Question 1
  1. A moment of couple has a tendency to rotate the body in an anti-clockwise direction. Then the moment of couple is taken as:
    1. Positive
    2. Negative
    3. Maximum
    4. Zero
    View Answer
    Correct Answer is (a).

    If a couple has the tendency to rotate the body in an anti-clockwise direction, then the moment of couple is taken as positive.

  2. The kinetic energy of a given body depends on the:
    1. position
    2. centre of gravity of the body
    3. momentum
    4. displacement
    View Answer
    Correct Answer: (c) momentum.
    img
  3. For burning of coal in a thermoelectric station, the energy conversion taking place is:
    1. Chemical to heat to mechanical
    2. Chemical to heat to mechanical to electrical
    3. Chemical to heat to light
    4. Heat to chemical to mechanical
    View Answer
    Correct Answer: (b) Chemical to heat to mechanical to electrical.

    Coal (chemical energy) burns to produce heat and light energy which helps in the rotation of the turbine (Mechanical energy) which finally converts into electrical energy.

  4. A nucleus of an atom consists of 146 neutrons and 95 protons. It decays after emitting an alpha particle. How many protons and neutrons are left in the nucleus after an alpha emission?
    1. protons = 93, neutrons = 144
    2. protons = 95, neutrons = 142
    3. protons = 89, neutrons = 144
    4. protons = 89, neutrons = 142
    View Answer
    Correct Answer: (a) protons = 93, neutrons = 144.

    During α emission, 2 protons and 2 neutrons are lost:
    Protons left = 95 − 2 = 93
    Neutrons left = 146 − 2 = 144

  5. Assertion: Infrared radiations travel long distances through dense fog and mist. Reason: Infrared radiations undergo minimal scattering in Earth's atmosphere.
    1. Both assertion and reason are true.
    2. Both assertion and reason are false.
    3. Assertion is false but reason is true.
    4. Assertion is true but reason is false.
    View Answer
    Correct Answer: (a) Both assertion and reason are true.

    Assertion: this is why they are used in devices like night-vision cameras.
    Reason: Wavelength of IR- radiations are longer than visible light.

  6. For a convex lens, the minimum distance between an object and its real image in terms of focal length (f) of a given lens must be:
    1. 1.5 f
    2. 2.5 f
    3. 2 f
    4. 4 f
    View Answer
    Correct Answer is (d): 4 f

    Let d = distance between object and real image
    x = distance of the object from the lens
    d - x = distance of the image from the lens
    LaTeX equation: Lens formula and derivation for d = 4fSince d cannot be zero, the minimum distance is \( d = 4f \).

  7. Two sound waves X and Y have the same amplitude and the same wave pattern, but their frequencies are 60 Hz and 120 Hz respectively, then:
    1. X will be shriller and Y will be grave.
    2. X will be grave and Y will be shriller.
    3. X will differ in quality than Y.
    4. X is louder than Y.
    View Answer
    Correct Answer is (b): X will be grave and Y will be shriller

    X= grave (less frequency)
    Y= shriller (more frequency)

  8. Vibrations produced in a body under the influence of the periodic force is:
    1. Forced vibrations
    2. Resonant vibrations
    3. Damped vibrations
    4. Sympathetic vibrations
    View Answer
    Correct Answer is (a): Forced vibrations

    The vibrations of a body that occur under the influence of an external periodic force acting on it are called forced vibrations.

  9. The graph of voltage v/s current for four different materials is as shown below:LaTeX equation: Lens formula and derivation for d = 4fWhich of these four materials would be used for making the coil of a toaster?
    1. Q
    2. S
    3. P
    4. R
    View Answer
    Correct Answer is (c): P

    ∵ V = IR
    ∴ V α R
    To make the coil of a toaster, resistance should be high (to produce more heat). And for that, voltage should be more.
    ∴ Resistance of P is more.

  10. According to old convention the colour of the earth wire is:
    1. Black
    2. Green
    3. Yellow
    4. Red
    View Answer
    Correct Answer is (b): Green
  11. Lenz's law is based on the law of conservation of:
    1. Force
    2. Charge
    3. Mass
    4. Energy
    View Answer
    Correct Answer is (d): Energy

    Lenz's law is based on the law of conservation of energy. It shows that the mechanical energy is spent in doing work against the opposing force experienced by the moving magnet, and it is transformed into electrical energy due to which current flows in the solenoid.

  12. Heat capacity of the body is:
    1. The energy needed to melt the body without the change in its temperature.
    2. The energy needed to raise the temperature of the body by 1°C.
    3. The increase in the volume of the body when its temperature increases by 1°C.
    4. The total amount of internal energy that is constant.
    View Answer
    Correct Answer is (b): The energy needed to raise the temperature of the body by 1°C.

    Heat capacity is the total amount of heat required to raise the body's temperature by 1°C. It depends on the mass and material of the body.

  13. The amount of heat energy required to melt a given mass of a substance at its melting point without a rise in its temperature is called:
    1. Specific heat capacity
    2. Specific latent heat of fusion
    3. Latent heat of fusion
    4. Specific latent heat of freezing
    View Answer
    Correct Answer: (C) Latent heat of fusion

    Latent heat of fusion is the amount of heat energy required to change a substance from solid to liquid at its melting point without any change in temperature. This breaks the bonds between particles, allowing the phase change to occur.

  14. When a ray of light enters from a denser medium to a rarer medium then:
    1. The light ray bends towards the normal.
    2. The speed of light increases.
    3. The angle of incidence is greater than the angle of refraction.
    4. Its wavelength decreases.
    View Answer
    Correct Answer: (B) The speed of light increases

    When a ray of light moves from a denser medium to a rarer medium, the ray bends away from the normal, and the speed of light increases. Additionally, the wavelength of the light increases rather than decreases in the rarer medium.

  15. An endoscope uses optical fiber to transmit high-resolution images of internal organs without loss of information. The phenomenon of light that governs the functioning of the optical fiber is:
    1. Refraction
    2. Reflection
    3. Scattering
    4. Total internal reflection
    View Answer
    Correct Answer: (D) Total internal reflection

    Total internal reflection is the phenomenon that allows light to be transmitted through optical fibers with minimal loss. Beyond a certain angle (the critical angle), all the light is reflected back within the medium, enabling efficient transmission in devices like endoscopes.


Question 2
    1. Name the principle on which the lever works.
    2. Which radiations that are emitted during the decay of a nucleus, having the highest penetrating power?
    3. Does the emission of the above-mentioned radiation result in a change in the mass number?
    View Answer
    Answers:
    • (a) The lever works on the principle of moments. According to this principle, in the equilibrium position of levers, the moment of load about the fulcrum must be equal to the moment of effort about the fulcrum, and the two moments must act in opposite directions.
    • (b) Gamma radiations have the highest penetrating power among the radiations emitted during nuclear decay.
    • (c) The emission of gamma radiations does not result in a change in the mass number, as gamma radiations have no charge or mass.
  2. A metre rod of copper and steel is shown in the diagram. The weights of copper and steel are 10 N and 8 N, respectively. On which part does the centre of gravity lie (0 to 50 or 50 to 100)? Justify your answer.img
    View Answer
    Answer:
    • (a) The centre of gravity of the rod lies between 0 to 50.
    • Justification:In equilibrium, the principle of moments is applied:
      F1 × D1 = F2 × D2
      Here, F1 > F2, which implies D1 < D2.
      Since the weight of the copper part (10 N) is greater than the weight of the steel part (8 N), the centre of gravity shifts closer to the copper end, i.e., between 0 and 50.
  3. A lever is shown below: Identify the type of lever. Calculate its mechanical advantage.img
    View Answer
    Answer:
    • (a) This is a Type III lever (as effort is in between load and fulcrum).
    • (b)
      LaTeX equation: Mechanical Advantage calculation
  4. Two bodies A and B have the same kinetic energies. Compare their velocities if the mass of A is 4 times the mass of B.
    View Answer
    Answer:
    LaTeX equation: Kinetic energy and velocity relationship derivation
  5. Draw a graph of potential energy v/s height from the ground for a body thrown vertically upwards.
    View Answer
    Answer:

    ∵ PE = mgh
    PE α h

    This will be a straight-line graph.

    hPE
  6. Two copper wires A and B are of the same thickness and are at room temperature. If the length of A is twice the length of B, then:
    1. Compare their resistances
    2. Compare their resistivities
    View Answer
    Answer:
    LaTeX equation: Resistance ratio derivation based on length and cross-sectional area


    (ii) Both the wires will have the same specific resistivities, as resistivity depends on the nature of the material, and here both the wires are made of copper.


  7. (a) Name the waves used for echo depth sounding.
    (b) Give one reason for their use in the above application.
    View Answer
    Answer:

    (a) The waves used for echo depth sounding are 'Ultrasonic waves'.

    (b) Ultrasonic waves are used for echo depth sounding due to the following reasons: (any one)

    • They are more energetic than audible sound (frequency &gt 20 kHz) and can travel undeviated through long distances.
    • They can be confined to a narrow beam.
    • They are not easily absorbed in a medium.

Question 3

  1. (a) Refer to the diagram given below. A lens with two different refractive indices is shown. If rays are coming from a distant object, then how many images will be seen?img

    (b) A glass lens always forms a virtual, erect, and diminished image of an object kept in front of it. Identify the lens.
    View Answer
    Answer:

    (a) A lens with two different refractive indices will have two different foci and hence two different images will be seen. If μ1 < μ2, then f1 > f2, and vice versa.

    img

    (b) A lens always forms a virtual, erect, and diminished image when an object is kept in front of it. Hence, it is a concave lens.

    LaTeX equation: μ is inversely proportional to f

  2. It is observed that the house circuits are arranged in a parallel combination. Give two advantages of this arrangement.

    View Answer
    Answer:

    Advantages of arrangement of house circuit in a parallel arrangement are as follows:

    • Each appliance gets connected to 220 V power supply (equal to its voltage rating) for its normal working.
    • Each appliance operates independently without being affected by the presence or working of the other appliance.

  3. A transformer is used to change a high alternating e.m.f. to a low alternating e.m.f. of the same frequency.

    1. Identify the type of transformer used for the above purpose.
    2. State whether the turns ratio of the above transformer is =1 or >1 or < 1.
    View Answer
    Answer:

    (a) To change the high alternating e.m.f. to a low alternating e.m.f. of the same frequency, a step-down transformer is used.

    (b) In a step-down transformer:

    • Number of turns in secondary coil < Number of turns in primary coil
    • Therefore, turn ratio (n) < 1

  4. A solid of mass 60 g at 100°C is placed in 150 g of water at 20°C. The final steady temperature is 25°C. Calculate the heat capacity of the solid. (Specific heat capacity of water = 4.2 J g⁻¹ K⁻¹)

    View Answer
    Answer: