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CBSE Class 10 Science 2026 — Paper 31(B)/SB

80 marks · 3 hours · 39 questions (45 with the OR choices)

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Questions 1–9 · 1 mark each

  1. Q1 1 mark
    The inner lining of the small intestine has numerous finger-like projections called villi. Choose the correct option indicating the function of villi.
    1. (a)It increases surface area for digestion of food.
    2. (b)It decreases surface area for absorption of food.
    3. (c)It secretes enzymes required for digestion of food.
    4. (d)It increases surface area for absorption of food.
    Show answer
    (d) It increases surface area for absorption of food.
    Step-by-step solution →
  2. Q2 1 mark
    Name the plant hormone that inhibits plant growth and is responsible for wilting of leaves.
    1. (a)Cytokinin
    2. (b)Abscisic acid
    3. (c)Auxin
    4. (d)Gibberellin
    Show answer
    (b) Abscisic acid
    Step-by-step solution →
  3. Q3 1 mark
    In a cross carried out by Mendel, when he crossed tall pea plant (TT) with a short pea plant (tt) in progeny (first generation), all the plants were found to be tall. Select the correct reason from the given options.
    1. (a)Tallness is the recessive trait
    2. (b)Shortness is the dominant trait
    3. (c)Tallness is the dominant trait
    4. (d)Height of pea plant is not governed by traits like tallness ‘T’ or shortness ‘t’
    Show answer
    (c) Tallness is the dominant trait
    Step-by-step solution →
  4. Q4 1 mark
    This freshwater organism is known for its amazing ability to reproduce by any of the two methods – either regeneration or budding. Identify the organism.
    1. (a)Amoeba
    2. (b)Hydra
    3. (c)Plasmodium
    4. (d)Planaria
    Show answer
    (b) Hydra
    Step-by-step solution →
  5. Q5 1 mark
    In which of the following structures of a cell does the process of breakdown of pyruvate using oxygen to form carbon dioxide, water and energy take place ?
    1. (a)Nucleus
    2. (b)Mitochondria
    3. (c)Cytoplasm
    4. (d)Chloroplast
    Show answer
    (b) Mitochondria
    Step-by-step solution →
  6. Q6 1 mark
    In a food chain, where plants are eaten by insects, insects are eaten by frog and frog is eaten by snake, if the energy available to the frog is J, then the energy available to the insects and snake respectively will be :
    1. (a) J and J
    2. (b) J and J
    3. (c) J and J
    4. (d) J and J
    Show answer
    (a) J and J
    Step-by-step solution →
  7. Q7 1 mark
    Consider the following statements about ozone and choose the correct option :
    1. (i)One molecule of ozone gas is formed by three atoms of oxygen.
    2. (ii)Ozone is the product of UV radiations acting on oxygen () molecules.
    3. (iii)Ozone performs an essential function at the lower levels of the atmosphere.
    4. (iv)Ozone is very useful and is essential for all aerobic forms of life. Options :
    1. (a)(i) and (iii)
    2. (b)(i) and (ii)
    3. (c)(ii) and (iv)
    4. (d)(iii) and (iv)
    Show answer
    (b) (i) and (ii)
    Step-by-step solution →
  8. Q8 1 mark
    For Questions number 8 and 9, two statements are given — one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.

    Assertion (A): Trachea does not collapse, even when there is no air in it.

    Reason (R): Trachea is supported by C-shaped ligament.

    1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
    2. (b)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
    3. (c)Assertion (A) is true, but Reason (R) is false.
    4. (d)Assertion (A) is false, but Reason (R) is true.
    Show answer
    (c) Assertion (A) is true, but Reason (R) is false.
    Step-by-step solution →
  9. Q9 1 mark
    For Questions number 8 and 9, two statements are given — one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.

    Assertion (A): Biological magnification leads to the accumulation of maximum concentration of harmful chemicals in human beings.

    Reason (R): Human beings occupy the top level in any food chain.

    1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
    2. (b)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
    3. (c)Assertion (A) is true, but Reason (R) is false.
    4. (d)Assertion (A) is false, but Reason (R) is true.
    Show answer
    (a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
    Step-by-step solution →

Questions 10–12 · 2 marks each

  1. Q10 2 marks
    Give any two ways in which non-biodegradable substances would effect the environment adversely.
    Show answer

    They persist because decomposers cannot break them down, and they pollute soil, water and air.

    (1) Non-biodegradable substances are not broken down by decomposers, so they persist in the environment for a long time and damage it: plastic and polythene waste, for example, litters the land, chokes drains and harms animals that swallow it. (2) They cause soil, air and water pollution: they pollute the soil and the water bodies where they are dumped or washed, and burning them releases harmful gases into the air.
    Step-by-step solution →
  2. Q11 2 marks
    Name the hormone which is responsible for the bending of plants towards light and also explain the process of bending of plants.
    Show answer

    Auxin, made at the shoot tip, moves to the shaded side and makes those cells grow longer, so the shoot bends towards light.

    The hormone is auxin, which is synthesised at the tip of the shoot. When light falls on the shoot from one side, auxin diffuses towards the shady side of the shoot. This higher concentration of auxin stimulates the cells on the shaded side to grow longer than the cells on the side facing the light, so the shaded side grows faster and the shoot bends towards the light. This growth response to light is called phototropism.
    Step-by-step solution →
  3. Q12 2 marks
    Mendel used a number of easily observable contrasting characters of garden pea plant. List any two pairs of such characters. Also mention the dominant and recessive character in each pair.
    Show answer

    Tall (dominant) and dwarf (recessive) stem height; round (dominant) and wrinkled (recessive) seed shape.

    Any two of Mendel's seven pairs, for example: (1) Height of the stem: tall is dominant and dwarf (short) is recessive. (2) Shape of the seed: round is dominant and wrinkled is recessive. Other correct pairs: colour of the seed (yellow dominant, green recessive); colour of the flower (violet dominant, white recessive); position of the flower (axial dominant, terminal recessive); shape of the pod (inflated dominant, constricted recessive); colour of the pod (green dominant, yellow recessive).
    Step-by-step solution →

Questions 13–14 · 3 marks each

  1. Q13 3 marks
    1. (a)How is the process of pollination different from fertilization ?
    2. (b)Where is the zygote located in the flower after fertilization ?
    Show answer

    Pollination is pollen transfer to the stigma; fertilization is fusion of germ-cells in the ovule; the zygote lies in the ovule within the ovary.

    (a) Pollination is the transfer of pollen grains from the anther of a stamen to the stigma of a carpel, by agents such as wind, water or insects. Fertilization is the fusion of the male germ-cell, carried down the pollen tube, with the female germ-cell (egg) inside the ovule, forming a zygote. So pollination is a transfer of pollen that ends on the stigma and comes first, while fertilization is a fusion of germ-cells that takes place inside the ovule in the ovary, comes after pollination and produces the zygote. (b) After fertilization the zygote is located inside the ovule, within the ovary of the flower. It develops into the embryo, the ovule becomes the seed and the ovary becomes the fruit.
    Step-by-step solution →
  2. Q14(a) 3 marks
    In human beings, digestion in the stomach is taken care of by the gastric glands present in the walls of the stomach. Briefly describe the function of gastric glands.
    Show answer

    Gastric glands secrete hydrochloric acid, pepsin and mucus: the acid helps pepsin digest proteins and kills germs, and mucus protects the lining.

    The gastric glands in the wall of the stomach release gastric juice, which contains: (1) Hydrochloric acid, which makes the medium in the stomach acidic so that the enzyme pepsin can act; it also kills germs that enter with the food. (2) Pepsin, a protein-digesting enzyme, which begins the digestion of proteins, breaking them into smaller peptides. (3) Mucus, which protects the inner lining of the stomach from the action of the acid under normal conditions.
    Step-by-step solution →
    OR
    Q14(b) 3 marks
    Briefly describe the role of saliva and pancreas in the digestion of food. Also, explain the peristaltic movement in the gut.
    Show answer

    Saliva's amylase digests starch; the pancreas adds trypsin, lipase and amylase; peristalsis is a muscle wave that pushes food along the gut.

    Saliva: secreted by the salivary glands into the mouth, it moistens the food so that it can be chewed and swallowed easily, and its enzyme salivary amylase breaks down starch into simple sugar (maltose). Pancreas: it secretes pancreatic juice into the small intestine; the juice contains trypsin, which digests proteins, lipase, which breaks down emulsified fats into fatty acids and glycerol, and amylase, which digests the remaining starch. Peristaltic movement: the muscles in the wall of the gut contract and relax rhythmically in a wave that travels along the tube; the muscle behind the food contracts while the muscle ahead of it relaxes, so the food is pushed forward. These movements occur all along the gut and carry the food from the mouth towards the anus.
    Step-by-step solution →

Question 15 · 4 marks

  1. Q15 4 marks
    Read the following passage and answer the questions that follow : Metabolic activities produce metabolic waste, which refers to by-products from the body’s energy-producing processes that are unusable and potentially toxic. These wastes need removal from the body to maintain health. The wastes like urea, water, salts, ammonia, etc. are excreted via kidneys, sweat or urine. is eliminated through the lungs.
    1. (i)What is the purpose of making urine in the human body ?[1]
    2. (ii)Name two main toxic wastes that kidneys filter from the blood.[1]
    3. (iii)(a)A major amount of water is selectively reabsorbed by the tubular part of the nephron. On what factors does the amount of water reabsorbed depend ?[2]
    4. (iii)(b)OR : Quantity of, or the frequency of passing urine is less in summer. Why ?[2]
    Show answer

    Urine removes wastes such as urea and uric acid; water reabsorption depends on body water and dissolved waste; summer sweating reduces urine.

    (i) Urine is made to filter the waste products, mainly nitrogenous wastes such as urea and uric acid, out of the blood and remove them from the body; this also removes excess water and salts, keeping their amounts in the body steady. (ii) Urea and uric acid. (iii)(a) The amount of water reabsorbed depends on (1) how much excess water there is in the body, and (2) how much dissolved waste there is to be excreted. OR (iii)(b) In summer a large amount of water is lost from the body as sweat, so there is less excess water in the body. The tubules of the nephrons therefore reabsorb more water, and the urine formed is less in quantity and more concentrated, so it is passed less often.
    Step-by-step solution →

Question 16 · 5 marks

  1. Q16(a) 5 marks
    Name the most suitable method of raising a banana plant. Is this mode of reproduction sexual or asexual ? List any three advantages of growing plants by such a method.
    Show answer

    A banana is raised by asexual vegetative propagation; advantages are earlier flowering and fruiting, propagation of seedless plants and offspring like the parent.

    Method: vegetative propagation. A banana plant is raised from a sucker - a young shoot that grows from the underground stem of an existing plant - because the cultivated banana has lost the capacity to produce seeds. Mode: asexual, because only one parent is involved and no gametes fuse. Three advantages: (1) plants raised this way bear flowers and fruits earlier than those grown from seeds; (2) plants that have lost the capacity to produce seeds, such as banana, orange, rose and jasmine, can still be propagated; (3) all the plants produced are genetically similar to the parent plant, so they keep all its desirable characteristics.
    Step-by-step solution →
    OR
    Q16(b) 5 marks
    What are sexually transmitted diseases ? Name any one sexually transmitted disease caused by virus and a bacterium. List any two contraceptive methods with their advantages.
    Show answer

    STDs spread through sexual contact; HIV-AIDS is viral and gonorrhoea bacterial; the condom and oral pills are two contraceptive methods with advantages.

    Sexually transmitted diseases are diseases that spread from an infected person to a healthy person through sexual contact. Caused by a virus: HIV-AIDS (or warts). Caused by a bacterium: gonorrhoea (or syphilis). Two contraceptive methods with their advantages: (1) Condom, a mechanical barrier - it stops the sperm from reaching the egg; it also helps to prevent the spread of STDs between partners and has no hormonal side-effects. (2) Oral contraceptive pills - they change the hormonal balance so that no egg is released; they are highly effective when taken regularly, need no device or surgery, and can be stopped whenever a child is wanted. Also acceptable: a copper-T or loop in the uterus, which protects for several years and can be removed; or surgery - vasectomy or tubectomy - which is permanent.
    Step-by-step solution →

Questions 17–24 · 1 mark each

  1. Q17 1 mark
    If an iron nail is kept in an aqueous solution of copper sulphate :
    1. (a)Iron gets precipitated in the solution.
    2. (b)Displacement reaction takes place.
    3. (c)Double-displacement reaction takes place.
    4. (d)No chemical reaction occurs.
    Show answer
    (b) Displacement reaction takes place.
    Step-by-step solution →
  2. Q18 1 mark
    The acid present in tamarind is :
    1. (a)Oxalic acid
    2. (b)Methanoic acid
    3. (c)Citric acid
    4. (d)Tartaric acid
    Show answer
    (d) Tartaric acid
    Step-by-step solution →
  3. Q19 1 mark
    Which of the following compounds is used as both an antacid and in a fire extinguisher ?
    1. (a)Sodium hydrogen carbonate
    2. (b)Sodium carbonate
    3. (c)Sodium hydroxide
    4. (d)Sodium chloride
    Show answer
    (a) Sodium hydrogen carbonate
    Step-by-step solution →
  4. Q20 1 mark
    Which of the following metal does not react with cold water, but reacts with steam ?
    1. (a)Sodium
    2. (b)Potassium
    3. (c)Iron
    4. (d)Calcium
    Show answer
    (c) Iron
    Step-by-step solution →
  5. Q21 1 mark
    Which of the following metals forms an amphoteric oxide ?
    1. (a)Calcium
    2. (b)Magnesium
    3. (c)Aluminium
    4. (d)Iron
    Show answer
    (c) Aluminium
    Step-by-step solution →
  6. Q22 1 mark
    Which of the following hydrocarbons will not undergo addition reactions ?
    1. (a)Ethane
    2. (b)Ethene
    3. (c)Ethyne
    4. (d)Propene
    Show answer
    (a) Ethane
    Step-by-step solution →
  7. Q23 1 mark
    The process used to convert vegetable oils to ghee (fats) is :
    1. (a)Saponification
    2. (b)Oxidation
    3. (c)Esterification
    4. (d)Hydrogenation
    Show answer
    (d) Hydrogenation
    Step-by-step solution →
  8. Q24 1 mark
    For Question number 24, two statements are given — one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer to this question from the codes (a), (b), (c) and (d) as given below.

    Assertion (A): Fat/oil-containing food items become rancid if they are kept in air for a long time.

    Reason (R): Oils and fats present in food items undergo slow oxidation in air.

    1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
    2. (b)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
    3. (c)Assertion (A) is true, but Reason (R) is false.
    4. (d)Assertion (A) is false, but Reason (R) is true.
    Show answer
    (a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
    Step-by-step solution →

Question 25 · 2 marks

  1. Q25 2 marks
    Define ionic compound. Write two properties of ionic compounds.
    Show answer

    Ionic compounds form by electron transfer from a metal to a non-metal, have high melting points, and conduct when molten or dissolved.

    Ionic compound: a compound formed by the transfer of electrons from a metal to a non-metal, so that it is made of positive and negative ions held together by strong electrostatic forces of attraction. It is also called an electrovalent compound. Example: sodium chloride, (). Two properties: (1) Ionic compounds have high melting and boiling points, because much energy is needed to overcome the strong attraction between the ions. (2) They conduct electricity in the molten state or in aqueous solution, where the ions can move, but not in the solid state. Other correct properties: they are hard but brittle solids, and they are generally soluble in water but insoluble in kerosene and petrol.
    Step-by-step solution →

Questions 26–27 · 3 marks each

  1. Q26 3 marks
    What happens when :
    1. (a)Lead nitrate powder is heated ?
    2. (b)Sodium sulphate solution is added to barium chloride solution ?
    3. (c)Hydrogen gas is passed over hot copper(II) oxide ?
    Show answer

    Lead nitrate gives brown fumes and lead oxide; a white precipitate of barium sulphate forms; black copper(II) oxide turns reddish-brown.

    (a) Lead nitrate decomposes on heating: brown fumes of nitrogen dioxide are given off along with oxygen, and lead(II) oxide is left behind. . This is a thermal decomposition reaction. (b) A white precipitate of barium sulphate is formed, and sodium chloride remains in solution. . This is a double displacement (precipitation) reaction. (c) The black copper(II) oxide turns reddish-brown as copper metal is formed, and water is produced. . This is a redox reaction: copper(II) oxide is reduced and hydrogen is oxidised.
    Step-by-step solution →
  2. Q27(a) 3 marks
    Define the following terms with an example :
    1. (i)Roasting
    2. (ii)Alloy
    3. (iii)Corrosion
    Show answer

    Roasting heats a sulphide ore in excess air; an alloy is a homogeneous mixture of metals; corrosion is slow attack on a metal.

    (i) Roasting: The process of heating a sulphide ore strongly in the presence of excess air to convert it into the oxide of the metal. Example: . (ii) Alloy: A homogeneous mixture of two or more metals, or of a metal and a non-metal. Example: brass, an alloy of copper and zinc (bronze, solder and steel are others). (iii) Corrosion: The slow eating away of a metal when its surface is attacked by substances around it, such as air, moisture or acids. Example: rusting of iron - in moist air iron gets coated with reddish-brown rust, hydrated iron(III) oxide, .
    Step-by-step solution →
    OR
    Q27(b) 3 marks
    Give reasons for the following :
    1. (i)Alloying is a very good method of improving the properties of a metal.
    2. (ii)Carbon cannot be used as a reducing agent to obtain highly reactive metals from their oxides.
    3. (iii)Silver articles become black after some time when exposed to air ?
    Show answer

    Alloying improves properties; reactive metals have more affinity for oxygen than carbon; silver turns black as silver sulphide forms.

    (i) Mixing a metal with other metals, or with a non-metal, changes its properties, so they can be improved to suit a use. Pure iron is soft, but with a small amount of carbon it becomes hard and strong steel, and with nickel and chromium it becomes stainless steel, which does not rust. Pure gold is too soft, so it is alloyed with silver or copper for jewellery. (ii) Highly reactive metals such as sodium, calcium, magnesium and aluminium have more affinity for oxygen than carbon has, so carbon cannot remove oxygen from their oxides. These metals are obtained by electrolytic reduction instead. (iii) Silver reacts with sulphur compounds (such as hydrogen sulphide) in the air and forms a black coating of silver sulphide: . This is the corrosion of silver.
    Step-by-step solution →

Question 28 · 4 marks

  1. Q28 4 marks
    Read the following passage and answer the questions that follow : Various substances can be classified as acids, bases and salts. Based on their strength, acids and bases are further classified as strong and weak. We can find this by using universal indicators, which shows different colours at different concentrations of hydrogen ions in a solution. A pH scale has been developed, which indicates acidic or basic nature of a solution, from 0 (very acidic) to 14 (very alkaline).
    1. (i)Define universal indicator.[1]
    2. (ii)The pH of solution ‘A’ is 6 and the pH of solution ‘B’ is 10. Which solution has more hydrogen ion concentration ?[1]
    3. (iii)(a)What is neutralisation reaction ? Give one example.[2]
    4. (iii)(b)OR : Four solutions A, B, C and D when tested with universal indicator showed pH as 5, 1, 9 and 13 respectively. Which solution is : (I) strongly alkaline, and (II) strongly acidic ?[2]
    Show answer

    Solution A (pH 6) has more hydrogen ions; a universal indicator is a mixture showing different colours; neutralisation gives salt and water.

    (i) A universal indicator is a mixture of several indicators that shows different colours at different concentrations of hydrogen ions in a solution; matching its colour against a chart gives the pH, and so shows how strongly acidic or basic the solution is. (ii) Solution ‘A’ (pH 6) has more hydrogen-ion concentration, because the lower the pH, the higher the hydrogen-ion concentration. (iii)(a) A neutralisation reaction is the reaction between an acid and a base to give a salt and water, for example . OR : (iii)(b) (I) D (pH 13) is strongly alkaline; (II) B (pH 1) is strongly acidic.
    Step-by-step solution →

Question 29 · 5 marks

  1. Q29(a) 5 marks
    1. (i)Give reason why carbon can neither form cation nor anion, but forms covalent compounds.
    2. (ii)What happens when : (I) a piece of sodium is dropped into ethanol ? (II) ethanol is heated with ethanoic acid in the presence of an acid ?
    3. (iii)Define soap. Why are soaps not effective in hard water ?
    Show answer

    Carbon shares electrons; sodium gives hydrogen and sodium ethoxide; ethanol with ethanoic acid gives an ester; soap forms insoluble scum in hard water.

    (i) Carbon (2, 4) has four valence electrons. It cannot form , because removing four electrons needs a very large amount of energy (six protons would be left holding only two electrons), and it cannot form , because a nucleus of six protons cannot hold ten electrons (four extra). So carbon shares its four valence electrons with other atoms and forms covalent compounds. (ii) (I) Sodium reacts with ethanol to form sodium ethoxide, and hydrogen gas is evolved: . (II) A sweet-smelling ester, ethyl ethanoate, is formed along with water (esterification): . (iii) Soap is the sodium or potassium salt of a long-chain carboxylic acid (e.g. sodium stearate, ). In hard water it reacts with the calcium and magnesium ions to form an insoluble scum, so the soap is wasted and does not lather or clean well.
    Step-by-step solution →
    OR
    Q29(b) 5 marks
    1. (i)Define the following terms with an example : (I) Unsaturated hydrocarbons (II) Substitution reaction (III) Saponification
    2. (ii)Why is ethanoic acid called glacial acetic acid ? Write one use of ethanoic acid.
    Show answer

    Unsaturated hydrocarbons have a double or triple bond; substitution swaps atoms; saponification splits an ester with alkali; pure ethanoic acid freezes at 290 K.

    (i) (I) Unsaturated hydrocarbons are hydrocarbons that contain at least one carbon-carbon double or triple bond, e.g. ethene, , or ethyne, . (II) A substitution reaction is one in which an atom or group of atoms in a molecule is replaced by another atom or group, e.g. . (III) Saponification is the reaction of an ester with an alkali (sodium hydroxide) to give an alcohol and the sodium salt of the carboxylic acid; with fats or oils the salt formed is soap. E.g. . (ii) Pure ethanoic acid melts at 290 K (about ), so it often freezes into ice-like crystals during winter in cold climates; hence it is called glacial acetic acid. Use: a 5-8% solution of ethanoic acid in water is vinegar, used as a preservative in pickles.
    Step-by-step solution →

Questions 30–32 · 1 mark each

  1. Q30 1 mark
    A convex lens and a concave lens having focal lengths 10 cm and 20 cm respectively are placed in contact with each other. Which of the following statements is correct about the lens combination ?
    1. (a)It will behave like a plane glass slab.
    2. (b)It will behave like a convex lens.
    3. (c)It will behave like a concave lens.
    4. (d)It will behave like a cylindrical lens.
    Show answer
    (b) It will behave like a convex lens.
    Step-by-step solution →
  2. Q31 1 mark
    The part of eye which causes change in the focal length of eye lens to provide it exceptional accommodation power is :
    1. (a)Aqueous humour
    2. (b)Ciliary muscles
    3. (c)Pupil
    4. (d)Iris
    Show answer
    (b) Ciliary muscles
    Step-by-step solution →
  3. Q32 1 mark
    For Question number 32, two statements are given — one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer to this question from the codes (a), (b), (c) and (d) as given below.

    Assertion (A): Nichrome is an alloy which is commonly used in electrical heating devices like electric irons.

    Reason (R): The resistivity of nichrome is high and its resistance decreases with an increase in temperature.

    1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
    2. (b)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
    3. (c)Assertion (A) is true, but Reason (R) is false.
    4. (d)Assertion (A) is false, but Reason (R) is true.
    Show answer
    (c) Assertion (A) is true, but Reason (R) is false.
    Step-by-step solution →

Questions 33–34 · 2 marks each

  1. Q33 2 marks
    The values of refractive indices of two optical media X and Y are 1.44 and 1.30, respectively. Compare the values of the following quantities pertaining to them :
    1. (a)Speed of light
    2. (b)Angle of refraction for same angle of incidence Justify your answer.
    Show answer

    Light travels faster in Y than in X, and for the same angle of incidence the angle of refraction is smaller in X.

    (a) Light travels faster in Y than in X. Since , m/s and m/s: the larger refractive index belongs to the optically denser medium, X, in which light is slower. (b) For the same angle of incidence the angle of refraction is smaller in X than in Y. By Snell's law , and gives , so : light bends more towards the normal in the optically denser medium X.
    Step-by-step solution →
  2. Q34(a) 2 marks
    Name a phenomenon taking place in nature where light rays are dispersed. When, where and how does this phenomenon happen ?
    Show answer

    A rainbow: seen after rain, opposite the Sun, when sunlight is refracted, dispersed and internally reflected in water droplets.

    The phenomenon is the rainbow. When: it is seen just after a rain shower (or in the spray of a waterfall or fountain) while the Sun is shining, with the Sun behind the observer, usually in the morning or late afternoon when the Sun is low. Where: in the sky in the direction opposite to the Sun, formed by tiny water droplets suspended in the air in front of the observer. How: each droplet acts like a small prism. Sunlight entering it is refracted and dispersed into its colours, is reflected internally at the back of the drop, and is refracted again as it comes out. Because each colour leaves at a slightly different angle, different colours reach the eye from different drops and a spectrum is seen as an arc, red on the outside and violet on the inside.
    Step-by-step solution →
    OR
    Q34(b) 2 marks
    Match the items given in Column I with the correct option given in Column II :
    Show answer
    1 - (s), 2 - (p), 3 - (q), 4 - (r). Mirror: Reflection of light; Lens: Refraction of light; Prism: Dispersion of light; Scattering of light: Tyndall effect.
    Step-by-step solution →

Questions 35–37 · 3 marks each

  1. Q35 3 marks
    The various positions of an object from a convex lens and the relative sizes of the images formed in each position are tabulated below. Look at the data carefully and answer the questions that follow the table :
    1. (a)What is the focal length of the lens ?
    2. (b)What is the nature of the images formed in case of observation 3 and 4 ?
    S.No.Position of object from lens (cm)Relative size of image (cm)
    1.45Smaller than object
    2.30Same size as object
    3.20Magnified
    4.10Magnified
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    cm; observation 3 gives a real, inverted, magnified image and observation 4 a virtual, erect, magnified image.

    (a) The focal length of the lens is cm. In observation 2 the image is the same size as the object, which happens with a convex lens only when the object is at ; so cm and cm. (b) Observation 3 (object at cm, between and ): the image is real, inverted and magnified, formed beyond on the other side of the lens ( cm). Observation 4 (object at cm, between and the optical centre): the image is virtual, erect and magnified, formed on the same side of the lens as the object ( cm), and it cannot be obtained on a screen.
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  2. Q36 3 marks
    Two persons, A and B are using lenses of power D and D respectively in their spectacles. Write the names of eye defects from which A and B are suffering. Write two causes for each defect of vision.
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    A has hypermetropia (convex lens, long eye-lens focal length or small eyeball); B has myopia (concave lens, excessive lens curvature or long eyeball).

    A (power D, a convex lens) suffers from hypermetropia (long-sightedness or far-sightedness): nearby objects are not seen clearly because their image forms behind the retina. Two causes: (i) the focal length of the eye lens is too long; (ii) the eyeball has become too small. B (power D, a concave lens) suffers from myopia (short-sightedness or near-sightedness): distant objects are not seen clearly because their image forms in front of the retina. Two causes: (i) excessive curvature of the eye lens, which makes its focal length too short; (ii) elongation of the eyeball.
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  3. Q37 3 marks
    1. (a)At every electricity point in the different rooms of a house, there is a potential difference of 220 V. How is this possible ? Write any one benefit of it.
    2. (b)An electric heater rated 2 kW; 220 V is used in a room having electric circuit of current rating of 5 A. What will happen when you switch on the circuit ? Justify your answer with reason.
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    The points are in parallel, so each gets 220 V; the heater draws 9.09 A, above the 5 A rating, so the fuse blows.

    (a) All the electricity points (sockets and appliances) in the rooms are connected in parallel between the live wire and the neutral wire of the mains. In a parallel connection the potential difference across every branch equals the supply voltage, so each point gets the full V. Benefit (any one): each appliance works at the full voltage it is designed for, and each can be switched on or off independently without affecting the others. (b) The heater draws A, which is more than the A current rating of the circuit. The circuit is overloaded, so its fuse melts (or the circuit breaker trips) and the supply is cut off; the heater cannot be used on this circuit and should be connected to the A power circuit.
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Question 38 · 4 marks

  1. Q38 4 marks
    Read the following passage and answer the questions that follow : Bhoumik was playing with a magnetic compass near a current carrying spring-like device. He observed that the compass needle shows deflection whenever he goes close to the device. After observing it, he started running around the device. Now, he observed that the compass needle is continuously changing its direction and tries to orient itself along the North-South direction of the Earth.
    1. (i)What is the similarity in the behaviour of a freely suspended bar magnet and a magnetic compass ?[1]
    2. (ii)How can the magnitude and direction of the magnetic field of a solenoid be changed ?[1]
    3. (iii)(a)Compare the magnetic field due to a current-carrying solenoid and a current-carrying straight wire made by stretching a solenoid.[2]
    4. (iii)(b)OR : When a moving electron enters in a magnetic field, what will happen to its motion ? State the law required to explain your observation of moving electron in a magnetic field.[2]
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    Both settle North-South; current sets the field's size and direction; a solenoid has a strong uniform field with poles, a straight wire weak circles.

    (i) A magnetic compass is a small, freely pivoted bar magnet, so both behave alike: each comes to rest along the North-South direction with its north pole pointing towards the geographic North, and each is deflected when a magnet or a current-carrying conductor is brought near it. (ii) The magnitude of the field is changed by changing the current through the solenoid - a larger current (or more turns, or a soft iron core inside) gives a stronger field; the direction is reversed by reversing the direction of the current, which interchanges the north and south ends. (iii)(a) Solenoid: the field lines inside are parallel straight lines, so the field inside is strong and uniform; outside it is like that of a bar magnet, with a north pole at one end and a south pole at the other - the field lines run from the north pole to the south pole outside the solenoid and from the south pole to the north pole inside it. Straight wire (the solenoid stretched out): the field lines are concentric circles around the wire; the field is much weaker, is not uniform - it decreases with distance from the wire - and there are no poles. (iii)(b) The electron experiences a force at right angles to both its motion and the field, so it is deflected from its straight path: its direction of motion changes (it moves along a circular arc if it enters at right angles to the field) while its speed stays the same; an electron moving along the field lines is not deflected. The law is Fleming's left-hand rule: with the thumb, forefinger and middle finger of the left hand mutually perpendicular, if the forefinger points along the field and the middle finger along the current, the thumb gives the direction of the force - for an electron the current is opposite to its motion.
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Question 39 · 5 marks

  1. Q39(a) 5 marks
    1. (i)What is meant by the resistance of a conductor ? Derive an expression for the equivalent resistance of an electric circuit in which two resistors, and are connected in parallel.
    2. (ii)Calculate the power consumed per second if two resistors, and are connected in (I) a series combination, and (II) a parallel combination, with a battery of V potential difference.
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    Parallel resistors obey ; power consumed per second is about 10.67 W in series and 48 W in parallel.

    (i) Resistance is the property of a conductor by which it opposes the flow of electric current through it; it is the ratio of the potential difference across the conductor to the current through it, , and its SI unit is the ohm (). Circuit diagram: and are both joined between the same two points A and B, and a battery of potential difference is connected across A and B, the current dividing into through and through (as in the figure). Each resistor has the same across it and the total current is , so , which gives , that is, . (ii) (I) Series: and A, so W - about J of energy consumed every second. (II) Parallel: and A, so W - J of energy consumed every second.
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    OR
    Q39(b) 5 marks
    1. (i)Name the device which (I) helps to change the electric current in the given electric circuit and (II) breaks the circuit during short-circuiting.
    2. (ii)State Ohm’s law and write the factors on which the resistance of a given conductor depends.
    3. (iii)Find out the length of a wire of resistance , if the diameter of the wire is cm and resistivity of the material is . [Given : ]
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    A rheostat and a fuse are the devices, resistance depends on four factors, and the wire is m long.

    (i) (I) A rheostat (a variable resistance), which changes the resistance and hence the current in the circuit. (II) An electric fuse (or a miniature circuit breaker), whose wire melts when the large short-circuit current flows and so breaks the circuit. (ii) Ohm's law: the potential difference across the ends of a metallic conductor is directly proportional to the current flowing through it, provided its temperature remains the same; . The resistance of a conductor depends on its length (), its area of cross-section (), the nature of its material (its resistivity ) and its temperature, so that . (iii) cm m, m, and m.
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