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CBSE Class 10 Science 2024 — Paper 31(B)

80 marks · 3 hours · 39 questions (48 with the OR choices)

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Questions 1–20 · 1 mark each

  1. Q1 1 mark
    A ray of light is incident on a plane mirror at an angle of incidence of . The deviation in the ray produced by the mirror is :
    1. (a)
    2. (b)
    3. (c)
    4. (d)
    Show answer
    (d)
    Step-by-step solution →
  2. Q2 1 mark
    For an object, a convex mirror always forms an image which is :
    1. (a)Virtual, erect and magnified
    2. (b)Virtual, erect and diminished
    3. (c)Virtual, inverted and diminished
    4. (d)Real, erect and diminished
    Show answer
    (b) Virtual, erect and diminished
    Step-by-step solution →
  3. Q3 1 mark
    Two resistors of and are connected in parallel in a circuit. If a current of ampere is flowing through the circuit, the current flowing through the resistor is :
    1. (a) ampere
    2. (b) ampere
    3. (c) ampere
    4. (d) ampere
    Show answer
    (d) ampere
    Step-by-step solution →
  4. Q4 1 mark
    Two wires of same metal have the same length but their cross-sectional areas are in the ratio of . They are joined in series. The resistance of the thicker wire is . The total resistance of the combination is :
    1. (a)
    2. (b)
    3. (c)
    4. (d)
    Show answer
    (b)
    Step-by-step solution →
  5. Q5 1 mark
    Consider the following statements : i. Ciliary muscles adjust for changing the intensity of light entering the eye. ii. Myopic eye can be corrected by converging lenses of suitable power. iii. The function of the pupil is to regulate the quantity of light entering the eye. iv. When ciliary muscles are completely relaxed, the focal length of the eye lens is maximum. The correct statements are :
    1. (a)i, ii and iv
    2. (b)i, ii and iii
    3. (c)iii and iv
    4. (d)ii and iv
    Show answer
    (c) iii and iv
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  6. Q6 1 mark

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  7. Q7 1 mark

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  8. Q8 1 mark

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  9. Q9 1 mark

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  10. Q10 1 mark

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  11. Q11 1 mark

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  12. Q12 1 mark

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  13. Q13 1 mark

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  14. Q14 1 mark

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  15. Q15 1 mark

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  16. Q16 1 mark

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  17. Q17 1 mark
    For Questions number 17 and 20, 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): The intensity of the magnetic field produced at the centre of a current carrying circular coil increases on increasing the number of turns in the coil.

    Reason (R): The current that flows in each turn of the coil has the same magnitude and same direction and the magnetic field, due to each turn, just adds up.

    1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
    2. (b)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
    3. (c)Assertion (A) is true and Reason (R) is false.
    4. (d)Assertion (A) is false and Reason (R) is true.
    Show answer
    (a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
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  18. Q18 1 mark

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  19. Q19 1 mark

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  20. Q20 1 mark

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Questions 21–26 · 2 marks each

  1. Q21(a) 2 marks
    List four properties of the images formed by a plane mirror.
    Show answer

    The image is virtual, erect, the same size as the object, and as far behind the mirror as the object is in front.

    Any four of these: (1) The image is virtual: it cannot be obtained on a screen. (2) It is erect. (3) It is of the same size as the object. (4) It is formed as far behind the mirror as the object is in front of it. (5) It is laterally inverted.
    Step-by-step solution →
    OR
    Q21(b) 2 marks
    Write the definitions of the following terms in the context of a concave mirror:
    1. (i)Pole
    2. (ii)Centre of curvature
    3. (iii)Radius of curvature
    4. (iv)Principal axis
    Show answer

    Pole is the mirror's centre, C is its sphere's centre, R equals PC, and the principal axis joins P and C.

    (i) Pole: The centre of the reflecting surface of the concave mirror is called its pole (P); it lies on the surface of the mirror. (ii) Centre of curvature: The reflecting surface of the mirror is a part of a sphere, and the centre of that sphere is the centre of curvature (C); it is not a part of the mirror and lies in front of a concave mirror. (iii) Radius of curvature: The radius of the sphere of which the reflecting surface forms a part is the radius of curvature (R); it equals the distance PC. (iv) Principal axis: The straight line passing through the pole and the centre of curvature is the principal axis; it is normal to the mirror at its pole.
    Step-by-step solution →
  2. Q22 2 marks
    Write the shape of the magnetic field produced by a current carrying straight conductor. State the rule to find the direction of this field.
    Show answer

    The field lines are concentric circles centred on the conductor; the direction is given by the right-hand thumb rule.

    Shape: The magnetic field lines around a current-carrying straight conductor are concentric circles with the conductor at their common centre, lying in planes perpendicular to the conductor; they are farther apart away from the wire, where the field is weaker. Rule: The right-hand thumb rule: if the conductor is held in the right hand with the thumb pointing in the direction of the current, the fingers wrapped around the conductor give the direction of the magnetic field lines.
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  3. Q23(a) 2 marks

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    Q23(b) 2 marks

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  4. Q24 2 marks

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  5. Q25 2 marks

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  6. Q26(a) 2 marks

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    Q26(b) 2 marks

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Questions 27–33 · 3 marks each

  1. Q27(a) 3 marks
    1. (i)How does an electric fuse prevent the circuit and the appliances from possible damage due to short circuiting or overloading?
    2. (ii)How is the type of current used in household supply different from the one given by dry cells or storage batteries?
    3. (iii)For distant transmission of electric power, an alternating current (ac) is considered to be advantageous over direct current (dc). Why?
    Show answer

    A fuse melts to break the circuit; household supply is AC, cells give DC; AC suits long-distance transmission.

    (i) A fuse is a wire of a metal or an alloy of appropriate melting point, connected in series with the live wire. When short-circuiting or overloading makes the current rise above its rated value, the heat produced in the fuse wire () melts it; the circuit breaks and the unduly high current stops, so the wiring and the appliances are not damaged. (ii) Household supply is alternating current (AC), which reverses its direction periodically (in India at a frequency of Hz, changing direction every s), whereas dry cells and storage batteries give direct current (DC), which always flows in one direction. (iii) AC can be transmitted over long distances without much loss of energy: its voltage can easily be stepped up for transmission, so the same power is carried by a small current and the heating loss in the wires, , is small; the voltage is stepped down again before it reaches homes. The voltage of DC cannot be changed as easily.
    Step-by-step solution →
    OR
    Q27(b) 3 marks
    (i) A straight conductor is suspended horizontally with its axis perpendicular to the magnetic field of a strong horseshoe magnet. The conductor gets displaced towards the right when a steady current is passed through it. What will happen to the displacement of the conductor if the :
    1. (1)Polarity of the horseshoe magnet is reversed ?
    2. (2)Direction of current in the conductor is reversed ?
    3. (3)Current through the conductor is increased ? (ii) Name and state the rule for determining the direction of force on a current carrying conductor placed in a magnetic field.
    Show answer

    Reversing the poles or the current moves the conductor left; a larger current moves it further right; Fleming's left-hand rule.

    (i) (1) The displacement is reversed: the conductor is now displaced towards the left, because reversing the poles reverses the magnetic field. (2) The displacement is again reversed: the conductor is displaced towards the left, because the force reverses when the current reverses. (3) The conductor is still displaced towards the right, but by a larger amount, because a larger current experiences a larger force. (ii) Fleming's left-hand rule. Stretch the thumb, forefinger and middle finger of the left hand so that they are mutually perpendicular. If the forefinger points in the direction of the magnetic field and the middle finger in the direction of the current, then the thumb points in the direction of the force on (motion of) the conductor.
    Step-by-step solution →
  2. Q28 3 marks
    When and where does a rainbow appear in the sky ? List the phenomena of light in proper sequence which occurs during the formation of a rainbow. Why can a rainbow not be seen from the surface of the moon ?
    Show answer

    A rainbow forms after rain, opposite the Sun; the moon has no atmosphere, hence no water droplets and no rainbow.

    A rainbow appears in the sky after a rain shower, when the Sun is shining and tiny water droplets are still present in the atmosphere. It is always seen in the direction opposite to the Sun, that is, with the Sun behind the observer. The phenomena, in sequence: (1) Refraction of sunlight, with dispersion into its colours, as it enters a water droplet; (2) Internal reflection of the light at the back surface of the droplet; (3) Refraction again, with further dispersion, as the light comes out of the droplet towards the observer. A rainbow cannot be seen from the surface of the moon because the moon has no atmosphere, so there are no water droplets suspended above it to refract, disperse and internally reflect the sunlight.
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  3. Q29(a) 3 marks

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    Q29(b) 3 marks

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  4. Q30 3 marks

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  5. Q31(a) 3 marks

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    Q31(b) 3 marks

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  6. Q32 3 marks

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  7. Q33(a) 3 marks

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    Q33(b) 3 marks

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Questions 34–36 · 5 marks each

  1. Q34(a) 5 marks
    1. (i)Write the relation between resistivity () and resistance () for a uniform metallic conductor of length () and area of cross-section (). Use this relation to obtain the SI unit of resistivity.
    2. (ii)The resistance of a metallic wire of m is . If the radius of the wire is mm, find the resistivity of the metal of the wire.
    Show answer

    gives the SI unit of resistivity as ; the wire's resistivity is about .

    (i) , so ; the SI unit of resistivity is (ohm metre). (ii) , so .
    Step-by-step solution →
    OR
    Q34(b) 5 marks
    1. (i)Obtain an expression for the amount of heat produced in a conductor of resistance when a steady current flows through it for a time .
    2. (ii)An electrical heater of resistance draws a steady current of A from the service mains for hours. Find the power of this heater and the amount of energy consumed by the heater in kilowatt hour.
    Show answer

    Heat produced is ; the heater has power W and consumes kWh in 2 hours.

    (i) In time a charge moves through the potential difference , so the energy supplied, which appears as heat, is ; with this gives (Joule's law of heating). (ii) Power W; energy consumed kWh.
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  2. Q35 5 marks

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  3. Q36(a) 5 marks

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    Q36(b) 5 marks

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Questions 37–39 · 4 marks each

  1. Q37 4 marks
    A student has three convex lenses A, B and C of different focal lengths. He wants to observe the images formed by these lenses on a screen by placing a candle flame at different distances as given in following table :
    Case No.LensFocal LengthObject Distance
    1A50 cm25 cm
    2B20 cm60 cm
    3C15 cm30 cm
    1. (i)List two properties of the image formed by the lens B in case no. 2.[1]
    2. (ii)In which one of the three cases given above will the lens form a real image of the same size as the object and why ?[1]
    3. (iii)(a)Name the type of lens presented by opticians for the correction of hypermetropia. State the role of such lenses in correcting the vision of the person suffering from this defect.[2]
    4. (iii)(b)OR : Use Lens formula to find the distance of the image formed from the optical centre of the lens A in case no. 1.[2]
    Show answer

    Image is real and inverted; case 3 gives a real, same-size image; hypermetropia needs a convex lens; OR cm.

    (i) Case 2: the image is real and inverted (it is also diminished, formed between and at cm, with ). (ii) Case 3: the candle is at cm of lens C, that is, at , so the real, inverted image forms at and is of the same size ( cm, ). (iii)(a) A convex (converging) lens of suitable power. It supplies the additional focusing power, so light from a near object, which the eye alone focuses behind the retina, is focused on the retina. (iii)(b) With cm and cm, , so cm: the image is cm from the optical centre, on the same side as the candle (virtual and erect, ).
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  2. Q38 4 marks

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  3. Q39 4 marks

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