OR<\/strong><\/p>\nSoaps and detergents are both types of salts. State the difference between the two. Write the mechanism of the cleansing action of soaps. Why do soaps not form lather (foam) with hard water? Mention any two problems that arise due to the use of detergents instead of soaps.<\/p>\n
Question 18.<\/strong>
\nHow we should lead our life in the present day to be more environment friendly ?\u00a0\u00a0[5]<\/strong><\/p>\nQuestion 19.<\/strong>
\n(a) Define optical centre of a spherical lens.\u00a0\u00a0[5]<\/strong>
\n(b) A divergent lens has a focal length of 20 cm. At what distance should an object of height 4 cm from the optical centre of the lens be placed so that its image is formed 10 cm away from the lens ?
\n(c) Show the ray diagram for the above.<\/p>\nQuestion 20.<\/strong>
\nHow did the Modem Periodic Table remove the anomalies of Mendeleev’s Periodic Table ?\u00a0\u00a0[5]<\/strong><\/p>\nQuestion 21.<\/strong>
\nThe touch-me-not plant folds its leaves in response to touch. How does this reaction happen in the plant ?\u00a0\u00a0[5]<\/strong><\/p>\nOR<\/strong><\/p>\nWhat are reflex actions ? Give examples ? Explain reflex arc by an example with labelled diagram.<\/p>\n
SECTION-B<\/strong><\/p>\nQuestion 22.<\/strong>
\n(a) An atom has an electronic configuration of 2,8,7. What is the atomic number of this element ?\u00a0\u00a0[2]<\/strong>
\n(b) Can you find out the element with atomic number 17 ? What kind of bond will it form on combination with other atoms ?<\/p>\nQuestion 23.<\/strong>
\nWhat is a thermite reaction and where is it used ?\u00a0\u00a0[2]<\/strong><\/p>\nQuestion 24.<\/strong>
\nWhy and how is the brain protected ?\u00a0\u00a0[2]<\/strong><\/p>\nQuestion 25.<\/strong>
\nWhen you cut open a hibiscus flower what are the major parts you see ? Draw and label them.\u00a0\u00a0[2]<\/strong><\/p>\nQuestion 26.<\/strong>
\nIn an experiment to study the dependence of potential difference (V) on the electric current (I) across a conductor (resistor), if the circuit is on for a long time, then select two correct options from the ones given below:\u00a0\u00a0[2]<\/strong><\/p>\n\n- Zero error of the ammeter will be changed.<\/li>\n
- Zero error of the voltmeter will be changed.<\/li>\n
- Value of resistance will be changed.<\/li>\n
- Resistor will be heated.<\/li>\n<\/ol>\n
OR<\/strong><\/p>\nDraw a circuit to study the dependence of current on the potential difference across a resistor.<\/p>\n
Question 27.<\/strong>
\nAn object of height 2.5 cm is placed at a distance of 15 cm from the optical centre ‘O’ of a convex lens of focal length 10 cm. Draw a ray diagram to find the position of the image formed. Mark the optical centre, ‘O’, principal focus ‘F’ and height of the image on the diagram.\u00a0\u00a0[2]<\/strong><\/p>\nANSWERS<\/strong><\/span>
\nSECTION-A<\/strong><\/p>\nAnswer 1.<\/strong>
\nTrypsin is an enzyme found in the pancreatic juice which helps to digest proteins whereas Pepsin is an enzyme found in the stomach and it helps to digest proteins too.<\/p>\nAnsswer 2.<\/strong>
\nRegeneration is the ability of organisms to give rise to new individual organisms from their body parts. If an individual is cut or broken up into many pieces, these pieces can grow into separate individuals. This is seen in simple animals like Hydra and Planaria.<\/p>\nAnsswer 3.<\/strong>
\nGalvanisation is the process of applying a protective zinc coating to iron or steel, to prevent rusting.<\/p>\nAnsswer 4.<\/strong>
\nGiven: u = -15 cm, \u0192= 20 cm<\/p>\nAccording to formula,<\/p>\n
\\(\\frac { 1 }{ f } =\\frac { 1 }{ \\upsilon } -\\frac { 1 }{ u } \\)
\n\\(\\frac { 1 }{ 20 } =\\frac { 1 }{ \\upsilon } +\\frac { 1 }{ 15 } \\)
\n\\(\\frac { 1 }{ 20 } -\\frac { 1 }{ 15 } =\\frac { 1 }{ \\upsilon } \\)
\n\\(-\\frac { 1 }{ 60 } =\\frac { 1 }{ \\upsilon } \\)
\n\\(\\upsilon =-60cm\\)<\/p>\n
The four characteristics of the image formed by the lens are:<\/p>\n
\n- It is a virtual image.<\/li>\n
- It is an erect image.<\/li>\n
- It is an enlarged image.<\/li>\n
- It is at a distance of 60 cm on the same side of the lens as the object.<\/li>\n<\/ul>\n
Ansswer 5.<\/strong>
\nHuman beings have 23 pairs of chromosomes. One chromosome of each pair is maternal and one is paternal. Of the 23 pairs, 22 pairs are called perfect pairs. One pair called the sex chromosomes are different. In women there are two X chromosomes while in men there is one X and one Y chromosome. So women are XX and men are XY.<\/p>\nAnsswer 6.<\/strong>
\nThe given equation tells us the relationship between potential difference, charge, and work done to move the charge. The equation shows that the electric potential difference between two points in , an electric circuit carrying some current is the work done to move a unit charge from one point to another. The unit of V is named after Alessandro Volta, an Italian physicist. The S.I. unit of potential difference is volt.<\/p>\nOR<\/strong><\/p>\nGiven: V = 16 volt, I = 4.0 ampere, t = 6 hours<\/p>\n
\n- Resistance, R = V\/I = \\(\\frac { 16 }{ 4 } \\) = 4\u2126<\/li>\n
- Power,P = V x I = 16 x 4 = 64W<\/li>\n
- Electrical energy, W = VIt = 16 x 4 x 6 = 384 Wh = 0.384 kWh<\/li>\n<\/ul>\n
Ansswer 7.<\/strong>
\nThese resistors should be connected in parallel with the battery to get maximum current.
\n![\"CBSE](\"https:\/\/i2.wp.com\/www.ncert-solutions.com\/wp-content\/uploads\/2018\/10\/CBSE-Sample-Papers-for-Class-10-Science-Set-4-1.png?resize=204%2C150&ssl=1\")
\nLet the equivalent resistance be R \u2126.<\/p>\n\\(\\frac { 1 }{ R } =\\frac { 1 }{ r } +\\frac { 1 }{ r } +\\frac { 1 }{ r } \\)
\n\\(\\frac { 1 }{ R } =\\frac { 1+1+1 }{ r } =\\frac { 3 }{ r }\\)
\n\\(R=\\frac { r }{ 3 } \\)
\nV=I \u00d7 R<\/p>\n
According to ohm’s law,<\/p>\n
Current(I) = E \u00d7 \\(\\frac { 3 }{ r } =\\frac { 3E }{ r } \\)<\/p>\n
Answer 8.<\/strong>
\nThe process by which carbon exists in different forms is called allotropy. The different compounds have the same chemical properties but very different physical properties. Diamond and graphite are the two allotropic forms of carbon. There is a difference in the properties because of a difference in which the carbon atoms are bonded to one another. In diamond, each carbon atom is bonded to four other carbon atoms forming a rigid three-dimensional structure. In graphite, each carbon atom is bonded to three other carbon atoms in the same plane giving a hexagonal array. One of these is a double bond and thus the valency of carbon is satisfied.
\n![\"CBSE](\"https:\/\/i1.wp.com\/www.ncert-solutions.com\/wp-content\/uploads\/2018\/10\/CBSE-Sample-Papers-for-Class-10-Science-Set-4-2.png?resize=547%2C212&ssl=1\")
<\/p>\nAnswer 9.<\/strong>
\nWater of crystallisation is the fixed number of water molecules present in one formula unit of a salt. When we heat the crystals, this water is removed and the salt turns white. 1 formula unit of CuSO4<\/sub> has 5 water molecules so it is written as CuSO4<\/sub>.5H2<\/sub>O. Gypsum is another salt which has water of crystallisation. It has 2 water molecules. It has the formula CaSO4<\/sub>.2H2<\/sub>O. The crystalline solids which do not contain water of crystallisation are NaCl, KNO3<\/sub>, C12<\/sub>H22<\/sub>O11<\/sub> and KMnO4<\/sub>.<\/p>\nAnswer 10.<\/strong>
\nDams are built to generate hydroelectric power. Water is stored in huge dams built at great heights. Since the water in the reservoir would be refilled every time it rains hydroelectric power is a renew-able source of energy. However, there are some problems associated with the construction of dams. Large areas of agricultural land and human habitation has to be sacrificed. Large ecosystems could be destroyed while submerged and rotting vegetation could give rise to greenhouse gases. Suitable and satisfactory rehabilitation of the displaced people has to be ensured. Medha Phatkar is a famous social activist and she was associated with the “Narmada Bachao Andolan<\/strong>” against the construction of the Sardar Sarovar project on river Narmada.<\/p>\nOR<\/strong><\/p>\nAs an individual we can follow the principle of reduce, recycle and reuse (3Rs strategy)<\/strong> to reduce our consumption of the various natural resources.<\/p>\n\n- Reduce: We can reduce our consumption of various resources like electricity consumption by switching off unnecessary lights and fans.We can save water by immediately repairing faulty taps and should ensure there is no unnecessary wastage of water. We should not waste food and can prepare only as much as required.<\/li>\n
- Recycle : We must clearly segregate recyclable wastes like plastic, paper, metal and glass and use them to make something fresh instead of preparing something new.<\/li>\n
- Reuse: In this process, we need to find alternative uses for the things that we once considered waste. Used bottles or containers can be used to store various things at home. One side papers can be used for writing on the other side as a scribbling pad. Recycling of used things greatly reduces waste generation.
\nFinally we must manage our natural resources in such a way that they shall last for the future generations and are not exploited for short time gains.<\/li>\n<\/ol>\nAnswer 11.<\/strong>
\nA decrease in the amount of haemoglobin in our body means anaemia and a general weakness of the body. Haemoglobin is the oxygen carrying pigment of the blood. In its absence very little oxygen would be transported which means all the cells will not receive their supply of oxygen. In the absence of oxygen, food will not be oxidised and there will be no release of energy. This in turn affects the body’s ability to do work.<\/p>\nAnswer 12.<\/strong>
\nThe ability of the eye lens to adjust its focal length is called power of accommodation of the human eye.
\nThe focal length of the human eye lens can change i.e., increase or decrease depending on the distance of the object from the eye and because of this the image distance does not change. As the distance of the object from the eye varies, the ciliary muscles modify the curvature of the lens to change its focal length.
\n![\"CBSE](\"https:\/\/i0.wp.com\/www.ncert-solutions.com\/wp-content\/uploads\/2018\/10\/CBSE-Sample-Papers-for-Class-10-Science-Set-4-3.png?resize=606%2C160&ssl=1\")
<\/p>\nAnswer 13.<\/strong>
\npH is important in our daily lives. It plays a role in our digestive system, self-defence of animals and
\nplants and in tooth decay.<\/p>\n\n- Digestive system: Our stomach produces hydrochloric acid to help in digestion of food. Some\u00actimes during indigestion or when a person is hungry for long too much of acid is produced and this causes pain and irritation. To neutralise this, the patient is given antacids which contains a mild base.<\/li>\n
- Self-defence of animals and plants : Sometimes when we are stung by a honey-bee or ants it causes pain, swelling and irritation. This is due to an acid produced at the site of the sting. For relief, baking soda is used as it contains a mild base.<\/li>\n
- Tooth decay: Tooth decay is caused by bacteria which produce acids using the left-over food in our mouth. This can be avoided by cleaning the mouth regularly after eating. Toothpastes are slightly basic and they neutralise the excess acid in the mouth and prevent tooth decay.<\/li>\n<\/ol>\n
OR<\/strong><\/p>\nGypsum is a salt which has water of crystallisation. It has 2 water molecules as water of crystallisation. When it is heated it loses the water molecules and becomes calcium sulphate hemihydrate (CaSO4<\/sub>.1\/2H2<\/sub>O) this is called Plaster of Paris. It is a white powder and when mixed with water it changes again to gypsum which is a hard solid mass.
\n![\"CBSE](\"https:\/\/i2.wp.com\/www.ncert-solutions.com\/wp-content\/uploads\/2018\/10\/CBSE-Sample-Papers-for-Class-10-Science-Set-4-4.png?resize=349%2C58&ssl=1\")
<\/strong><\/p>\nUses of Plaster of Paris:<\/strong><\/p>\n\n- It is used as plaster for supporting fractured bones in the right position.<\/li>\n
- It is used for making toys, materials for decoration and for making smooth surfaces.<\/li>\n<\/ul>\n
Answer 14.<\/strong>
\nMendel performed his experiments using contrasting characters of pea plants. He crossed a tall plant (TT) and a dwarf plant (tt). In the F1<\/sub> generation he found all plants to be tall. Now Mendel wanted to see if all the tall plants of F1 generation were like the tall parents. So he self-pollinated the F1\u00a0tall plants. In F2, he found 3\/4th<\/sup> plants were tall and rest l\/4th<\/sup> were dwarf. This clearly shows that though both the tall and dwarf characters were inherited in F1, only tallness trait expressed itself. This means both TT and Tt are tall plants while tt is a dwarf plant. Hence, a single copy of T is enough to express tallness while 2 copies of t are required to express dwarfness. Moreover Tt did not express any in between character. Thus Mendel’s experiments clearly show that traits could either be dominant or recessive.
\n![\"CBSE](\"https:\/\/i2.wp.com\/www.ncert-solutions.com\/wp-content\/uploads\/2018\/10\/CBSE-Sample-Papers-for-Class-10-Science-Set-4-5.png?resize=422%2C405&ssl=1\")
<\/p>\nAnswer 15.<\/strong><\/p>\n\n\n\nArteries<\/strong><\/td>\nVeins<\/strong><\/td>\n<\/tr>\n\n(i)\u00a0<\/strong> Arteries have thick, elastic walls<\/td>\n| Veins have thin walls.<\/td>\n<\/tr>\n | \n(ii)<\/strong> Arteries carry blood from the heart to different parts of the body<\/td>\n| Veins collect blood from different and bring it to the heart<\/td>\n<\/tr>\n | \n(iii)<\/strong> Arteries carry pure or oxygenated blood.<\/td>\n| Veins carry impure or deoxygenated blood.<\/td>\n<\/tr>\n | \n(iv)<\/strong> Blood flows at high pressure in the arteries.<\/td>\n| Blood flows at lower pressure in the veins.<\/td>\n<\/tr>\n | \n(v)<\/strong> Arteries are placed deep inside muscles.<\/td>\n| Veins are placed superficially.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n Answer 16.<\/strong>
\nThe electric fuse plays an important role in the domestic circuit. It is a safety device which is used to limit the current in an electric circuit. The use of a fuse safeguards the circuit and the appliances connected in that circuit from being damaged. The fuse is always connected in series with the device. A fuse is a short piece of wire of uniform area of cross-section and high resistance, made up of a material of low melting point, so that it may easily melt due to overheating when current in excess to the prescribed limit passes through it. Generally an alloy of lead and tin is used as the material of the fuse wire because its melting point is low and resistivity is more than that of copper, aluminium, etc.<\/p>\nThe main fuse in domestic wiring is encased in a cartridge of porcelain of similar material with metal ends. The fuses for domestic purposes are rated as 1 A, 2 A, 3 A, 5 A, 10 A etc.<\/p>\n Answer 17.<\/strong>
\nCarbon compounds are poor conductors of electricity. Carbon has a valency of 4. To attain the stable configuration of noble gases, carbon atom needs to either gain or lose 4 electrons.<\/p>\n\n- If it were to gain 4 electrons it would become C4-<\/sup> anion, but this makes it difficult to hold onto the 10 electrons.<\/li>\n
- If it were to lose 4 electrons it would become C4+\u00a0<\/sup>cation, but this means a lot of energy would be required to pull out the 4 electrons and leave the carbon atom with 6 protons and 2 electrons. The easy way out is to share the 4 electrons with atoms of either carbon or other elements. The shared pair is then common to both the atoms. This bond formed by a sharing of electrons is called as covalent bond and such compounds are known as covalent compounds. As there are no charged particles available covalent compounds are poor conductors of electricity. They have low melting and boiling points too.<\/li>\n<\/ol>\n
OR<\/strong><\/p>\n\n\n\nSoap<\/strong><\/td>\nDetergents<\/strong><\/td>\n<\/tr>\n\n(i)<\/strong> Soaps are sodium salts of long chain carbo-benzene sulphonic acids.<\/td>\n| Detergents are sodium salt of long chain xylic \u00a0acids.<\/td>\n<\/tr>\n | \n(ii)<\/strong> The ionic group in soap is COONa+<\/sup>.<\/td>\n| The ionic groups in detergents is S03<\/sub> , Na+<\/sup>.<\/td>\n<\/tr>\n | | | | | | | | | | | | |