Physics MCQ Practice 28 — Science Foundation Course for Class 11 & 12

1. A body is projected horizontally with velocity 20 m/s from a height of 45 m. The time of flight (g=10 m/s ²) is:

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

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Correct Answer: (a) 3 s

Explanation:
t = √(2h/g) = √(90/10) = 3 s

2. The escape velocity on Earth is 11.2 km/s. On a planet with same density but half radius, the escape velocity is:

(a) 11.2 km/s (b) 5.6 km/s (c) 22.4 km/s (d) 7.92 km/s

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Correct Answer: (b) 5.6 km/s

Explanation:
v_esc ∝ R (same density) → half radius → half escape velocity

3. The equivalent resistance when 2 Ω, 3 Ω and 6 Ω are connected in series is:

(a) 11 Ω (b) 1 Ω (c) 6 Ω (d) 2 Ω

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Correct Answer: (a) 11 Ω

Explanation:
R = 2 + 3 + 6 = 11 Ω

4. The velocity of sound in air at 0°C is 332 m/s. At 30°C it is approximately:

(a) 332 m/s (b) 350 m/s (c) 364 m/s (d) 300 m/s

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Correct Answer: (b) 350 m/s

Explanation:
v ∝ √T → √(303/273) × 332 ≈ 350 m/s

5. The magnetic field at a point inside a long straight wire carrying current I at distance r from axis is:

(a) μ₀I r / (2π R²) (b) μ₀I / (2πr) (c) μ₀I / (2r) (d) Zero

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Correct Answer: (a) μ₀I r / (2π R²)

Explanation:
B inside wire = (μ₀ I r) / (2π R²)

6. A convex lens of focal length 25 cm forms a real image at 75 cm. The object distance is:

(a) 37.5 cm (b) 18.75 cm (c) 50 cm (d) 15 cm

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Correct Answer: (a) 37.5 cm

Explanation:
1/v - 1/u = 1/f → u = -37.5 cm

7. The impedance of a series LCR circuit is minimum at:

(a) Low frequency (b) High frequency (c) Resonance frequency (d) Zero frequency

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Correct Answer: (c) Resonance frequency

Explanation:
Z is minimum (=R) at resonance

8. The moderator used in CANDU reactor is:

(a) Graphite (b) Heavy water (c) Ordinary water (d) Liquid sodium

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Correct Answer: (b) Heavy water

Explanation:
CANDU reactors use heavy water as moderator and coolant

9. If the length of a simple pendulum is decreased by 36%, the percentage change in time period is:

(a) 18% decrease (b) 36% decrease (c) 20% decrease (d) 9% decrease

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Correct Answer: (a) 18% decrease

Explanation:
T ∝ √L → 36% decrease in L → 18% decrease in T

10. The SI unit of capacitance is:

(a) Farad (b) Henry (c) Ohm (d) Weber

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Correct Answer: (a) Farad

Explanation:
Capacitance C is measured in Farad (F)