Physics MCQ Practice 17 — Science Foundation Course for Class 11 & 12

1. A stone is dropped from a height of 45 m. The time taken to reach the ground (g=10 m/s²) is:

(a) 3 s (b) 4.5 s (c) 9 s (d) 2 s

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Correct Answer: (a) 3 s

Explanation:
h = ½gt² → 45 = 5t² → t = 3 s

2. The escape velocity from Earth is 11.2 km/s. The escape velocity from a planet with double mass and half radius is:

(a) 11.2 km/s (b) 22.4 km/s (c) 15.8 km/s (d) 5.6 km/s

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Correct Answer: (b) 22.4 km/s

Explanation:
v_esc ∝ √(M/R) → √(2M / (R/2)) = √4 = 2 times = 22.4 km/s

3. The equivalent capacitance of three 6 μF capacitors in parallel is:

(a) 18 μF (b) 2 μF (c) 6 μF (d) 3 μF

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Correct Answer: (a) 18 μF

Explanation:
Parallel combination: C = 6 + 6 + 6 = 18 μF

4. The frequency of a sound wave is 500 Hz. The time period is:

(a) 0.002 s (b) 0.5 s (c) 2 s (d) 0.02 s

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Correct Answer: (a) 0.002 s

Explanation:
T = 1/f = 1/500 = 0.002 s

5. The magnetic field at the centre of a current carrying circular coil is proportional to:

(a) Radius (b) 1/Radius (c) Radius² (d) 1/Radius²

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Correct Answer: (b) 1/Radius

Explanation:
B = μ₀ I / (2R) ∝ 1/R

6. A convex lens of focal length 25 cm forms a real image at 50 cm. The object distance is:

(a) 50 cm (b) 25 cm (c) 16.7 cm (d) 33.3 cm

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Correct Answer: (a) 50 cm

Explanation:
1/v - 1/u = 1/f → 1/50 - 1/u = 1/25 → u = -50 cm

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

(a) 880 V (b) 55 V (c) 220 V (d) 110 V

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Correct Answer: (b) 55 V

Explanation:
V_s = V_p × (N_s/N_p) = 220 × (1/4) = 55 V

8. The moderator in a nuclear reactor slows down:

(a) Neutrons (b) Protons (c) Electrons (d) Alpha particles

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Correct Answer: (a) Neutrons

Explanation:
Moderator slows down fast neutrons to thermal neutrons

9. If the length of a simple pendulum is decreased by 4%, the percentage change in time period is:

(a) 2% decrease (b) 4% decrease (c) 2% increase (d) No change

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Correct Answer: (a) 2% decrease

Explanation:
T ∝ √L → 4% decrease in L → 2% decrease in T

10. The SI unit of magnetic permeability (μ₀) is:

(a) H/m (b) N A⁻² (c) Both (a) and (b) (d) Wb/m

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

Explanation:
μ₀ = 4π × 10⁻⁷ H/m = N A⁻²