Physics MCQs

Question #401

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The change in momentum of a body is equal to

A. Force

B. Impulse

C. Energy

D. Work

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Correct Answer: Option B

Explanation:
Impulse = F Δt = Δp (change in momentum). Derived from Newton's second law. Force is rate of change of momentum. Impulse-momentum theorem important for collisions.

This question belongs to: Science Physics

Question #402

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A wire of resistance 9 Ω is bent to form an equilateral triangle. The resistance across any two vertices is

A. 9 Ω

B. 3 Ω

C. 2 Ω

D. 6 Ω

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Correct Answer: Option C

Explanation:
Total 9 Ω, each side 3 Ω. Across two vertices, one side is 3 Ω in parallel with series of two sides (3+3=6 Ω). Equivalent: (3×6)/(3+6) = 18/9 = 2 Ω. Triangle resistance network.

This question belongs to: Science Physics

Question #403

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Which of the following is a good conductor of electricity?

A. Glass

B. Copper

C. Rubber

D. Wood

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Correct Answer: Option B

Explanation:
Copper has free electrons, very low resistivity, excellent conductor. Glass, rubber, wood are insulators. Silver best conductor, but copper widely used. Graphite conducts but non-metal.

This question belongs to: Science Physics

Question #404

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The focal length of a concave mirror is 15 cm. The radius of curvature is

A. 45 cm

B. 15 cm

C. 30 cm

D. 7.5 cm

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Correct Answer: Option C

Explanation:
For spherical mirrors, R = 2f. So R = 2 × 15 = 30 cm. Sign convention: for concave mirror, f and R are negative by Cartesian convention, but magnitude 30 cm. So 30 cm is correct.

This question belongs to: Science Physics

Question #405

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A cyclist moving at 18 km/h stops pedalling and comes to rest after 10 m due to friction. Deceleration is

A. 1.25 m/s²

B. 5 m/s²

C. 0.8 m/s²

D. 2.5 m/s²

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Correct Answer: Option A

Explanation:
18 km/h = 5 m/s. v² = u² + 2as => 0 = 5² + 2a×10 => 25 + 20a = 0 => a = -25/20 = -1.25 m/s², deceleration = 1.25 m/s². Negative acceleration.

This question belongs to: Science Physics

Question #406

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The boiling point of water on Kelvin scale is

A. 100 K

B. 273.15 K

C. 373.15 K

D. 0 K

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Correct Answer: Option C

Explanation:
Boiling point of water = 100°C = 100 + 273.15 = 373.15 K. Melting point of ice 0°C = 273.15 K. Kelvin is SI unit, no degree symbol.

This question belongs to: Science Physics

Question #407

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The layer of atmosphere that reflects radio waves is

A. Ionosphere

B. Stratosphere

C. Troposphere

D. Mesosphere

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Correct Answer: Option A

Explanation:
Ionosphere contains ions and free electrons, reflects radio waves back to Earth, enabling long-distance radio communication. Used in skywave propagation. Troposphere weather layer.

This question belongs to: Science Physics

Question #408

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An object is placed at the centre of curvature of a concave mirror. The image formed is

A. Real, inverted, diminished

B. Virtual, inverted, same size

C. Real, inverted, same size

D. Virtual, erect, magnified

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Correct Answer: Option C

Explanation:
At C (centre of curvature), image is at C, real, inverted, same size. At F, image at infinity. Beyond C, between F and C, diminished. Object between F and C gives beyond C, enlarged.

This question belongs to: Science Physics

Question #409

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The property of a body to resist change in its state of motion is called

A. Inertia

B. Force

C. Weight

D. Momentum

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Correct Answer: Option A

Explanation:
Inertia is directly proportional to mass. Heavier object harder to accelerate/decelerate. Newton's first law defines inertia. Momentum is mass × velocity, depends on motion.

This question belongs to: Science Physics

Question #410

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The unit of power is

A. Pascal

B. Joule

C. Newton

D. Watt

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Correct Answer: Option D

Explanation:
Watt (W) = Joule/second. SI unit of power. Horsepower is another unit (1 HP ≈ 746 W). Joule is energy, Newton force, Pascal pressure.

This question belongs to: Science Physics

Question #411

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A 10 Ω resistor is connected across a 5 V battery. The current flowing is

A. 5 A

B. 50 A

C. 0.5 A

D. 2 A

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Correct Answer: Option C

Explanation:
I = V/R = 5/10 = 0.5 A. Ohm's law. Simple calculation. Power P = V×I = 2.5 W.

This question belongs to: Science Physics

Question #412

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The number of protons in an atom determines its

A. Isotope

B. Mass number

C. Atomic number

D. Neutron number

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Correct Answer: Option C

Explanation:
Atomic number Z = number of protons. Defines chemical element. Mass number = protons + neutrons. Isotopes same Z, different neutrons. Isobars same A, different Z.

This question belongs to: Science Physics

Question #413

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The colour of light that deviates least in a glass prism is

A. Green

B. Violet

C. Blue

D. Red

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Correct Answer: Option D

Explanation:
Dispersion: red has longest wavelength, lowest refractive index, deviates least. Violet deviates most. So spectrum: red at top (least deviation), violet at bottom.

This question belongs to: Science Physics

Question #414

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Which of the following uses the principle of electromagnetic induction?

A. Electric heater

B. Transformer

C. Fuse

D. Incandescent bulb

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Correct Answer: Option B

Explanation:
Transformer, induction cooker, generator use induction. Heater and bulb use heating effect of current. Fuse melts by heat. Induction: changing magnetic field induces current.

This question belongs to: Science Physics

Question #415

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The unit of latent heat is

A. J

B. W

C. J/kg

D. J/°C

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Correct Answer: Option C

Explanation:
Latent heat per unit mass, so Q = mL, L = Q/m, unit J/kg (or cal/g). Specific latent heat of fusion/vaporization. Heat required for phase change without temperature change.

This question belongs to: Science Physics

Question #416

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The phenomenon of bouncing back of light from a surface is called

A. Dispersion

B. Reflection

C. Refraction

D. Diffraction

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Correct Answer: Option B

Explanation:
Reflection: light returns into same medium. Laws: angle i = angle r. Refraction is bending into another medium. Dispersion splitting colours. Diffraction spreading around obstacles.

This question belongs to: Science Physics

Question #417

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A body of mass 2 kg is moving with velocity 5 m/s. Its kinetic energy is

A. 5 J

B. 50 J

C. 10 J

D. 25 J

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Correct Answer: Option D

Explanation:
K.E. = ½ m v² = ½ × 2 × 5² = 1 × 25 = 25 J. Use formula correctly. If velocity doubled, KE quadrupled. Unit joule.

This question belongs to: Science Physics

Question #418

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The number of significant figures in 3.00 × 10⁸ is

A. 1

B. 2

C. 3

D. 8

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Correct Answer: Option C

Explanation:
Scientific notation: 3.00 has three significant figures (3,0,0). Exponent part not counted. It's a clear way to show precision. 3×10⁸ has 1, 3.0×10⁸ has 2.

This question belongs to: Science Physics

Question #419

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The ratio of SI to CGS unit of force is

A. 10⁵

B. 10³

C. 10²

D. 10⁷

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Correct Answer: Option A

Explanation:
SI unit Newton (kg m/s²), CGS unit dyne (g cm/s²). 1 N = 10⁵ dyne. Conversion: 1 kg = 10³ g, 1 m = 100 cm, so 1 N = 10³ × 10² = 10⁵ dyne. Ratio N/dyne = 10⁵.

This question belongs to: Science Physics

Question #420

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The device which converts AC to DC is called

A. Inverter

B. Transformer

C. Oscillator

D. Rectifier

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Correct Answer: Option D

Explanation:
Rectifier (diode bridge) converts AC to DC. Inverter DC to AC. Transformer changes AC voltage level. Oscillator generates AC signal. Electronic devices often need DC.

This question belongs to: Science Physics

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