Question 1.
State any two conditions essential for good health.
Answer:
The two conditions essential for good health are:

1. An individual must have better health facilities and more professionals to deal with health problems.
2. All basic necessary conditions to prevent diseases must be present. For example, proper garbage collection and disposal, clearing of drains, supply of healthy drinking water, etc.

Question 2.
State any two conditions essential for being free of disease.
Answer:
The two conditions essential for being free of diseases are:

1. Personal hygiene and cleanliness are necessary to stay away from diseases.
2. Individuals should take a balanced diet that contains carbohydrates, fats, proteins, vitamins, fibres, and proper quantity of water.

Question 3.
Are the answers to the above questions necessarily the same or different? Why?
Answer:
No. The answers to the above questions may not necessarily be the same. This is because a disease free state is not the same as being healthy. Good health is the ability of an individual to realise his or her full potential. Individuals can have poor health without having any identifiable disease. Also, health is related to society and community, whereas having a disease is about an individual sick person. Hence, the conditions for good health and for being disease free can be same or even different.

Question 4.
List any three reasons why you would think that you are sick and ought to see a doctor. If only one of these symptoms were present, would you still go to the doctor? Why or why not?
Answer:
Symptoms such as a headache, stomach pain, nausea, vomiting, fever, etc., make us feel that we are sick and must visit a doctor. These symptoms basically indicate that there might be a disease, but we cannot predict the kind of disease. Therefore, it becomes necessary to visit a doctor so that the disease can be identified and can be treated with proper medication.

However, if only one of these symptoms is present, we usually do not visit a doctor. This is because such symptoms do not have much effect on our general health and ability to work. However, if a person is experiencing these symptoms for quite sometime, then he needs to visit a doctor for proper treatment.

Question 5.
In which of the following case do you think the long-term effects on your health are likely to be most unpleasant?

• If you get jaundice,
• If you get lice,
• If you get acne.

Why?
Answer:
Jaundice is a disease that can cause long-term effects on our health. It is a chronic disease that lasts for a long period of time. Jaundice does not spread rapidly, but it develops slowly over a period of time.

Question 6.
Why are we normally advised to take bland and nourishing food when we are sick?
Answer:
We are normally advised to consume bland and nourishing food when we are sick so that we can get the nutrients and energy quickly to fight off the foreign disease-causing agents.

Question 7.
What are the different means by which infectious diseases are spread?
Answer:
Diseases can be spread through various means such as air, water, sexual contact, blood, and vector.

• Certain disease-causing micro-organisms are expelled in air by coughing, sneezing, talking, etc. These micro-organisms can travel through dust particles or water droplets in air to reach other people. For example, tuberculosis, pneumonia, etc. spread through air.
• Sometimes causal micro-organisms get mixed with drinking water and spread water borne diseases. Cholera for example is waterborne disease.
• Sexual act between two people can lead to the transfer of diseases such as syphilis, gonorrhoea, AIDS, etc.
• Certain diseases such as AIDS can spread via blood-to-blood contact during blood transfusion or pregnancy.
• Certain diseases spread by animals called vectors. For example mosquitoes spread malaria.

Question 8.
What precautions can you take in your school to reduce the incidence of infectious diseases?
Answer:
Precautions to reduce incidence of infectious diseases are:

• Stay away from the diseased person.
• Cover your mouth or nose while coughing or sneezing to prevent the spread of disease.
• Drink safe water.
• Keep the environment clean to prevent mosquitoes from breeding.

Question 9.
What is immunization?
Answer:
Immunizations defined as protection of the body from communicable diseases by administration of some agent that mimics the microbe. This suspension of killed microbes that mimics the disease-causing microbes is known as vaccines.

Question 10.
What are the immunization programmes available at the nearest health centre in your locality? Which of these diseases are the major health problems in your area?
Answer:
The immunization programmes available at the nearest health centre are DPT (Diphtheria, Pertusis, and Tetanus), polio vaccine, hepatitis B, MMR (Measles, Mumps, and Rubella), jaundice, typhoid, etc.

Of all these diseases, jaundice and typhoid are major health problems.

Class 9 Science Chapter 13 Why Do We Fall Ill Textbook Questions and Answers

Question 1.
How many times did you fall ill in the last one year? What were the illnesses?
(a) Think of one change you could-make in your habits in order to avoid any of /most of the above illnesses.
(b) Think of one change you would wish for in your surroundings in order to avoid any of/most of the above illnesses.
Answer:
This varies from person to person. Some people fall ill several times in a year, while others do not fall ill at all. A person’s immune system and hygiene-related habits play a major role in determining the person’s health.

Question 2.
A doctor/nurse/health worker is exposed to more sick people than others in the community. Find out how she/he avoids getting sick herself/himself.
Answer:
The following precautions must be taken by a doctor/ nurse/ health-worker:

• Wearing a mask when in contact with a diseased person.
• Keeping yourself covered while moving around an infected place.
• Drinking safe water.
• Eating healthy and nutritious food.
• Ensuring proper cleanliness and personal hygiene.

Question 3.
Conduct a survey in your neighbourhood to find out what the three most common diseases are. Suggest three steps that could be taken by your local authorities to bring down the incidence of these diseases.
Answer:
Three most common diseases are:

1. Tuberculosis
2. Typhoid
3. Jaundice

Steps to be taken to bring down the incidence of these diseases are:

1. Proper disposal of sewage.,
2. Ensuring supply of safe drinking water.
3. Providing a clean environment and preventing mosquitoes from breeding.

Question 4.
A baby is not able to tell her/his caretakers that she/he is sick. What would help us to find out
(a) that the baby is sick?
(b) what is the sickness?
Answer:
(a) The baby is sick can be determined by his/ her behavioural changes such as constant crying of baby, improper intake of food, frequent mood changes, etc.
(b) The sickness is determined by symptoms or indications that can be seen in the baby. The symptoms include vomiting, fever, loose motion, paleness in the toe body, etc.

Question 5.
Under which of the following conditions is a person most likely to fall sick?
(a) when she is recovering from malaria.
(b) when she has recovered from malaria and is taking care of someone suffering from chickenpox.
(c) when she is on a four-day fast after recovering from malaria and is taking care of someone suffering from chickenpox.
Why?
Answer:
(c) A person is more likely to fall sick when she is cm a four day fast after recovering from malaria and is taking care of someone who is suffering from chickenpox. This is because she is fasting during recovery, and her immune system is so weak that it is not able to protect its own body from any foreign infection. If she is taking care of someone suffering from chickenpox, then she has more chances of getting infected from chickenpox virus and will get sick again with this disease.

Question 6.
Under which of the following conditions are you most likely to fall sick?
(a) when you are taking examinations.
(b) when you have travelled by bus and train for today.
(c) when your friend is suffering from measles.
Why?
Answer:
(c) You are more likely to fall sick when your friend is suffering from measles. This is because measles is highly contagious and can easily spread through respiration i.e., through air. Thus, if your friend is suffering from measles, stay away from him otherwise you might easily get infected with the disease.

Class 9 Science Chapter 13 Why Do We Fall Ill Additional Important Questions and Answers

Choose the correct option:

Question 1.
Which one of the following is not a viral disease?
(a) Dengue
(b) AIDS
(c) Typhoid
(d) Influenza
Answer:
(c) Typhoid

Question 2.
Which one of the following is not a bacterial disease?
(a) Cholera
(b) Tuberculosis
(c) Anthrax
(d) Influenza
Answer:
(d) Influenza

Question 3.
Which one of the following diseases is not transmitted by mosquitoes?
(a) Brain fever
(b) Malaria
(c) Typhoid
(d) Dengue
Answer:
(c) Typhoid

Question 4.
Which one of the following disease is caused by bacteria?
(a) Typhoid
(b) Anthrax
(c) Tuberculosis
(d) Malaria
Answer:
(d) Malaria

Question 5.
Which one of the following diseases is caused by protozoans?
(a) Malaria
(b) Influenza
(c) AIDS
(d) Cholera
Answer:
(a) Malaria

Question 6.
Which one of the following has a long-term effect on the health of an individual?
(a) Common cold
(b) Chickenpox
(c) Chewing tobacco
(d) Stress
Answer:
(c) Chewing tobacco

Question 7.
Which of the following can make you ill if you come in contact with an infected person?
(a) High blood pressure
(b) Genetic abnormalities
(c) Sneezing
(d) Blood cancer
Answer:
(c) Sneezing

Question 8.
AIDS cannot be transmitted by
(a) sexual contact
(b) hugs
(c) breastfeeding
(d) blood transfusion
Answer:
(b) hugs

Question 9.
Making anti-viral drugs is more difficult than making anti-bacterial medicines because
(a) viruses make use of host machinery
(b) viruses are on the borderline of living and non-living
(c) viruses have very few biochemical mechanisms of their own
(d) viruses have a protein coat
Answer:
(c) viruses have very few biochemical mechanisms of their own

Question 10.
Which one of the following causes kala-azar?
(a) Ascaris
(b) Trypanosoma
(c) Leishmania
(d) Bacteria
Answer:
(c) Leishmania

Question 11.
If you live in a overcrowded and poorly ventilated house, it is possible that you may suffer from which of the following diseases
(a) Cancer
(b) AIDS
(c) Airborne diseases
(d) Cholera
Answer:
(c) Airborne diseases

Question 12.
Which disease is not transmitted by mosquitoes?
(a) Dengue
(b) Malaria
(c) Brain fever or encephalitis
(d) Pneumonia
Answer:
(d) Pneumonia

Question 13.
Which one of the following is not important for individual health?
(a) Living in clean space
(b) Good economic condition
(c) Social equality and harmony
(d) Living in a large and well furnished house
Answer:
(d) Living in a large and well furnished house

Question 14.
Choose the wrong statement
(a) High blood pressure is caused by excessive weight and lack of exercise.
(b) Cancers can be caused by genetic abnormalities
(c) Peptic ulcers are caused by eating acidic food
(d) Acne in not caused by staphylococci
Answer:
(c) Peptic ulcers are caused by eating acidic food

Question 15.
We should not allow mosquitoes to breed in our surroundings because they
(a) multiply very fast and cause pollution
(b) are vectors for many diseases
(c) bite and cause skin diseases
(d) are not important insects
Answer:
(b) are vectors for many diseases

Very Short Answer Questions

Question 1.
Write the full form of AIDS.
Answer:
AIDS stand for Acquired immunodeficiency syndrome.

Question 2.
Name the three diseases for which a child is vaccinated with DPT?
Answer:
DPT is vaccine for diphtheria, whooping cough and tetanus.

Question 3.
Which body cells contribute to the immunity against the infection?
Answer:
WBC, particularly the phagocytes and lymphocytes.

Question 4.
Which diseases are more fatal, acute or chronic? Why?
Answer:
Acute diseases are more fatal than chronic because of their quick manifestations.

Question 5.
Give three examples of each the followings:
(a) Waterborne disease
(b) Airborne disease
(c) STD
Answer:
(a) Typhoid, cholera and jaundice.
(b) Tuberculosis, influenza and common cold
(c) AIDS, syphilis and gonorrhea

Question 6.
Give three examples of each of the followings:
(a) Viral disease
(b) Bacterial diseases
(c) Protozoan diseases
Answer:
Viral diseases: Chickenpox, polio and measles Bacterial disease: Typhoid, cholera and tuberculosis Protozoan diseases : Malaria, sleeping sickness and kala-azar

Question 7.
Give three examples of each of the followings:
(a) Disease transmitted by water
(b) Diseases transmitted by air
(c) Diseases transmitted by vector
Answer:
(a) Cholera, typhoid and jaundice.
(b) Tuberculosis, meningitis and polio.
(c) Malaria, Sleeping sickness and dengue.

Question 8.
Name the nutrients which contribute to the body’s immunity.
Answer:
Vitamins and minerals

Question 9.
Which disease you expect a person to suffer from if he joins an overcrowded place?
Answer:
Airborne disease

Question 10.
Which is the commonly found element in the most of antibiotics?
Answer:
Sulphur

Short Answer Type Questions

Question 1.
What do you mean by health?
Answer:
Health is a state of being well enough to function well physically, mentally and socially and not merely the absence of disease. In order to keep good health, we need to take food full of nutrients, maintain good personal and domestic hygiene and regular exercise, sleep and relaxation. Our social environment and public cleanliness is also necessary for good individual health.

Question 2.
What do you mean by a disease?
Answer:
The word disease mean disturbed ease or not at ease. Disease literally means being uncomfortable. When we talk of a disease, we find a specific and particular cause for discomfort.

Question 3.
Is it possible to be in poor health without actually suffering from a particular disease?
Answer:
Yes, it is possible for a person to be in a poor health without actually suffering from a particular disease. Simply not being diseased is not same as being healthy. In order to keep healthy, we need to be happy if we mistreat each other or are afraid of each other, we can not be healthy. Good health for a dancer means he should be able to stretch his body into different but graceful positions. If the dancer is not suffering from any disease but he is not able to stretch his body according to the dance, he will not be considered in a good health.

Question 4.
How do we know that there is a disease?
Or
How do we know that there is something wrong with the body?
Answer:
When there is a disease, either the functioning or the appearance of one or more system of the body will change for the worse. These changes give rise to symptoms and sign of disease. So, a headache, cough, loose motion and wound with pus are all symptoms. These indicate that there may be a disease.

Signs of disease are what physicians will look for on the basis of symptoms. Signs will give a little indication of presence of a disease. Physician will also get laboratory tests done to pinpoint the disease further.

Question 5.
What are acute and chronic diseases? Give examples.
Answer:
Acute diseases: The diseases which last for a short periods of time, are called acute diseases. example : Common cold, influenza, typhoid fever, cholera etc. These diseases if not treated well in time can be fatal. Chronic diseases: Some diseases which last for a long time i.e. one year or more or in’ some cases even as much as lifetime. Examples : Tuberculosis, elephantitis, AIDS, cancers etc. Chronic disease causes prolonged general poor health.

Question 6.
A baby is suffering from loose motions. What are the immediate and contributory causes?
Answer:

• The immediate cause of loose motions is an infection with a virus or bacteria.
• The lack of good nourishment or poor nourishment and genetic difference are the other contributory causes of the disease. Because without virus, the genetic difference and poor nourishment alone would not lead to loose motions.
• The poor public services such as supply of uncleaned drinking water in the area where the family lives, is the third possible cause of disease.

Question 7.
What are infectious diseases and non infectious diseases? Give examples?
Answer:
Infectious diseases. Diseases where microorganism or microbes are the immediate causes are called inflectious diseases. This is because these microbes can spread in the community, and the diseases they cause will spread with them. Example: common cold, influenza, dengue fever, cholera, tuberculosis and anthrax etc.

Non-infectious diseases: These are diseases that are neither caused by infectious agents like microbes nor can spread in the community. Instead, the cause of disease are mostly internal i. e. malfunctioning of body organs.
Example : High blood pressure, Cancer, Stones in different body organs, etc.

Question 8.
Name the different diseases caused by the following organisms.
Answer:

Question 9.
How does cholera spread from an infected person to a healthy person?
Answer:
Cholera spread from one person to another through water. This occurs if tire excreta from one person suffering from cholera, get mixed with drinking water used by the other healthy people living nearby. The cholera causing microbe Vibrio cholerae will enter new host through the water, they drink and cause disease in them.

Question 10.
How is the AIDS transmitted from one person to another?
Answer:
AIDS is transmitted from a person to another by the following ways,

• By sexual contact from an infected partner to another.
• The AIDS virus can also spread through blood-to-blood contact with infected person.
• It can also spread from an infected mother to her baby during pregnancy or through breastfeeding.

Question 11.
Give some ways in which AIDS does not spread from one person to another.
Answer:
AIDS does not spread from one person to another in the following ways.
AIDS is not transmitted by handshakes or hugs or sports like wrestling, or by any of the other ways, we touch each other socially.

Question 12.
How does malaria spread from one person to another person?
Answer:
Malaria spread from infected person to healthy person by the bite of a female anopheles mosquito. These insects carry the infecting agent plasmodium from sick person to another healthy person and transfer disease from person to person.

Question 13.
What are air borne diseases? Give examples.
Answer:
The diseases which spread from infected person to healthy person through air are called air borne diseases. For example. Common cold, pneumonia and tuberculosis.

Question 14.
How do the sign and symptoms of a disease depend upon the organ affected by microbes? Explain with example.
Answer:
The signs and symptoms depends upon the tissues or organ which the microbe targets. For example if the lungs are targeted, then symptoms will be cough and breathlessness. If the liver is targeted, there will be jaundice. If the brain is the target, we will observe headache, vomiting, fits or unconsciousness.

Question 15.
What is AIDS? What is die cause of this disease? What are effects of HIV-AIDS?
Answer:
AIDS (Acquired Immuno Deficiency Syndrome) is a chronic fatal disease in which immune system of the body is seriously affected. The cause of this disease is a virus which is known as HIV (Human Immuno Deficiency Virus). Many effects of HIV-AIDS are because the body can no longer fight off the many minor infections that we face everyday. Instead, every small cold can become pneumonia. Similarly minor gut infections can produce major diarrhoea, with blood loss. Ultimately, it is these other infections that kill person suffering from HIV-AIDS.

Question 16.
How does the severity of disease manifestations depend upon number of microbes in the body?
Answer:
The severity of disease depends upon the number of microbes in the body. If the number of microbes is very small, the disease manifestations may be minor, or may go unnoticed. But if the number of microbes is very large, the disease can be severe enough to be life threatening.

Question 17.
Explain why is it harder to make antiviral medicines than antibacteria medicines.
Answer:
One reason why making antiviral medicines is harder than making anti bacterial medicines is that viruses have few biochemical mechanisms of their own. They enter our cells and use our machinery for their life processes. This means there are few virus specific targets to aim at. But bacterial synthesis pathways are different from that used by our cells. So we can easily find a drug that blocks the multiplication of bacteria without affecting our body. This is achieved by antibiotics.

Question 18.
Why is prevention of diseases better than their cure? Give three reason.
Answer:
Prevention of diseases is better than their cure because

1. If someone has a disease, their body functions are damaged and may never recover completely.
2. The treatment of disease will take time, which means that person suffering from a disease is likely tube Wed ridden for sometime even if we can give proper treatment.
3. The disease, from which a person is suffering, may spread to other person.

Question 19.
What type of drugs should be given to a patient suffering from diseases caused by bacteria and why?
Answer:
Antibiotics should be given to a patient suffering from diseases caused by bacteria because they commonly blocks the biochemical pathways important for bacteria. Bacteria make cell-wall to protect themselves. The antibiotic penicillin blocks the bacterial processes that build the cell-wall. As a result growing bacteria became unable to make cell-walls and die easily.

Question 20.
What type of diseases are caused by the following.
(a) If lungs are infected by bacteria.
(b) If liver is infected by virus.
(c) If brain is infected by the virus.
Answer:
(a) Tuberculosis.
(b) Jaundice.
(c) Japanese encephalitis or meningitis.

Question 21.
What are the principles of treatment?
Answer:
The principles of treatment are as follows:

1. First the doctor should know the cause of the diseases by examining the patient.
2. The doctor should provide treatment that reduce the effect of the disease.
3. The doctor should prescribe drugs which can kill the microbes or stop the proliferation of disease causing microbes.

Question 22.
What are two general ways to prevent diseases.?
Answer:
General ways to prevent diseases are as follows:

1. By preventing exposure to infectious microbes.
2. The second basic principle of prevention of infection disease is the availability of proper and sufficient food for everyone, so that the functioning of the immune system remain good.

Question 23.
What is the specific way of preventing infectious diseases?
Answer:
The specific way of prevention of infectious disease is to strengthen the immune system of the body by giving some vaccines. Many vaccines are now available for preventing a whole range of inflections diseases and provide a disease specific means of preventions. There are vaccines against tetanus, diphtheria, measles, polio and many others.

Question 24.
There is a vaccine for hepatitis A, in the market. But the majority of children in many parts of India are already immune to hepatitis A by the time they are five years old? Why is it so?
Answer:
Some hepatitis viruses, which cause jaundice are transmitted through water. The majority of the children in many parts of India are exposed to the hepatitis A virus through water the time they are five years old. So, they become immune to hepatitis A.

Question 25.
If you had chickenpox once, there is no chance of suffering from it again. Why?
Answer:
This happens because when the immune system first sees an infectious agent or microbe, it responds against it and then remembers it specifically. So, the next time that particular microbe, or its close relatives enter the body, the immune system responds with even greater vigour. This eliminates the infection even more quickly then the first time around. So, having the disease once is a means of preventing subsequent attacks of the same disease.

Question 26.
Name the physician who discovered the vaccine against smallpox and cowpox?
Answer:
English physician named Edward Jenner, discovered the vaccine against smallpox. Dr. Jenner realised that milkmaids who had cowpox did not catch the smallpox even during epidemics. Cowpox is a very mild disease. Jenner tried deliberately giving cowpox virus to the people and found that they were now resistant to smallpox. This was because smallpox virus is closely related to cowpox virus. In this way Dr. Jenner discovered the vaccine against smallpox.

Long Answer Type Questions

Question 1.
Why do we fall ill? What does disease look like.
Answer:
There are many tissues in the body. These tissues make up organ systems that carry out body functions. Each of the organ systems has specific organs as its parts, and it has particular functions. For example digestive system has the stomach and intestine, and it helps to digest food taken in from outside the body. The musculoskeletal system, which is made up of bones and muscles, holds the body parts together and helps the body move.

When there is any disease either the functioning or the appearance of one or more systems of the body will change for the worse. These changes give rise to symptoms and sign of diseases. Symptoms of disease are the things we feel as being wrong, i.e, if our digestive system is not good, we have loose motion or constipation or pain in the stomach or some gastric trouble.

If our lungs are infected than we loose our weight, become short of breath, feel tired all the time, have fever, cough. These symptoms indicate the tuberculosis of lungs. If we have headache it means just examination stress for any other type of stress or, very rarely, it may mean meningitides or any of the other disease on the basis of certain laboratory test.

Only symptoms do not indicate what the disease is. On the basis of symptoms, the physician get laboratory test i.e. blood sugar, blood pressure, x-ray of a certain organ etc. to pinpoint the disease further.

Question 2.
What do you mean by the (a) immediate cause and (b) contributory cause of a particular disease ? Explain with the help of an example.
Answer:
There are many causes of a particular disease. These causes inlude:
(a) Immediate cause. Immediate cause of a particular disease may be a infectious agents mostly microorganism such as virus, bacteria, worms or protozoans etc. The disease where microbes are the immediate cause are called infectious diseases.

In some diseases immediate cause are not infectious agent such as some cancer. These are caused by genetic abnormalities or heart diseases caused by malfunctioning of heart.

(b) Contributory causes. The microbes can spread in the community due to unhygienic condition or poor nourishment. Thus, unhygienic conditions, poor nourishment are the contributory causes.

Example. If there is baby suffering from loose motions, we can say that the cause of the loose motions is an infection with a virus. So, the immediate cause of the disease is a virus. We find that this virus came through unclean drinking water. But many babies must have had this unclean water. So, why is it that only one baby developed loose motion while the other babies did not.

One reason for the infection is that baby is not healthy because he is not well nourished and does not get balanced diet. So, genetic difference, lack of good nourishment and unclean drinking water are contributory causes of loose motion. Without the virus, the poor nourishment or genetic difference alone may not lead to loose motion.

Question 3.
What are the different types of infectious micro-organisms which cause infectious diseases? Also give the diagrams and the diseases caused by some of these organisms.
Answer:
Organism that can cause disease are found in a wide range of categories of classification. Some of these are viruses, bacteria, fungi, single-celled animals or protozoans and worms of different kind.

(i) Virus: All virus live inside host cells and multiply very quickly. The diseases caused by viruses are common cold, influenza, dengue fever SARS and AIDS.
The picture of the SARS virus coming out of the surface of an infected cell is shown below.

(ii) Bacteria: Bacteria are organism which are closely related to each other which means many important life process are similar in the bacteria group. Diseases like typhoid fever, cholera, tuberculosis and anthrax are caused by bacteria.

The picture of staphylococci, the bacteria which can cause acne, is shown below.

(iii) Protozoans: Protozoans are single celled animals. These microbes causes many familiar diseases such as malaria and kala-azar. Some protozoa also cause sleeping sickness. The protozoa, leishmania is shown in the figure causes kalaazar. The organism is oval shaped and each has one long whip-like structure.

(iv) Worms: Some worms like roundworm, tapeworm live in the intestine. Ascariasis and Taeniasis diseases are caused by the roundworm and tapeworm respectively. The disease elephantiasis is also caused by a species of worms.
The pictures below shows the roundworm. This type of roundworm live in small intestine.

Question 4.
How do infectious diseases spread from infected person to healthy person? Give any four ways with examples.
Answer:
Many microbial agents can commonly move from an affected person to someone else (healthy person) in different ways. These diseases can be communicated from one person to another, so these diseases are called communicable diseases. These communicable diseases can spread by the following ways.

(i) By air. Common cold, preumonia and tuberculosis spread through air from one person to another. This occurs through the little droplets thrown out by an infected person who sneezes or coughs. Some one standing close by can breathe in these droplets and the microbes get a chance to start new infection. Obviously, the more crowded our living conditions are, the more likely it is that such air bone diseases will spread.

(ii) By water. The diseases like cholera, jaundice spread through water. This occurs if the excreta from some one suffering from an infectious disease, such as cholera, get mixed with the drinking water used by the people living nearby. The cholera causing microbes will enter new hosts through the water they drink and cause diseases in them.

(iii) By sexual contact. Some diseases like HIV- AIDS are transmitted by sexual contact from one partner to the other. However, such sexually transmitted diseases do not spread by physical contact such as hand shakes or hugs or sports like wrestlings.

(iv) By Blood to Blood contact: The AIDS virus can also spread through blood-to-blood contact from an infected people. It can also spread from an infected mother to her baby through breast feeding or during pregenancy.

(v) By other creature or animals. Many diseases are transmitted from infected people to the other healthy people through other animals. These animals carry the infecting agents from a sick person to another potential host or healthy person. These animals are called vectors.

The commonest vectors are mosquitoes. The female mosquitoes need highly nutritious food in the form of blood in order to be able to lay mature eggs. Thus, the malaria causing microbes entering through a mosquito bite, will go to the liver and then to the red blood cells. The virus causing Japanese encephalitis or brain fever also enter through mosquito bite.

Question 5.
What are the principles of treatment of infectious diseases? Explain with the help of examples.
Answer:
There are two ways to treat an infectious diseases:
(i) One would be to reduce the effect of the disease; we can provide the treatment that will reduce the symptoms. The symptoms are usually because of inflammation. For example, we can take medicine that bring down the fever, reduce pain or loose motions. We can take bed rest so that we can conserve our energy. But this kind of symptom-directed treatment by itself will not make the infecting microbes go away and the disease will not be cured.

(ii) The second way is to use medicine that kill the microbes which are main cause of disease. Microbe are classified in different categories. As each groups of microbes have some essential biochemical life process which is peculiar to that group and not shared with the other group. These pathways or processes are not used by us either.

For example : Our cells may make new substances by a mechanism different from that used by the bacteria or virus. We have to find a drug that blocks the bacterial synthesis pathway without affecting our own. The antibiotic drugs blocks the synthesis pathways related to the bacteria. Similarly, there are drugs which kill the protozoa such as malarial parasite. There are antiviral drugs also which can keep HIV infection under control.

Question 6.
What are the principles of preventing infectious diseases?
Answer:
The principles of preventing infectious diseases are as follows:
1. The general way of preventing infectious diseases mostly relate to the preventing of exposure to the infectious microbes.

For Example: In case of airborne microbes, we can prevent ourselves by providing living condition that are not over crowded. For water home microbes, we can prevent exposure by providing safe drinking water. The. drinking water should be filtered and free from any microbial contamination.

For vector-borne diseases, we require clean environment or we can say that the public hygiene is the basic key to prevention of infectious diseases. Clean environ-ment would not allow any mosquito breeding. We can prevent the spreading of disease like malaria and Japanese fever etc.

2. The second basic principle of prevention of infectious diseases is the availability of proper and sufficient food for everyone. The functioning of our immune system in our body will not be good if proper and sufficient nourishment food is not available. The immune cell manage to kill the microbes. If the number of infecting microbes are controlled, the manifestation of disease will be minor.

3. The infectious diseases can be prevented by immunisation. In general, we befool the immune systems to develop a memory for a particular infection by putting something, that mimic the microbes we want to vaccinate against, into the body. This does not actually cause the disease but this would prevent any subsequent exposure to the infecting microbe from turning into actual disease.

Many such vaccines e.g. vaccines against tetanus, diptheria, measles, polio etc. are available. These provide a disease-specific means of prevention.

These NCERT Solutions for Class 9 Science Chapter 12 Sound Questions and Answers are prepared by our highly skilled subject experts to help students while preparing for their exams.

Sound NCERT Solutions for Class 9 Science Chapter 12

Class 9 Science Chapter 12 Sound InText Questions and Answers

Question 1.
How does the sound produced by a vibrating object in a medium reach your ear?
Answer:
When an object vibrates, it forces the neighbouring particles of the medium to vibrate. These vibrating particles then force the particles adjacent to them to vibrate. In this way, vibrations produced by an object are transferred from one particle to another till it reaches the ear.

Question 2.
Explain how sound is produced by your school bell.
Answer:
When the school bell vibrates, it forces the adjacent particles in air to vibrate. This disturbance gives rise to a wave and when the bell moves forward, it pushes the air in front of it. This creates a region of high pressures known as compression. When the bell moves backwards, it creates a region of low pressure know as rarefaction. As the bell continues to move forward and backward, it produces a series of compressions and rarefactions. This makes the sound of a bell propagate through air.

Question 3.
Why are sound waves called mechanical waves?
Answer:
Sound waves force the medium particles to vibrate. Hence, these waves are known as mechanical waves. Sound waves propagate through a medium because of the interaction of the particles present in that medium.

Question 4.
Suppose you and your friend are on the moon. Will you be able to hear any sound produced by your friend?
Answer:
Sound needs a medium to propagate. Since the moon is devoid of any atmosphere, you cannot hear any sound on the moon.

Question 5.
Distinguish between loudness and intensity of sound.
Answer:
Intensity of a sound wave is defined as the amount of sound energy passing through a unit area per second. Loudness is a measure of the response of the ear to the sound. The loudness of a sound is defined by its amplitude. The amplitude of a sound decides its intensity, which in turn is perceived by the ear as loudness.

Question 6.
How are the wavelength and frequency of a sound wave related to its speed?
Answer:
Speed, wavelength, and frequency of a sound wave are related by the following equation:
Speed (v) = Wavelength (λ) × Frequency (u)
v = λ × u

Question 7.
Calculate the wavelength of a sound wave whose frequency is 220 Hz and speed is 440 m/s in a given medium.
Ans. Frequency of the sound wave, υ = 220 Hz
Speed of the sound wave, v = 440 m s^-1
For a sound wave,
Speed = Wavelength × Frequency
v = λ × u
∴ λ = \(\frac{v}{u}=\frac{440}{220}\) = 2 m
Hence, the wavelength of the sound wave is 2m.

Question 8.
A person is listening to a tone of 500 Hz sitting at a distance of 450 m from the source of the sound. What is the time interval between successive compressions from the source?
Answer:
The time interval between two successive compressions is equal to the time period of the wave. This time period is reciprocal of the frequency of the wave and is given by the relation:
T = \(\frac{1}{\text { Frequency }}=\frac{1}{500}\) = 0.002s

Question 9.
In which of the three media, air, water or iron, does sound travel the fastest at a particular temperature?
Answer:
The speed of sound depends on the nature of the medium. Sound travels the fastest in solids. Its speed decreases in liquids and it is the slowest in gases.
Therefore, for a given temperature, sound travels fastest in iron.

Question 10.
An echo returned in 3s. What is the distance of the reflecting surface from the source, given that the speed of sound is 342 ms^-1?
Answer:
Speed of sound, v = 342 ms^-1
Echo returns in time, t = 3s
Distance travelled by sound = v × t = 342 × 3 = 1026 m
In the given time interval, sound has to travel a distance that is twice the distance of the reflecting surface and the source.
Hence, the distance of the reflecting surface from the source = \(\frac{1026}{2}\) m = 513 m

Question 11.
Why are the ceilings of concert halls curved?
Answer:
Ceilings of concert halls are curved so that sound after reflection (from the walls) spreads uniformly in all directions.

Question 12.
What is the audible range of the average human ear?
Answer:
The audible range of an average human ear lies between 20 Hz to 20,000 Hz. Humans cannot hear sounds having frequencies less than 20 Hz and greater than 20,000 Hz.

Question 13.
What is the range of frequencies associated with
(a) Infrasound?
(b) Ultrasound?
Answer:
(a) Infrasound has frequencies less than 20 Hz.
(b) Ultrasound has frequencies more than 20,000 Hz.

Question 14.
A submarine emits a sonar pulse, which returns from an underwater cliff in 1.02 s. If the speed of sound in saltwater is 1531 m/s, how far away is the cliff?
Answer:
Time taken by the sonar pulse to return, t = 1.02 s
Speed of sound in saltwater, v = 1531 ms^-1
Total distance covered by the sonar pulse = Speed of sound × Time taken
Total distance covered by the sonar pulse
= 1.02 × 1531 = 1561.62 …..(i)
Let d be the distance of the cliff from the submarine.
Total distance covered by the sonar pulse = 2d
⇒ 2d = 1561.62 [From(i)]
⇒ d = 780.81 m

Class 9 Science Chapter 12 Sound Textbook Questions and Answers

Question 1.
What is sound and how is it produced?
Answer:
Sound is produced by vibration. When a body vibrates, it forces the neighbouring particles of the medium to vibrate. This creates a disturbance in the medium, which travels in the form of waves. This disturbance, when reaches the ear, produces sound.

Question 2.
Describe with the help of a diagram, how compressions and rarefactions are produced in air near a source of sound.
Answer:
When a vibrating body moves forward, it creates a region of high pressure in its vicinity. This region of high pressure is known as compressions. When it moves backward, it creates a region of low pressure in its vicinity. This region is known as a rarefaction. As the body continues to move forward and backwards, it produces a series of compressions and rarefactions (as shown in the following figure).

Question 3.
Cite an experiment to show that sound needs a material medium for its propagation.
Answer:
Take an electric bell and hang this bell inside an empty bell-jar fitted with a vacuum pump (as shown in the following figure).

Initially, one can hear the sound of the ringing bell. Now, pump out some air from the bell-jar using the vacuum pump. It will be observed that the sound of the ringing bell decreases. If one keeps on pumping the air out of the bell-jar, then at one point, the glass-jar will be devoid of any air. At this moment, no sound can be heard from the ringing bell although one can see that the prong of the bell is still vibrating. When there is no air present inside, we can say that a vacuum is produced. Sound cannot travel through vacuum. This shows that sound needs a material medium for its propagation.

Question 4.
Why is sound wave called a longitudinal wave?
Answer:
The vibration of the medium that travels along or parallel to the direction of the wave is called a longitudinal wave. In a sound wave, the particles of the medium vibrate in the direction parallel to the direction of the propagation of disturbance. Hence, a sound wave is called a longitudinal wave.

Question 5.
Which characteristics of the sound helps you to identify your friend by his voice while sitting with others in a dark room?
Answer:
Quality of sound is that characteristic which helps us identify a particular person. Sound produced by two persons may have the same pitch and loudness, but the quality of the two sounds will be different.

Question 6.
Flash and thunder are produced simultaneously. But thunder is heard a few seconds after the flash is seen, why?
Answer:
The speed of sound (344 m/s) is less than the speed of light (3 × 10⁸ m/s). Sound of thunder takes more time to reach the Earth as compared to light. Hence, a flash is seen before we hear a thunder.

Question 7.
A person has a hearing range from 20 Hz to 20 kHz. What are the typical wavelengths of sound waves in air corresponding to these two frequencies? Take the speed of sound in air as 344 ms^-1.
Answer:
For a sound wave,
Speed = Wavelength × Frequency
v = λ × υ
Given that the speed of sound in air = 344 m/s
(j) For, υ = 20.Hz
λ1 = \(\frac{v}{v_{1}}=\frac{344}{20}\) = 17.2m
(ii) For, υ₂ = 20,000 Hz
λ₂ = \(\frac{v}{v_{2}}=\frac{344}{20,000}\) = 0.0172 m
Hence, for humans, the wavelength range for hearing is 0.0172 m to 17.2 m.

Question 8.
Two children are at opposite ends of an aluminium rod. One strikes the end of the rod with a stone. Find the ratio of times taken by the sound wave in air and in aluminium to reach the second child.
Answer:
Let the length of the aluminium rod be d.
Speed of sound wave in aluminium at 25°C,
v_Al = 6420 ms^-1
Therefore, time taken by the sound wave to reach the other end,
\(t_{\mathrm{Al}}=\frac{d}{v_{\mathrm{Al}}}=\frac{d}{6420}\)
Speed of sound wave in air at 25°C, vAir = 346 ms^-1 .
Therefore, time taken by sound wave to reach the other end,
\(t_{\text {Air }}=\frac{d}{v_{\text {Air }}}=\frac{d}{346}\)
The ratio of time taken by the sound wave in air and aluminium: \(\frac{t_{\text {Air }}}{t_{\mathrm{Al}}}=\frac{\frac{d}{346}}{\frac{d}{6420}}=\frac{6420}{346}=18.55\)

Question 9.
The frequency of a source of sound is 100 Hz. How many times does it vibrate in a minute?
Answer:
Frequency is defined as the number of oscillations per second. It is given by the relation:
Frequency = \(\frac{\text { Number of oscillations }}{\text { Total Time }}\)
Number of oscillations = Frequency × Total time
Given, Frequency of sound = 100 Hz
Total time = 1 min = 60 s
Number of oscillations / Vibrations = 100 × 60 = 6000
Hence, the source vibrates 6000 times in a minute, producing a frequency of 100 Hz.

Question 10.
Does sound follow the same laws of reflection as light does? Explain.
Answer:
Sound follows the same laws of reflection as light does. The incident sound wave and the reflected sound wave make the same angle with the normal to the surface at the point of incidence. Also, the incident sound wave, the reflected sound wave, and the normal to the point of incidence all lie in the same plane.

Question 11.
When a sound is reflected from a distant object, an echo is produced, Let the distance between the reflecting surface and the source of sound production remains the same. Do you hear echo sound on a hotter day?
Answer:
An echo is heard when the time interval between the original sound and the reflected sound is at least 0.1 s. The speed of sound in a medium increases with an increase in temperature. Hence, on a hotter day, the time interval between the original sound and the reflected sound will decrease. Therefore, an echo can be heard only if the time interval between the original sound and the reflected sound is greater than 0.1 s.

Question 12.
Give two practical applications of reflection of sound waves.
Answer:

• Reflection of sound is used to measure the distance and speed of underwater objects. This method is known as SONAR.
• Working of a stethoscope is also based on reflection of sound. In a stethoscope, the sound of the patient’s heartbeat reaches the doctor’s ear by multiple reflection of sound.

Question 13.
A stone is dropped from the top of a tower 500 m high into a pond of water at the base of the tower. When is the splash heard at the top? Given, g=10 ms^-2and speed of sound = 340 ms^-1.
Answer:
Height of the tower, s = 500 m
Velocity of sound, v = 340 ms^-1
Acceleration due to gravity, g = 10 ms^-2
Initial velocity of the stone, u = 0 (since the stone is initially at rest)
Time taken by the stone to fall to the base of the tower, t₁

According to the second equation of motion:
s = ut1 + \(\frac {1}{2}\)gt₁²
500 = 0 × t1 + \(\frac {1}{2}\) × 10 × t₁²
r₁² = 100
t₁ = 10 s
Now, time taken by the sound to reach the top from the base of the tower, t₂ = \(\frac {500}{340}\) = 1.47S
Therefore, the.splash is heard at the top after time, t
Where, t = t₁ + t₂ = 10 + 1.47 = 11.47 s

Question 14.
A sound wave travels at a speed of 339 ms^-1. If its wavelength is 1.5 cm, what is the frequency of the wave? Will it be audible?
Answer:
Speed of sound, v = 339 ms^-1
Wavelength of sound, λ = 1.5 cm = 0.015 m
Speed of sound = Wavelength × Frequency
v = λ × υ
∴ υ = \(\frac{v}{\lambda}=\frac{339}{0.015}\) = 22600 Hz
The frequency range of audible sound for humans lies between 20 Hz to 20,000 Hz. Since the frequency of the given sound is more than 20,000 Hz, it is not audible.

Question 15.
What is reverberation? How can it be reduced?
Answer:
Persistence of sound (after the source stops producing sound) due to repeated reflection is known as reverberation. As the source produces sound, it starts travelling in all directions. Once it reaches the wall of a room, it is partly reflected back from the wall. This reflected sound reaches the other wall and again gets reflected partly. Due to this, sound can be heard even after the source has ceased to produce sound.

To reduce reverberations, sound must be absorbed as it reaches the walls and the ceiling of a room. Sound absorbing materials like fibre board, rough plastic, heavy curtains, and cushioned seats can be used. to reduce reverberation.

Question 16.
What is loudness of sound? What factors does it depend on?
Answer:
A loud sound has high energy. Loudness depends on the amplitude of vibrations. In fact, loudness is proportional to the square of the amplitude of vibrations.

Question 17.
Explain how bats use ultrasound to catch a prey.
Answer:
Bats produce high-pitched ultrasonic squeaks. These high-pitched squeaks are reflected by objects such as preys and returned to the bat’s ear. This allows a bat to know the distance of his prey.

Question 18.
How is ultrasound used for cleaning?
Answer:
Objects to be Cleansed are put in a cleaning solution and ultrasonic sound waves are passed through that solution. The high frequency of these ultrasound waves detaches the dirt from the objects.

Question 19.
Explain the working and application of a sonar.
Answer:
SONAR is an acronym for Sound Navigation And Ranging. It is an acoustic device used to measure the depth, direction, and speed of underwater objects such as submarines and shipwrecks with the help of ultrasounds. It is also used to measure the depth of seas and oceans.

A beam of ultrasonic sound is produced and transmitted by the transducer (it is a device that produces ultrasonic sound) of the SONAR, which travels through seawater. The echo produced by the reflection of this ultrasonic sound is detected and recorded by the detector, which is converted into electrical signals. The distance (d) of the under-water object is calculated from the time (f) taken by the echo to return with speed (v) is given by 2d = v × t. This method of measuring distance is also known as ‘echo-ranging’.

Question 20.
A sonar device on a submarine sends out a signal and receives an echo 5 s later. Calculate the speed of sound in water if the distance of the object from the submarine is 3625 m.
Answer:
Time taken to hear the echo, t = 5s
Distance of the object from the submarine, d = 3625 m
Total distance travelled by the sonar waves during the transmission and reception in water = 2d
Velocity of sovmd in water,
v = \(\frac{2 d}{t}=\frac{2 \times 3625}{5}\) = 1450 ms^-1

Question 21.
Explain how defects in a metal block can be detected using ultrasound.
Answer:
Defects in metal blocks do not allow ultrasound to pass through them and they are reflected back. This fact is used to detect defects in metal blocks. Ultrasound is passed through

one end of a metal block and detectors are placed on the other end. The defective part of the metal block does not allow ultrasound to pass through it. As a result, it will not be detected by the detector. Hence, defects in metal blocks can be detected using ultrasound.

Question 22.
Explain how the human ear works.
Answer:
Different sounds produced in our surroundings are collected by pinna that sends these sounds to the eardrum via the ear canal. The eardrum starts vibrating back and forth rapidly when the sound waves fall on it. The vibrating eardrum sets the small bone hammer into vibration. The vibrations are, passed from the hammer to the second bone anvil, and finally to the third bone stirrup. The vibrating stirrup strikes on the membrane of the oval window and passes its vibration to the liquid in the cochlea. This produces electrical impulses in nerve cells. The auditory nerve carries these electrical impulses to the brain. These electrical impulses are interpreted by the brain as sound and we get a sensation of hearing.

Class 9 Science Chapter 12 Sound Additional Important Questions and Answers

Multiple choice Question
Choose the correct option:

Question 1.
Note is a sound
(a) of mixture of several f.requencies
(b) of mixture of two frequencies only
(c) of a single frequency
(d) a ways unpleasant to listen
Answer:
(c) of a single frequency

Question 2.
A key of a mechanical piano struck gently and then struck again but much harder this time. In the second case
(a) sound will be louder but pitch will not be different
(b) sound will be louder and pitch will also be higher
(c) sound will be louder but pitch will be lower
(d) both loudness and pitch will remain unaffected
Answer:
(a) sound will be louder but pitch will not be different

Question 3.
In SONAR, we use
(a) ultrasonic waves
(b) infrasonic waves
(c) radio waves
(d) audible sound waves
Answer:
(a) ultrasonic waves

Question 4.
Sound travels in air if
(a) particles of medium travel from one place to another
(b) there is no moisture in the atmosphere
(c) disturbance moves
(d) both particles as well as disturbance travel from one place to another.
Answer:
(c) disturbance moves

Question 5.
When we change feeble sound to loud sound we increase its
(a) frequency
(b) amplitude
(c) velocity
(d) wavelength
Answer:
(b) amplitude

Question 6.
In the curve (Fig.12.1) half the wavelength is

Answer:
(b)

Question 7.
Earthquake produces which kind of sound before the main shock wave begins
(a) ultrasound
(b) infrasound
(c) audible sound
(d) none of the above
Answer:
(b) infrasound

Question 8.
Infrasound can be heard by
(a) dog
(b) bat
(c) rhinoceros
(d) human beings
Answer:
(c) rhinoceros

Question 9.
Before playing the orchestra in a musical concert, a sitarist tries to adjust the tension and pluck the string suitably. By doing so, he is adjusting
(a) intensity of sound only
(b) amplitude of sound only
(c) frequency of the sitar string with the frequency of other musical instruments
(d) loudness of sound
Answer:
(c) frequency of the sitar string with the frequency of other musical instruments

Very Short Answer Questions

Question 1.
What is sound?
Answer:
It is a form of energy that enables us to hear.

Question 2.
What is necessary for a body to produce sound?
Answer:
The vibrating bodies can only produce sound.

Question 3.
Which three parameters are used to describe sound?
Answer:
The three parameter used to describe sound are amplitude, frequency and quality.

Question 4.
What determines the loudness of a sound wave?
Answer:
Amplitude determines the loudness of a sound.

Question 5.
What determines the pitch of a sound.
Answer:
The frequency of sound wave determines the pitch.

Question 6.
What are two types of mechanical wave motions?
Answer:
The two types of mechanical wave motions ate transverse waves and longitudinal waves.

Question 7.
Name the wave motion in which the wave propagates in the direction of motion.
Answer:
In longitudinal wave motion, the waves propagate in the direction of motion.

Question 8.
Why is sound wave called a mechanical wave?
Answer:
Sound cannot travel through vacuum, it requires the presence of a medium for its propagation.

Question 9.
In which physical medium, the sound travels the fastest?
Answer:
Sound travels the fastest in solids.

Question 10.
What are curtains and furniture in a house, good reflectors or absorbers of sound?
Answer:
They are good absorbers of the sound.

Question 11.
What do you understand by the reflection of sound?
Answer:
It refers to the bouncing back of the sound in the same medium after striking a non-absorptive solid surface.

Question 12.
Which part of human body helps produce the sound?
Answer:
The vocal cord also called Adam’s apple help produce the sound.

Question 13.
In which medium will the reflection of sound be faster, air or water?
Answer:
In water, the density of water is more than that of air and hence, the speed of sound in water is more than in air.

Question 14.
Name the property of sound, human ears respond to after hearing the sound.
Answer:
Human ears are receptive to the loudness therefore, they only respond to loudness.

Question 15.
Which property is used to distinguish two sounds from different sources but having the same amplitude and pitch ?
Answer:
The property used to distinguish the sound waves having same pitch and frequency is called quality.

Question 16.
In which form the sound waves travels across a medium.
Answer:
The sound waves travel in the form of. compression and rarefaction.

Question 17.
How is an ultrasonic wave different from the infrasonic wave?
Answer:
Infrasonic waves have the frequency less than 20Hz while the ultrasonic waves have the frequency of more than 20KHz.

Question 18.
If the speed of sound incident on a surface is doubled, will there be any effect on the angle of reflection of sound ?
Answer:
No, there will be no effect on the angle of reflection of sound because it is dependent on the angle of incidence, not on the speed of sound.

Question 19.
What will happen, if a sound wave is made incident at 90° on a solid surface?
Answer:
No reflection will occur but the development of resonance Will take place.

Question 20.
Can sound waves be transformed into » electrical impulses or vice versa?
Answer:
Yes, the sound waves can be transformed into electrical impulses or vice versa as it happens in telephone.

Question 21.
What is the law of conservation of energy?
Answer:
The law states that energy can neither be created nor be destroyed but one form of energy can be transformed into another form of energy.

Question 22.
State the energy transformations which take place when you clap your hands.
Answer:
When dapping, the muscular energy is transformed into sound and heat energy.

Question 23.
How is a light wave different from a sound wave?
Answer:
Sound wave requires a medium for its propagation but not light wave. It can even pass through a vacuum.

Question 24.
The distance in between two adjoining crest and trough is ‘d’. What is the wavelength of the wave?
Answer:
The wavelength is the distance in between two successive troughs or crests, therefore the wavelength would be 2d.

Question 25.
What do you mean by supersonic speed?
Answer:
When the speed of an object/body exceeds the speed of sound, then the speed is called supersonic speed.

Short Answer Type Questions

Question 1.
What is a wave? Can sound be visualized as a wave?
Answer:
Wave is a disturbance that moves through a medium due to repeated oscillatory motion of the particles of the medium about their mean position. This oscillatory motion is passed over from one particle to another progressively. Hence, a wave only involves the transfer of energy not particles of the material medium.

Sound is visualized as a wave because the disturbance set by the sound in the medium travel through the medium in form of energy instead of the particle of the medium.

Question 2.
What are longitudinal waves? Give an example.
Answer:
The waves in which the particles of the medium vibrate in the direction of the propagation of the wave are called longitudinal waves. During propagation of these waves, the particles of the medium only exhibit the vibratory motion along their mean position.

Sound waves propagate in the form of longitudinal waves.

Question 3.
What are transverse waves? Give an example.
Answer:
The waves in which the particles of the medium vibrate in the direction perpendicular to the direction of the propagation of wave is called transverse wave. The positive displacement from the mean position makes up the crest while the negative displacement from the mean position makes up the trough.

When a pebble is dropped in stagnant water, water ripples formed on the surface water represents the transverse waves.

Question 4.
What are mechanical and non¬mechanical waves? Give examples.
Answer:
The waves which require the presence of a material medium for their propagation are called mechanical or elastic waves e.g. sound waves. These waves can propagate through all the three states of matter but not through a vacuum.

The waves which do not require the presence of a material medium for their propagation are called non-mechanical waves or non-elastic waves e.g. light waves, microwaves or radio waves. These waves can easily propagate across the vacuum.

Question 5.
How is the loudness or softness of a sound determined? Give the wave shape of a loud and soft sound of same frequency.
Answer:
The loudness or softness of a sound depends upon its amplitude. A loud sound has higher amplitude than a soft sound when the amplitude describes the maximum displacement of the particle from its mean position.

Question 6.
The sound produced by a vehicle and a flute travels through the same medium, air and arrive at the ear at same time. Are the two sounds different? If yes, give reasons.
Answer:
No, the two sounds are different. The pitch of the sound is one of the characteristics responsible for the difference. The sound from the flute has higher frequency and has pleasing effect but the sound from vehicle has low pitch. It is cracking sound and causes irritation.

Question 7.
Different musical instruments produce different sounds. Why ?
Answer:
The different musical instruments have different modes of vibrations. These instruments with different sizes under different conditions vibrate at different frequency producing sounds of different pitches and hence, they are different from one another.

Question 8.
Give a graphical representation of for a sound wave having low pitch and high pitch.
Answer:
The pitch of a sound is determined by its frequency. Therefore, a sound with low pitch has low frequency i.e. number of the waves produced per second and sound with higher pitch has higher frequency. (Fig. 12.6).

Question 9.
In humans, whose voice is sharp, a male or female? Why?
Answer:
In humans, the voice of a female is sharper than the voice of a male because the sound produced by a female has higher frequency i.e. pitch than the sound produced by a male.

Question 10.
A person standing on the railway platform of a rural area could neither see nor hear the sound of the train. With none to help him, how can he assess the arrival time of the train?
Answer:
The person can assess the arrival time of the train by keeping his ear close to the rail line and sense the vibrations of the incoming train.

In steel, the speed of sound is 5960 m/s as compared to the speed of sound in air which is only 340 m/s. Hence, he can easily estimate the possible arrival time of the train. The fast vibration would indicate the early arrival while the slow vibrations would indicate the late arrival.

Question 11.
A person standing 1000 m away from a siren hears the sound. When will he hear the sound earlier and why?
(i) On a hot day or a calm day?
(ii) On a dry day or cloudy day having same temperature?
Answer:
(i) The person will hear the sound earlier on a hot day than on a calm day because with increasing temperature, the speed of the sound increases. At 273 K, the speed of sound is 331 m/s while at 295 k, it is 344 ms.

(ii) The person will hear the sound earlier on a cloudy day than on a dry day because the speed of the sound depends upon the density of the medium of propagation. On a cloudy day because of the presence of the moisture in air, its density is more than on a dry day.

Question 12.
What is the audible range for the human beings?
Answer:
The human ears respond to the sound waves having frequency of 20 Hz to 20 kHz. Therefore, this range of sound waves is called audible range. However, children can hear the sound up to the frequency of 25 kHz while with increasing age the range declines as old people become less sensitive to higher frequency of sound, their maximum frequency range goes up to 15,000 Hz.

Question 13.
What are infrasound and ultrasound? Give examples.
Answer:
The classification of sound waves into infrasound and ultrasound is based on the human audible range of 20 Hz to 20 kHz. The sound waves having frequency less than 20 Hz are called infra sounds and the sound waves having frequency greater than 20 kHz tire called ultrasounds.

Rhinoceros, whales and elephants can produce and respond to the infrasound waves.

Bats and rats can produce and receive ultrasound waves. Rats when playing use ultrasound waves while bats use ultrasound waves for flying in dark and capture their prey.

Question 14.
What is sonic boom? Is it harmful, if yes then give reason?
Answer:
When sound producing source moves with the speed of sound or above such as some fighter aircrafts, it produces shock wave in air. These shock waves contain a large amount of energy. The air pressure variations associated with this type of shock wave sharp and loud sound called sonic boom.

The shock waves of sonic boom possess lot of energy. They can cause the shattering of glass windows and damage the buildings.

Question 15.
What do you mean by the reflection of sound? What are the laws of reflection of sound?
Answer:
The reflection of the sound refers to the bouncing back of sound waves after being incident on a hard polished surface in the same medium.

According to the laws of the reflection of sound:

• The incident sound wave, reflected sound wave and the normal drawn at the point of incidence are in the same plane.
• The direction in which the sound is incident and is reflected make equal angle with the normal at the point of incidence.

Question 16.
What are megaphones? Why the loudness of sound is increased by megaphones?
Answer:
A megaphone is a simple horn shape tube followed by a conical opening.
In a megaphone, the sound waves from a source are reflected successively from the conical surface of the tube and directed towards audience without spreading the sound. Moreover, the amplitude of the sound waves adds up increasing the loudness of sound.

Question 17.
What is an echo? State the conditions necessary for echo formation.
Answer:
An echo refers to the reflected sound that is reheard by a speaker/listener himself. For the echo formation to occur

• there have to be a good reflective surface to reflect the sound.
• the minimum distance between the source of sound and the reflective surface has to be 17.2 m.
• there should not be any obstruction in the path of speaker and the reflective surface.

Question 18.
What is the minimum distance between the listener and the reflecting surface for hearing the distinct echo? Why?
Answer:
In humans, the time period of the persistence of sound is 0.1 second. The speed of sound in air at 295 k (22°C) is 344 m/s.

For a listener to hear a distinct echo, the reflected sound should reach his ears after a period of 0.1s.

Hence, the total distance sound of echo has to cover is = 344 × 0.1 = 34.4 m.
Therefore, the minimum distance of the reflecting surface has to be 344/2 = 17.2 m

However, this difference is temperature dependent because with the increasing temperature, the speed of the sound increases.

Question 19.
Explain why the walls and roof of the auditorium are covered with sound absorbing material?
Answer:
The walls and roof of a good auditorium are covered with sound absorbing material such as fibre boards and draperies to prevent the reverberation i.e., the repeated reflection of the sound waves. The reverberation makes the sound blurred and difficult to understand and interpret.

Question 20.
Why is the flash of lightning seen much before the thunder is heard on a rainy day, although both occur simultaneously?
Answer:
Although both lightning and thunder formation occur simultaneously at the same height in air yet the lightning flash is seen much before the hearing of thunder sound because of the difference in the speed of the sound and light The sound traveling with speed of 342 m/s takes a longer time than light traveling at the speed of 3 × 10⁸ m/s to cover the same distance.

Question 21.
State some of the practical applications of echo.
Answer:
An echo which is a reflected sound has its own applications such as

• In echo ranging or sonar, it is used to determine the depth of the oceans.
• The submarines floating in water not only measure the depth of the ocean but also the obstruction in their path in front if any.
• Bats use the echo or sound reflection in finding an obstruction free path for flying and capturing their prey.
• In medical sciences the ultrasound waves are used widely in diagnosis of structural disorders of body parts.

Question 22.
What is ultrasonography? State its use.
Answer:
Ultrasonography is a technique in which the ultrasonic waves are used to asses the structure of a body part or tissue. The ultrasound waves are made to travel through tire body tissues. Where ever there is a change in tissue density, these waves get reflected, then the reflected waves are transformed into electrical signals to generate the picture of the tissue.

The technique is widely used in examination of the growing foetus in womb of a pregnant mother and in analysis of stones in different body organs such as gall bladder, liver, etc.

Question 23.
State some of the advantages of the ultrasounds in medical sciences.
Answer:
Ultrasound consists of sound waves having frequency greater than 20 kHz. These waves are used in

• Echo-cardiography, a technique used to diagnose the blockage of heart valves or arteries.
• Creating pictures of different body organs to detect the presence of stone or any other structure like tumor.
• In breaking the small stones formed in kidney for their easy removal.

Question 24.
What is a stethoscope? On what principle does it work?
Answer:
A stethoscope is a medical instrument used by a doctor to hear the heart sounds, ‘Lub- Dub’. It’s working is based on the repeated and multiple reflection of the sound waves, received by the broad round receiver.

Question 25.
How is pressure variation in a sound wave amplified in human ear?
Answer:
The pressure vibrations produced by a vibrating object in form of compression and rarefaction reach inside the external ear and make the eardrum to vibrate. The three bones of the middle year: hammer, anvil and stirrup being solid causes the amplification of the waves by several times.

Question 26.
A longitudinal wave is produced on a toy slinky. The wave travels at the speed of 30 cm/s. If the frequency of the wave is 20 Hz. What is the minimum distance between the two consecutive compressions?
Answer:
Velocity of wave, v = 30 cm/s = 0.3 m/s
Frequency of wave, n = 20 Hz
Distance between two consecutive compressions = λ.
We know that v = λn
λ = \(\frac{v}{n}\)
\(\frac {0.30}{20}\) = 0.015 m = 15 cm

Question 27.
A child hears an echo from a cliff 4 seconds later after the sound from a powerful cracker is produced. How far away is the cliff from the child?
Answer:
Let the distance between the child and cliff = x
Total distance travelled by sound = 2x
Velocity of sound = 344 m/s
Velocity = \(\frac{\text { Distance travelled }}{\text { Time }}\)
344 = \(\frac{2 x}{4}\)
Or 2x = 688m

Question 28.
A sound wave have frequency of 2 kg Hz and wavelength of 35 cm. How long will it take to travel 1.5 km?
Answer:
Frequency, v = 2k Hz = 2000 Hz
Wavelength λ = 35 cm = 0.35 m
We know that, velocity of wave = frequency × wavelength
v = v × A.
v = 20 × 0.35 = 700 m/s
Let time taken by wave = 5 km = 1500 m
t = \(\frac{\text { Distanec travedlled }}{\text { velocity of wave }}\)
\(\frac {1500}{700}\) = 2.14 second

Question 29.
A person clapped hands near a mountain and heard the echo after 5s. What is the distance of the mountain from the person if the speed of sound at a given temperature is 346 m/s?
Answer:
Given
Speed of sound, v = 346 m/s
Time taken for hearing the echo, t = s
Let the distance between the person and mountain = x
We know that
Velocity = \(\frac{\text { Distanec travedlled }}{\text { time }}\)
346 = \(\frac{2 x}{5}\)
2x = 346 × 5 = 1730
x = \(\frac {1730}{2}\) = 865 m
Hence, distance between the person and mountain = 865 m Ans.

Question 30.
A ship sends out ultrasound produced by the transmitter that return from the sea bed and detected after 3.42s. If the speed of ultrasound through seawater is 1531 m/s. What is the distance of sea bed from the ship?
Answer:
Given
Time between transmission and detection, t = 3.42 s
Speed of the ultrasound in sea water, v = 1531 m/s
Let the distance of sea bed from ship = d
Distance travelled by ultrasound = 2 × d
We know that
v = \(\frac{\text { distance wavelength }}{\text { time taken }}\)
v = \(\frac{2 d}{t}\)
1531 = \(\frac{2 \times d}{3.42}\)
Hence, the distance of sea bed from the ship = 2618 m.

Question 31.
The frequency of a sound wave is 550 Hz. What is its wavelength? Sound travels with the a speed of 330 m/s. Calculate the time period of the wave also.
Answer:
Given
Frequency of sound wave, υ = 550 Hz
Velocity of sound wave, v = 330 m/s
Wavelength, λ = ?
λ = \(\frac{v}{υ}=\frac{330}{550}=\frac{3}{5} m\) = 0.6m
Time period = \(\frac{1}{υ}=\frac{1}{550}\)
= 0.0018 second.

Question 32.
If the velocity of sound, in a medium is 1400 m/s and its wavelength is 100m. What is its frequency? Can you hear this sound?
Answer:
Velocity of sound, v = 1400 m/s
Wavelength, λ = 100m
Frequency υ = ?
We know that, v = υ × λ
υ = \(\frac{v}{\lambda}=\frac{1400}{100}\) = 14 Hz
We can hot hear this sound, because we can hear the sound having frequency range from 20 Hz to 20000 Hz.

Question 33.
A longitudinal wave travels in a coiled spring or slinky at the rate of 4m/s. The distance between two consecutive compression is 20 cm. Find (i) wavelength of longitudinal wave (ii) frequency of longitudinal wave.
Answer:
Velocity of the longitudinal wave, v = 4 m/s
Distance between two consecutive compressions, wavelength, λ = 20 cm
= 0.2m
Frequency υ = ?
We know that
v = υ × λ.
υ = \(\frac{v}{\lambda}=\frac{4}{0.2}\) = 20 Hz

Question 34.
A body vibrating with a time period of 2 milli seconds produces a wave travelling with a velocity of 1250 m/s. What is the frequency of vibrating body? (ii) What is the wavelength of the travelling wave?
Ans.wer:
Given, Time period, T = 2 miliseconds
= 2 × 10^-3 S
Frequency, υ = \(\frac{1}{\mathrm{~T}}=\frac{1}{2 \times 10^{-3}}\) = 500Hz
Wavelenght of the wave, λ = ?
Velocity of the Wave, v = 1250 m/s
We know that
v = \(\frac{v}{υ}=\frac{1250}{500}\) = 2.5m

Question 35.
A Sonar echo takes 2.2 s to return from a whale. How far away is the whale? (Take speed of ultrasound to be 1531 m/s in seawater).
Answer:
Time taken by ultra sound between Transmission and reception, t = 2.2s
Speed of ultra sound wave, v = 1531 m/s
Depth of the whale from sea level = h
Distance travelled by ultrasound = 2 × h
We know that,
distance travelled = speed × time
2h = 1531 × 2.2
h = \(\frac{1531 \times 2.2}{2}\)
h = \(\frac{1531 \times 2.2}{2}\) = 1684.1 m
Hence, whale is 1684.1 away from the sea level

Long Answer Qestions

Question 1.
Give a simple activity to show that sound is produced by vibration.
Answer:
Suspend a smallplastic ball by a thread from a support. (Fig. 12.7) Take a tuning fork just touch, the ball with prong of the turning fork without setting it into vibration. There is no displacement in the ball. Now set the tuning fork into vibration by striking its prong with a rubber pad. Now touch the suspended ball with the prong of tuning fork. The ball get displaced from its position. Now, bring the tuning fork near your ear. You will hear sound. The ball get displaced due to thee vibration of the prong of the tuning fork. This activity shows that sound is produced due to vibration.

Fig.: Vibrating tuning fork just touching the suspended ball

Question 2.
Define speed, frequency and wavelength of a wave and derive the relation between them.
Answer:
Speed: The speed of a sound wave is defined as foe distance travelled by a point on a wave such as compression or a rarefaction in a unit time.
Speed = \(\frac{\text { distance }}{\text { time }}\)
Frequency: The number of compressions or rarefactions or crest and trough produced per unit time is known as foe frequency. It is denoted by

Wave length: The distance two consecutive compressions or rarefactions is called wavelength. It is denoted by X.
Or the distance between two consecutive crests or troughs is called wavelength.

Relation between speed, frequency and wavelength: We know that foe speed of sound wave is given by
Speed = \(\frac{\text { distance travelled by wave }}{\text { time taken }}\)
Now we known that foe wavelength (λ) is equal to foe distance travelled in one complete oscillation and foe time taken to complete one oscilaltion is called time period and is denoted by T.

Now distance travelled in time T = λ
Therefore, Speed = \(\frac{\lambda}{\mathrm{T}}\)
or v = \(\frac{\lambda}{\mathrm{T}}\) ………(i)
But we know that the frequency is the number of oscillation per unit time.
or frequency = \(\frac{1}{\text { Time Period }}\)
v = \(\frac{1}{\mathrm{~T}}\) ……….(ii)
Now putting foe value of \(\frac{1}{\mathrm{~T}}\) in equation (i) we get v = λ × \(\frac{1}{\mathrm{~T}}\)
v = λ × υ (∵ υ = \(\frac{1}{\mathrm{~T}}\))
Hence, Speed = wavelength × frequncy.

Question 3.
(i) What is reflection of sound? Prove that the reflection of sound follows the same law of reflection of light.
(ii) What are the uses of multiple reflection of sound?
Answer:
(i) Reflection of sound: When a sound wave strikes a solid or liquid surface, it is reflected back according to the laws of reflection i.e. the direction of incident and reflected sound makes equal angle with the normal to the reflecting surface and the three are in the same plane. These laws can be proved by the following activity.

Activity: Take two identical pipes as shown in the fig. 12.8. The length of the pipe should be sufficiently long (about 75 cm). Arrange them on a table near wall. Keep a clock near the open end of one of the pipes and try to hear the sound of the clock through the other pipe. Now adjust the pipes so that you can best hear the sound of the clock.

Now, measure the angle between the incident sound and the normal and the reflected sound and the normal to the reflecting surface. Now repeat the activity by changing the angles of the pipes. We find that the angle of indicent of sound wave is always equal to the angle of reflection of sound wave.

Now, becasue both the tubes are placed on the table, it also proves that incidient sound, normal and relfected sound lie th one plane.

(ii) Uses of multiple reflection of sound : (1) Megaphones or loudspeaker, horns, musical instrument such as trumpets and shehanais all designed in such a way to send sound in a particular direction. In these instruments the conical opening reflects sound successively and the amplitude of the sound wave adds up and the loudness of sound increases.
(ii) In stethoscope, the sound of heartbeat and lungs reaches the doctor’s ears by multiple reflection.
(iii) The ceilling of the conference hall and cinema halls are made curved so that sound after reflection reaches to all the corners of the halls.
(iv) Sometimes curved sound board is placed behind the stage so that sound after reflection from the sound board spread evenly across the width of the hall.

Question 4.
What are the application of ultrasound?
Answer:
The uses of ultrasound are as follows:
1. Ultrasound can be used to detect cracks and flaws in metal blocks. Ultrasonic waves are allowed to pass through the metal blocks and detectors are used to detect the transmitted wave. If there is a defect, the ultrasound gets reflected back indicating the cracks or flaws in the metal block.

2. Ultrasound scanner uses ultrasound wave for getting images of internal organs of human body such as liver, gall bladler, uterus, kidney etc. It helps the doctor for detection of stones in gall bladder and kidney and tumor in different organs. This technique is called ultrasonography. It is also used for examination of the foetus during pregnancy to detect congenial and growth abnormalities if any.

3. Ultrasound may be employed to break small stones formed in the kidneys into fine grains. These grains get flushed out with urine.

4. Ultrasound waves are made to reflect from the various parts of heart and form image of heart. This technique is called ‘Echocardiography’.

5. Ultrasound is also used to clean parts I coated in hard to reach places i.e. spiral tube, odd shapes parts of machines.