Physics MCQ Practice 12 — Science Foundation Course for Class 11 & 12

1. A car accelerates uniformly from 10 m/s to 30 m/s in 5 seconds. The distance covered is:

(a) 50 m (b) 100 m (c) 150 m (d) 200 m

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Correct Answer: (b) 100 m

Explanation:
s = ut + ½at ², a = 4 m/s² → s = 10×5 + ½×4×25 = 100 m

2. The value of g at the centre of Earth is:

(a) Zero (b) 9.8 m/s² (c) 4.9 m/s² (d) Infinite

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Correct Answer: (a) Zero

Explanation:
At the centre of Earth, net gravitational force is zero

3. Three resistors 2 Ω, 3 Ω and 6 Ω are connected in parallel. Equivalent resistance is:

(a) 11 Ω (b) 1 Ω (c) 2 Ω (d) 6 Ω

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Correct Answer: (b) 1 Ω

Explanation:
1/R = 1/2 + 1/3 + 1/6 = 1 → R = 1 Ω

4. The velocity of sound in air increases with:

(a) Decrease in temperature (b) Increase in humidity (c) Decrease in pressure (d) All of the above

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Correct Answer: (b) Increase in humidity

Explanation:
Velocity increases with humidity (density decreases)

5. The magnetic field due to a straight current-carrying wire at a distance r is 0.1 T. If current is doubled and distance halved, new field is:

(a) 0.1 T (b) 0.2 T (c) 0.4 T (d) 0.8 T

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Correct Answer: (c) 0.4 T

Explanation:
B ∝ I/r → I×2, r/2 → B becomes 4 times = 0.4 T

6. A concave lens of focal length 20 cm forms an image at 10 cm from the lens. The object distance is:

(a) 20 cm (b) -20 cm (c) 10 cm (d) -40 cm

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Correct Answer: (b) -20 cm

Explanation:
1/v - 1/u = 1/f (concave f negative) → u = -20 cm

7. In a step-up transformer, the transformation ratio is 1:4. If input voltage is 220 V, output voltage is:

(a) 55 V (b) 880 V (c) 440 V (d) 110 V

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Correct Answer: (b) 880 V

Explanation:
V_s = V_p × (N_s/N_p) = 220 × 4 = 880 V

8. The most stable nucleus is:

(a) Uranium (b) Iron (c) Lead (d) Hydrogen

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Correct Answer: (b) Iron

Explanation:
Iron has highest binding energy per nucleon

9. If the radius of Earth is reduced to half without changing mass, g becomes:

(a) Same (b) Half (c) Double (d) Four times

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Correct Answer: (d) Four times

Explanation:
g = GM/R² → R halved → g becomes 4 times

10. The unit of surface tension is:

(a) N/m (b) N m (c) J/m² (d) Both (a) and (c)

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Correct Answer: (d) Both (a) and (c)

Explanation:
Surface tension = force/length = energy/area