Physics MCQs

Question #861

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The radius of curvature of a convex mirror of focal length 20 cm is

A. 20 cm

B. 30 cm

C. 40 cm

D. 10 cm

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Correct Answer: Option C

Explanation:
R = 2f = 40 cm. For convex, f positive, R positive.

This question belongs to: Science Physics

Question #862

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An object placed at infinity in front of a convex mirror forms image at

A. At infinity

B. C behind mirror

C. F behind mirror

D. Between P and F behind mirror

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Correct Answer: Option C

Explanation:
Distant object image at focus, behind mirror, virtual, diminished.

This question belongs to: Science Physics

Question #863

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The unit of specific heat capacity is

A. J

B. J/kg°C

C. J/°C

D. J/kg

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Correct Answer: Option B

Explanation:
Q = m c ΔT => c = Q/(m ΔT), unit J/(kg °C).

This question belongs to: Science Physics

Question #864

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Which of the following is a non-ohmic conductor?

A. Copper wire

B. Silver wire

C. Diode

D. Iron wire

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Correct Answer: Option C

Explanation:
Diode has non-linear I-V characteristic. Metals are ohmic.

This question belongs to: Science Physics

Question #865

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The time of flight of a projectile is maximum when angle of projection is

A. 90°

B. 30°

C. 60°

D. 45°

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Correct Answer: Option A

Explanation:
T = 2u sinθ/g, max when sinθ=1 => θ=90° (vertical).

This question belongs to: Science Physics

Question #866

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A body of mass 5 kg moving with velocity 2 m/s collides with a stationary body of mass 3 kg and sticks to it. Combined velocity is

A. 1.25 m/s

B. 2 m/s

C. 0.8 m/s

D. 5 m/s

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Correct Answer: Option A

Explanation:
Momentum before = 5×2=10, after = (5+3)v => v=10/8=1.25 m/s.

This question belongs to: Science Physics

Question #867

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The unit of electric power can be expressed as

A. Coulomb × volt

B. Ohm × meter

C. Volt × ampere

D. Joule × second

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Correct Answer: Option C

Explanation:
P = V I, so watt = volt × ampere.

This question belongs to: Science Physics

Question #868

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The primary colours of light are

A. Red, orange, violet

B. Red, yellow, blue

C. Red, green, blue

D. Cyan, magenta, yellow

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Correct Answer: Option C

Explanation:
Additive primary: RGB.

This question belongs to: Science Physics

Question #869

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A radioactive nucleus emits a beta particle. Its atomic number

A. Increases by 1

B. Remains same

C. Decreases by 1

D. Decreases by 2

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Correct Answer: Option A

Explanation:
β⁻ decay: neutron → proton + electron, Z increases by 1.

This question belongs to: Science Physics

Question #870

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The device used to measure the emf of a cell without drawing current is

A. Potentiometer

B. Ammeter

C. Voltmeter

D. Galvanometer

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Correct Answer: Option A

Explanation:
Potentiometer: null deflection method, no current drawn from cell.

This question belongs to: Science Physics

Question #871

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A convex lens is immersed in a liquid of same refractive index. Its focal length becomes

A. Same

B. Zero

C. Infinite

D. Half

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Correct Answer: Option C

Explanation:
Relative refractive index = 1, so lens behaves like glass slab, f infinite.

This question belongs to: Science Physics

Question #872

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The time period of a satellite in geostationary orbit is

A. 12 hours

B. 24 hours

C. 1 month

D. 365 days

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Correct Answer: Option B

Explanation:
Geostationary orbit period equals Earth's rotation period, 24 hours.

This question belongs to: Science Physics

Question #873

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The substance used as moderator in nuclear reactor must

A. Absorb neutrons

B. Increase neutron energy

C. Slow down neutrons without absorbing them

D. Cool the reactor

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Correct Answer: Option C

Explanation:
Moderator slows neutrons via elastic collisions, low absorption. Heavy water, graphite.

This question belongs to: Science Physics

Question #874

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A body of mass m is taken from Earth's surface to a height equal to twice Earth's radius. Change in potential energy is

A. mgR

B. 2mgR/3

C. 3mgR

D. mgR/3

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Correct Answer: Option B

Explanation:
ΔU = GMm (1/R - 1/(R+2R)) = GMm (1/R - 1/3R) = (2/3)GMm/R = (2/3)mgR.

This question belongs to: Science Physics

Question #875

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Which of the following is not an electromagnetic wave?

A. Sound waves

B. Gamma rays

C. Ultraviolet

D. X-rays

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Correct Answer: Option A

Explanation:
Sound waves are mechanical, require medium.

This question belongs to: Science Physics

Question #876

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The material of a permanent magnet should have

A. High retentivity, low coercivity

B. Low retentivity, low coercivity

C. Low retentivity, high coercivity

D. High retentivity, high coercivity

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Correct Answer: Option D

Explanation:
Permanent magnets need high retentivity and high coercivity to stay magnetized. Steel, alnico.

This question belongs to: Science Physics

Question #877

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A photon of energy 3.3 eV has frequency approximately (h=4.14×10⁻¹⁵ eV s)

A. 1.25×10¹⁵ Hz

B. 3×10⁸ Hz

C. 8×10¹⁴ Hz

D. 5×10¹⁴ Hz

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Correct Answer: Option C

Explanation:
f = E/h = 3.3 / 4.14×10⁻¹⁵ ≈ 8×10¹⁴ Hz.

This question belongs to: Science Physics

Question #878

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The dimensional formula of strain is

A. [MLT⁻²]

B. [T⁻¹]

C. [L]

D. [M⁰L⁰T⁰]

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Correct Answer: Option D

Explanation:
Strain = ΔL/L, dimensionless, so [M⁰L⁰T⁰].

This question belongs to: Science Physics

Question #879

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A boy throws a ball vertically upward with velocity 20 m/s. Time after which ball returns to his hands (g=10) is

A. 8 s

B. 1 s

C. 4 s

D. 2 s

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Correct Answer: Option C

Explanation:
Total time = 2u/g = 40/10 = 4 s.

This question belongs to: Science Physics

Question #880

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The product of force and time is called

A. Energy

B. Impulse

C. Work

D. Power

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Correct Answer: Option B

Explanation:
Impulse = F Δt.

This question belongs to: Science Physics

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