NCERT Solutions for Class 10 Science Chapter 14 Sources of Energy

These NCERT Solutions for Class 10 Science Chapter 14 Sources of Energy Questions and Answers are prepared by our highly skilled subject experts to help students while preparing for their exams.

Sources of Energy NCERT Solutions for Class 10 Science Chapter 14

Class 10 Science Chapter 14 Sources of Energy InText Questions and Answers

In-text Questions (Page 243)

Question 1.
What is a good source of energy ?
Answer:
Sun.

Question 2.
What is a good fuel ?
Answer:
A fuel which burns in air/oxygen with a moderate rate and produces a large amount of energy is called a good fuel, e.g. L.P.G.

Question 3.
If you could use any source of energy for heating your food, which one would you use and why?
Answer:
L.P.G. because it has high calorific value.

In-text Questions (Page 248)

Question 1.
What are the disadvantages of fossil fuels ?
Answer:
Disadvantages of fossil fuels :
(i) It is a non-renewable source of energy. If we were to continue consuming these courses as such fast rates, we would soon face energy crisis.

(ii) Fossil fuels cause air pollution. The oxides of carbon, nitrogen and sulphur that are released on burning fossil fuels are acidic oxides. These lead to acid rain which affects our water and soil resources.

Question 2.
Why are we looking at alternate sources of energy ?
Answer:
In ancient time, wood was the most common source of heat energy. The exploitation of coal and petroleum of energy made the industrialisation possible. The growing demand for energy was largely met by the fossil fuels, coal and petroleum. Our technologies were also developed for using these energy sources. But these fuels were formed over millions of years ago and there are only limited resources. If we were to continue consuming these sources at such alarming rates, we would soon face energy crises, In order to avoid this, we are looking at alternate source of energy.

Question 3.
How has the traditional use of wind and water energy been modified for our convenience ?
Answer:
The kinetic energy of the wind can be used to do work. This energy was harnessed, by windmills in the past to do mechanical work such as in a water lifting pump. The rotatory motion of windmill is utilised to lift water form a well. But nowadays, wind energy is used to generate electricity. To generate electricity, the rotatory motion of the windmill is used to turn the turbine of the electric generator.

The kinetic energy of flowing water or potential energy of water at a height can be converted into electricity. The hydropower plants are associated with dams. The water from the high level in the dam is carried through pipes, to the turbine and thus electricity is generated.

NCERT Solutions for Class 10 Science Chapter 14 Sources of Energy

In-text Questions (Page 253)

Question 1.
What kind of mirror concave, convex or plain-would Be best suited for use in a solar cooker ? Why?
Answer:
Plane mirror, because it is a good reflector and a temperature inside the cooker goes upto 100° to 140°c. This heat is sufficient to cook the food easily. If other mirrors are used, the temperature is very low or high. At low temp, food is not cooked well and at very high temperature food is damaged or looses its taste.

Question 2.
What are the limitations of the energy that can be obtained form the oceans ?
Answer:

  1. The energy potential from the oceans is quite large, but efficient commerical exploitation is difficult.
  2. The setting of a ocean power plant is very difficult.

Question 3.
What is geothermal energy ?
Answer:
The energy which is obtained due to geological changes is called geothermal energy.

Question 4.
What are the advantages of nuclear energy ?
Answer:

  • It does not create air pollution.
  • A small amount of fuel is able to produce a tremendous amount of energy.
  • The nuclear energy produced can be converted into electricity easily.
  • Once the nuclear fuel is loaded into a nuclear power plant, than it will go on releasing energy for two or three years.

In-text Questions (Page 253)

Question 1.
Can any source of energy be pollution fee ? Why or why not ?
Answer:
C. N. G is considered as a pollution free fuel because it does not produce any poisonous or polluting gas on burning and it also does not produce particulate matter on burning. Solar energy is also in the same category. A source of energy be considered polluted if it produce poisonous gaseous and particulates matter on burning eg. coal.

Question 2.
Hydrogen has been used as a rocket fuel. Would consider it a cleaner fuel than CNG? Why or why not ?
Answer:
Hydrogen has been used as a rocket fuel. The chemical reaction involved is :
H2(g) + O2 (g) H2O (l) + 286 kJ

It is considered a cleaner fuel than C. N. G, because its combustion product is water. So hydrogen as a fuel provides pollution free atmosphere.

NCERT Solutions for Class 10 Science Chapter 14 Sources of Energy

In-text Questions (Page 254)

Question 1.
Name Two energy sources that you would consider to be renewable. Give reasons for your choices.
Answer:
Renewable sources :

  1. Wind energy.
  2. Water energy Because if these sources are consumed continously, they will not get exhausted.

Question 2.
Give the name of two energy sources that you would consider to be exhaustible. Give reasons for your choice.
Answer:
Exhaustible energy sources :
(i) Coal, (ii) Petroleum.
Because if these sources are consumed, they will get exhausted.

Class 10 Science Chapter 14 Sources of Energy Textbook Questions and Answers

Page no. 254-255

Question 1.
A solar water heater cannot be used to get hot water on:
(a) a sunny day
(b) a cloudy day
(c) a hot day
(d) a windy day
Answer:
(b) A cloudy day.

Question 2.
Which of the following is not an example of a biomass energy source :
(a) wood
(b) gobar-gas
(c) atomic energy
(d) coal.
Answer:
(c) Atomic energy

Question 3.
Most of the sources of energy we use represent stored solar energy. Which of the following is not ultimately derived from the sun’s energy:
(a) geothermal energy
(b) wind energy
(c) fossil fuels
(d) bio-mass.
Answer:
(a) Geothermal energy.

NCERT Solutions for Class 10 Science Chapter 14 Sources of Energy

Question 4.
Compare and constrast fossil fuels and the sun as direct sources of energy.
Answer:
Fossils fuel :

  1. It is a non-renewable sources.
  2. Fossil fuel are formed in nature long ago under special conditions of temperature and pressure.
  3. It is exhaustable source of energy.
  4. Coal and petroleum are the main fossils fuel.
  5. It causes pollution.

Solar energy or sun as direct source of energy:

  1. It is a renewable source of energy energy.
  2. The sun is the ultimate source of all forms of energy available on earth.
  3. It is in exhaustible source of energy.
  4. Solar energy, wind energy Ocean energy and hydro energy are the main forms of sun energy.
  5. It does not causes pollution.

Question 5.
Compare and constrast bio-mass and hydroelectricity as sources of energy
Answer:
Bio-mass: Wood has been used as a fuel for a long time. If we can ensure that enough trees are planted, a continuous supply of fire-wood can be assured. We are also familiar with the use of cow-dung cakes as a fuel. Given the large live-stock population in India, this can also assure us a steady source of fuel. Since these fuels are plant and animal products, the source of these fuels is said to be bio-mass. These fuels, however do not produce much heat on burning and a hot of smoke is given out when they are burnt. So, technological inputs to improve the efficiency of these fuels are necessary. When wood is burnt in a limited supply of oxygen, charcoal is formed. Charcoal bums without flame, is comparatively smokeless and has a higher heat generation efficiency.

Similarly cow dung, various plant materials like the residue after harvesting the crops, vegetable waste and sewage are decomposed in the absence of oxygen to give biogas. Biogas is an excellent fuel as it contains up to 75% methane. It has high heat capacity, it burns without smoke.

Hydro-electricity: The flowing water has both kinetic as well as potential energy The energy of the flowing water is called hydro-energy. It is an important renewable source of energy. The hydro energy has been traditionally used in past for grinding of grains just by turning the water wheel. Presently, the hydro energy is used to generate electricity by turning the blades of a turbine. The electricity, thus generated by flowing water is called hydro electricity For generating hydro-electricity, a dam is constructed across a river to block the flow of water in the reservoir behind the dam. The huge turbine blades are turned by the water as it flows down from the dam. The hydro-electricity generated by flowing water is transmitted to far away from the power station for supply to factories and homes through conducting wires.

Question 6.
What are the limitations of extracting energy from: (a) the wind ? (b) waves ? (c) tides ?
Answer:
(a) Limitations of wind energy:

  • The appliances or machines operating with wind energy stop working as soon as wind stops.
  • The minimum speed of wind to operate generator to produce electricity is about 15 km/h. As soon as the speed of the wind becomes less than 15 km/h, the generator stops working.
  • The use of wind energy is limited to certain places where wind is in plenty and blows most of the time.
  • Wind energy is not sufficient to operate very heavy machines

(b) Limitations of waves energy:

  • Wave energy would be available proposition only where waves are very strong.
  • Strong winds blowing across the sea only can general wave.

(c) Limitations of tidal energy :
To operate tidal power plant, the difference between the water levels of high tide and low tide should be very large. This much level of tide is not available at all coastal places, Thus, tidal power plants cannot be installed everywhere.

Question 7.
On what basis would you classify energy sources as :
(a) renewable and non-renewable ?
(b) exhaustible and inexhaustible? Are the options given in (a) and (b) the same ?
Answer:
(a) Renewable and non-renewable sources : The sources of energy which keep on renewing themselves regularly are called renewable sources, e.g. solar energy, wind energy. The sources of energy that cannot be renewed quickly are known as non-renewable sources eg. coal, petroleum etc.

(b) Exhaustible and non-exhaustible : If the sources of energy consumed continously, they will get exhausted, is called exhaustible sources of energy e.g. coal, petroleum. If the source of energy are consumed continuously, they will not get exhausted is called non exhaustible sources of energy, e.g. water energy, wind energy, solar energy etc.

NCERT Solutions for Class 10 Science Chapter 14 Sources of Energy

Question 8.
What are the qualities of an ideal source of energy?
Answer:
Qualities of an ideal source of energy.

  • It should supply enough amount of useful energy.
  • It should be easily stored.
  • It should be easily transported.
  • It should supply useful energy in a controlled manner.
  • It should occupy less space for storage.
  • It should be easily available.
  • It should be cheap.
  • It should be pollution free.

Question 9.
What are the advantages and disadvantages of using a solar cooker ? Are there places where solar cookers would have limited utility ?
Answer:
Advantages of solar cooker:

  • Economical. The cost of cooking food in the solar cooker is very small as money is only spent to purchase the solar cooker.
  • It saves the costly fuel like wood, gas, kerosene etc.
  • It can cook two or three dishes at a time.
  • Nutrition value of food is preserved as the food is cooked at low temperature.
  • Pollution. No pollution is caused as there is no burning of fuel.

Disadvantages :

  • Food cannot be cooked at night.
  • Food cannot be cooked on a cloudy day.
  • Food cannot be cooked quickly as solar cookers takes 4 to 5 hours to cook it.
  • Large quantity of food cannot be cooked with the solar cooker.
  • Chapatti cannot be made with this cooker.
  • Food cannot be fried.
  • The position of the reflecting plane mirror has to be changed time and again so that it always faces the sun.

Solar cooker have limited utility in the hill area and the cloudy places.

Question 10.
What are the environmental consequences of increasing demand for energy? What steps would you suggest to reduce energy consumption.
Answer:
We have studied a large number of sources of energy. Exploiting any source of energy disturbs the environment in some way or the other. In any given situation, the source we would choose depends on factors such as the ease of extracting energy from that source, the economics of extracting energy from the source, the efficiency of the technology available and the environmental damage that will be caused by using that source. We have already seen that burning fossil fuels causes air pollution Research continues in these areas to produce longer lasting device that will cause less damage throughout their life.

We can contribute a lot to save energy by adopting the following strategies in our day-to-day activities.

  • We must switch off the lights, fans and other home appliances running by electricity when they are not required.
  • We should always use efficient appliances.
  • We should close the water taps immediately after using it.
  • We should always cover the vessels while cooking our food.
  • Solar cookers, solar water heaters and solar dryers should be preferred wherever possible.
  • Pulses, rice, etc., should be soaked in water for at least 1520 minutes before cooking.
  • We must use pressure cooker for cooking rice, dal, meat, vegetables etc.
  • We should prefer to use public transport for travelling as they consume less fuel energy per head as compared to the individual vehicles.

Class 10 Science Chapter 14 Sources of Energy Textbook Activities

Activity 14.1 (Page 242)

  • List four forms of energy that you use from morning, when you wake up, till you reach the school.
  • From where do we get these different forms of energy ?
  • Can we call these ‘sources’ of energy? Why or why not?

Observation : The muscular energy for carrying out physical work, electrical energy for running various appliances, chemical energy for cooking food or running a vehicle all come from some source. We need to know how do we select the source needed for obtaining the energy in its usable form.

NCERT Solutions for Class 10 Science Chapter 14 Sources of Energy

Activity 14.2 (Page 243)

  • Consider the various options we have when we choose a fuel for cooking our food.
  • What are the criteria you would consider when trying to categorise something as a good fuel?
  • Would your choice be different if you lived
    (a) in a forest?
    (b) in a remote mountain village or small island?
    (c) in New Delhi?
    (d) lived five centuries ago?
  • How are the factors different in each case?
    Criteria for a good fuel:
  • A good fuel would do a large amount of work per unit volume or mass.
  • be easily accessible.
  • be easy to store and transport and
  • perhaps most importantly be economial.
    (a) wood
    (b) cow dung cake or biomass fuel
    (c) L.P.G.
    (d) fats obtain from animals.
  • The availability of the fuel is tht main factor in each case.

Activity 14.3 (Page 244)

  • Take a table tennis ball and make three slits into it.
  • Put semicircular ( ) fins cut out of a metal sheet into these slits.
  • Pivot the tennis ball on an axle through its centre with a straight metal wire fixed to a rigid support. Ensure that the tennis ball rotates freely about the axle.
  • Now connect a cycle dynamo to this.
  • Connect a bulb in series.
  • Direct a jet of water or steam produced in a pressure cooker at the fins (Fig.). What do you observe?

NCERT Solutions for Class 10 Science Chapter 14 Sources of Energy 1

Observation :
This is our turbine for generating electricity. The simplest turbines have one moving part, a rotor-blade assembly. The moving fluid acts on the blades to spin them and impart energy to the rotor. Thus, we see that basically we need to move the fan, the rotor blade, with speed which would turn the shaft of the dynamo and convert the mechanical energy into electrical energy – the form of energy which has become a necessity in today’s scenario. The various ways in which this can be done depends upon availability of the resources.

NCERT Solutions for Class 10 Science Chapter 14 Sources of Energy

Activity 14.4 (Page 248)

Find out from your grand-parents or other elders –

Question 1.
How did they go to school?
Answer:
Our grand-parents or other eiders went to school on foot.

Question 2.
How did they get water for their daily needs when they were young?
Answer:
They got water from ponds and well for their daily needs when they were young.

Question 3.
What means of entertainment did they use?
Answer:
Games such as kabaddi, kho-kho etc. were the main source of entertainment.

Question 4.
Compare the above answers with how you do these tasks now.
Answer:
Now a days we go to school by bus. We get water through water pipelines or through tube-well. T.V.V.CR movies etc. are the means of entertainment.

Question 5.
Is there a difference? If yes, in which case more energy from external sources is consumed?
Answer:
Yes there is a difference. Now a days (modern age) more energy is consumed from external sources.

Activity 14.5 (Page 249)

  • Take two conical flasks and paint one white and the other black. Fill both with water.
  • Place the conical flasks in direct sunlight for half an hour to one hour.
  • Touch the conical flasks. Which one is hotter? You could also measure the temperature of the water in the two conical flasks with a thermometer.
  • Can you think of ways in which this finding could be used in your daily life?

A black surface absorbs more heat as compared to a white or a reflecting surface under identical conditions. Solar cookers and solar water heaters use this property in their working. Some solar cookers achieve a higher temperature by using mirrors to focus the rays of the Sun. Solar cookers are covered with a glass plate.

NCERT Solutions for Class 10 Science Chapter 14 Sources of Energy

Activity 14.6 (Page 249)

  • Study the structure and working of a solar cooker and/or a solar water-heater, particularly with regard to how it is insulated and maximum heat absorption is ensured.
  • Design and build a solar cooker or water- heater using low-cost material available and check what temperatures are achieved in your system.

Question 1.
Discuss what would be the advantages and limitations of using the solar cooker or water-heater.
Answer:
It is easy to see that these devices are useful only at certain times during the day. This limitation of using solar energy is overcome by using solar cells that convert solar energy into electricity. A typical cell develops a voltage of 0.5-1 V and can produce about 0.7 W of electricity when exposed to the Sun A large number of solar cells are, combined in an arrangement called solar cell panel (Fig.) that can deliver enough electricity for practical use.
NCERT Solutions for Class 10 Science Chapter 14 Sources of Energy 2
NCERT Solutions for Class 10 Science Chapter 14 Sources of Energy 3

The principal advantages associated with solar cells are that they have no moving parts, require little maintenance and work quite satisfactorily without the use of any focusing device. Another advantage is that they can be set up in remote and inaccessible hamlets or very sparsely inhabited areas in which laying of a power transmission line may be expensive and not commercially viable.

Activity 14.7 (Page 252)

Question 1.
Discuss in class the question of what is the ultimate source of energy for bio-mass, wind and ocean thermal energy.
Answer:
Sun is the ultimate source of energy for bio-mass, wind and ocean thermal energy.

Question 2.
Is geothermal energy and nuclear energy different in this respect? Why?
Answer:
Geothermal energy and nuclear energy is different because geothermal energy is produced due to geological changes and nuclear energy is produced by splitting of heavier nuclei into smaller or combination of lighter nuclei into heavier.

Question 3.
Where would you place hydroelectricity and wave energy?
Answer:
They are in the category of wind energy and biomass energy.

NCERT Solutions for Class 10 Science Chapter 14 Sources of Energy

Activity 14.8 (Page 253)

  • Gather information about various energy sources and how each one affects the environment.
  • Debate the merits and demerits of each source and select the best source of energy on this basis.

We have studied various sources of energy like coal, petroleum, CNG, LPG, wind energy, ocean energy etc. Exploiting any source of energy disturbs the environment in some way or the other. In any given situation, the source we would choose depends on factors such as the ease of extracting energy from that source, the economics of extracting energy from the source, the efficiency of the technology available and the environmental damage that will be caused by using that source. But the fuels like CNG is said to be clean fuel, it would be more exact to say that a particular source is cleaner than the other. We have already seen that burning fossil fuels causes air pollution. In some cases, the actual operation of a device like the solar cell may be pollution free, but the assembly of the device would have caused some environmental damage. Research continues in these areas to produce longer lasting devices that will cause less damage throughout their life. C. N. G. and solar cell is the best source of energy.

Activity 14.9 (Page 254)

Question 1.
Debate the following two issues in class.
(a) The estimated coal reserves are said to be enough to last us for another two hundred years. Do you think we need to worry about coal getting depleted in this case? Why or why not?
(b) It is estimated that the Sun will last for another five billion years. Do we have to worry about solar energy getting exhausted? Why or why not?
Answer:
(a) The growing demand for energy is largely met by the fossil fuels like coal. Our technologies were also developed for using these energy sources. But coal was formed over millions of years ago and there are only limited reserves. The fossil fuels are non-renewal source of energy, so we need to conserve them. If we were to antique consuming these source at such alarming rates, we would soon run out of energy. In order to avoid this, alternate source of energy were explored. So we need to worry about coal getting depleted. But actually a large number of alternative source of energy also exist like wind energy, ocean energy etc. there is no need to worry about coal getting depleted.

(b) Sun is the ultimate source of energy on earth. Animals and plants can survive only in presence of sunlight. If solar energy gets exhausted then all the living things will also die. So we have to worry about solar energy getting exhausted.

But actually renewable energy is available in our natural environment, in the form of some continuing or repetitive currents of energy, or is stored in such large underground reservoirs that rate of depletion of the reservoir because of extraction of usable energy is practically negligible. So no need to worry about solar energy getting exhausted.

Question 2.
On the basis of the debate, decide which energy sources can be considered
(i) exhaustible,
(ii) inexhaustible,
(iii) renewable and
(iv) non-renewable.
Give your reasons for each choice.
Answer:
(i) Exhaustible : Coal, petroleum
(ii) Inexhaustible : Wind energy, ocean energy
(iii) Renewable : Wind energy, solar energy.
(iv) Non-renewable : Coal, petroleum.

Class 10 Science Chapter 14 Sources of Energy Additional Important Questions and Answers

Very Short Answer Type Questions

Question 1.
Give two forms of energy which is mainly utilised at our house ?
Answer:
Heat and electricity.

Question 2.
Name any two renewable sources of energy ?
Answer:
Wind energy, ocean energy.

NCERT Solutions for Class 10 Science Chapter 14 Sources of Energy

Question 3.
Name the radiation of sunlight that mainly carries heat with it.
Answer:
Infrared radiation.

Question 4.
Name any two radiations of solar energy that are not visible to us.
Answer:

  1. Ultraviolet,
  2. Intra-red.

Question 5.
Name the type of radiation emitted by a hot electric iron.
Answer:
Intra-red radiation

Short Answer Type Questions

Question 1.
Mention any four areas where solar cells are being used a source of energy.
Answer:

  1. In operating radio and TV sets in remote/rural areas.
  2. In calculators and in wrist watches.
  3. In light houses and offshore drilling operations.
  4. In research centres located in remote areas.

Question 2.
Why wind energy farms on be established only at specific locations ? Give reasons to support your answer.
Answer:
Wind energy farms should be built at specific locations because :

  • Wind should blow for greater part of the year.
  • Wind should be steady.
  • Wind should be strong blowing atleast the speed of 15 km/hr.
  • Moreover, the establishment of wind energy farms require large areas of land besides a high cost of construction.

Question 3.
It is difficult to use hydrogen as a source of energy, although its calorific value is quite high. Explain.
Answer:
It is difficult to use hydrogen as a source of energy although its calorific value is quite high due to following reasons :

  • It is explosive in nature because it catches fire easily with oxygen.
  • It is an expensive fuel because a lot of money is required for its production.
  • Its storage and transportation is not very easy.

NCERT Solutions for Class 10 Science Chapter 14 Sources of Energy

Long Answer Type Question

Question 1.
All heat produced by the burning of cow dung cake of mass 20 gm was used to heat water of 50 gm. If the temperature of water is raised to 2°C, calculate the calorific value of the cow dung cake. Assume specific heat capacity of water = 4.2 J/g°C,
Answer:
Mass of cow dung cake, m = 200 m
Mass of water m = 50 gm
Specific heat capacity of water, C = 4.2 J/gm°C
Rise of temperature of water, ΔQ = 2°C
Heat absorbed by water = Q
= m, CΔQ = 50gm × 4.2J/gm 2°C × 420 J.
This heat absorbed = Heat produced by burning of cow dung cake.
Caloric value of cow dung = \(\frac{\mathrm{Q}}{\mathrm{m}}=\frac{420 \mathrm{~J}}{200 \mathrm{gm}}\) = 2.1 Jgm-1

Multiple Choice Questions

Question 1.
A renewable source of energy :
(a) LPG
(b) Coal
(c) Petroleum
(d) Wind energy
Answer:
(d) Wind energy

Question 2.
Non-renewable source of energy :
(a) Natural gas
(b) Ocean energy
(c) Geothermal energy
(d) Wind energy
Answer:
(a) Natural gas

Question 3.
Solar cooker is based on :
(a) Solar energy
(b) Wind energy
(c) Hydro energy
(d) Chemical energy
Answer:
(a) Solar energy

Question 4.
Solar cooker is not used for the following purpose :
(d) Preparation of rice
(b) Preparation of pulses
(c) Preparation of grams
(d) Frying of foods.
Answer:
(d) Frying of foods.

Question 5.
The estimated energy of sun reaches per second per square meter is :
(a) 1.4 kJ
(b) 1.5 kJ
(c) 1.6 kJ
(d) 1.3 kJ
Answer:
(a) 1.4 kJ

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