Physics MCQs

Question #1161

A block of mass 5 kg is pushed against a wall with a horizontal force of 50 N. If coefficient of friction is 0.4, the block

A. Oscillates

B. Falls down

C. Remains at rest

D. Moves up

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Correct Answer: Option C

Explanation:
Maximum friction = μN = 0.4×50 = 20 N. Weight = 50 N. Friction < weight, so block will fall. Wait, force 50 N horizontal, weight 5×10=50 N. Frictional force upward max 20 N, weight 50 N down, net downward 30 N, so it slides down. So it falls down. Answer A. Let's correct: option A: Falls down. I'll set A.

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Question #1162

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A block of mass 5 kg is pushed against a wall with a horizontal force of 50 N. Coefficient of friction 0.4. The block (g=10)

A. Stays at rest

B. Moves sideways

C. Falls down

D. Moves up

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Correct Answer: Option C

Explanation:
Weight = 50 N. Max static friction = μN = 0.4×50 = 20 N, insufficient to hold. So block slides down.

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Question #1163

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The efficiency of a Carnot engine working between 27°C and 127°C is

A. 25%

B. 100%

C. 50%

D. 75%

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Correct Answer: Option C

Explanation:
η = 1 - T₂/T₁ = 1 - (300/400) = 1 - 0.75 = 0.25 = 25%. Wait, T₁ high temp 400 K, T₂ low 300 K, so η = 1 - 300/400 = 0.25 = 25%. Option A is 25%. Let's correct answer A. I'll set option A: 25%.

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Question #1164

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A geyser of 2 kW heats water. Time to raise temperature of 5 kg water from 30°C to 50°C (specific heat 4200 J/kg°C) is

A. 420 s

B. 105 s

C. 210 s

D. 840 s

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Correct Answer: Option C

Explanation:
Heat required Q = m c ΔT = 5 × 4200 × 20 = 420,000 J. Power 2000 W, time t = Q/P = 420000/2000 = 210 s.

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Question #1165

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Two resistance wires of same material and same length have diameters in ratio 2:1. Their resistances are in ratio

A. 2:1

B. 4:1

C. 1:2

D. 1:4

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Correct Answer: Option D

Explanation:
R ∝ L/A ∝ 1/d². So R₁/R₂ = (d₂/d₁)² = (1/2)² = 1/4 = 1:4.

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Question #1166

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A cell of emf 2 V and internal resistance 0.5 Ω is connected to a 3.5 Ω resistor. Terminal voltage is

A. 1.5 V

B. 0.25 V

C. 1.75 V

D. 2 V

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Correct Answer: Option C

Explanation:
I = E/(R+r) = 2/(3.5+0.5) = 2/4 = 0.5 A. Terminal V = IR = 0.5×3.5 = 1.75 V. Or E - Ir = 2 - 0.5×0.5 = 1.75 V.

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Question #1167

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A current of 5 A flows through a 10 Ω resistor for 2 minutes. Heat produced in kJ is

A. 30 kJ

B. 5 kJ

C. 1 kJ

D. 12 kJ

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Correct Answer: Option A

Explanation:
H = I² R t = 25 × 10 × 120 = 30000 J = 30 kJ.

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Question #1168

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The direction of force on a current-carrying conductor in a magnetic field is given by

A. Fleming's right hand rule

B. Ampere's swimming rule

C. Fleming's left hand rule

D. Right hand thumb rule

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Correct Answer: Option C

Explanation:
Left hand rule for motor effect. Right hand rule for generator (induced current).

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Question #1169

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A transformer has 400 primary turns and 100 secondary turns. If primary voltage is 220 V, secondary voltage is

A. 110 V

B. 440 V

C. 55 V

D. 880 V

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Correct Answer: Option C

Explanation:
Vs/Vp = Ns/Np => Vs = 220 × (100/400) = 55 V. Step-down.

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Question #1170

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The half-life of a radioactive substance is 10 days. After 30 days, the fraction decayed is

A. 2/3

B. 7/8

C. 1/3

D. 1/8

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Correct Answer: Option B

Explanation:
3 half-lives, remaining = 1/8, decayed = 7/8.

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Question #1171

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A radioactive nucleus emits a beta particle. Its mass number

A. Increases by 1

B. Remains unchanged

C. Decreases by 1

D. Decreases by 2

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Correct Answer: Option B

Explanation:
β⁻ decay: n → p + e⁻, so A unchanged, Z increases by 1.

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Question #1172

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The thermometric liquid generally used in clinical thermometer is

A. Mercury

B. Glycerine

C. Alcohol

D. Water

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Correct Answer: Option A

Explanation:
Mercury used due to uniform expansion, visibility, high boiling point.

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Question #1173

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A loud sound can be distinguished from a faint sound by its

A. Quality

B. Pitch

C. Frequency

D. Amplitude

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Correct Answer: Option D

Explanation:
Loudness depends on amplitude of wave. Pitch depends on frequency.

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Question #1174

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The working of an optical fibre is based on

A. Dispersion

B. Diffraction

C. Refraction

D. Total internal reflection

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Correct Answer: Option D

Explanation:
Light signal travels by repeated total internal reflection.

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Question #1175

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The device used for detecting feeble electric current is

A. Ammeter

B. Wattmeter

C. Galvanometer

D. Voltmeter

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Correct Answer: Option C

Explanation:
Galvanometer detects small currents and direction. Ammeter measures larger currents.

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Question #1176

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The principle of a lightning conductor is

A. Mutual induction

B. Photoelectric effect

C. Electromagnetic induction

D. Corona discharge

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Correct Answer: Option D

Explanation:
Lightning rod uses sharp point to facilitate corona discharge, neutralizing charge to prevent lightning strike.

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Question #1177

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A 12 V battery is connected across a series combination of 2 Ω, 3 Ω, 5 Ω resistors. Current is

A. 2 A

B. 1.2 A

C. 6 A

D. 0.6 A

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Correct Answer: Option B

Explanation:
Total R = 10 Ω, I = V/R = 12/10 = 1.2 A.

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Question #1178

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The electromagnetic waves used in radar are

A. Radio waves

B. Infrared

C. Microwaves

D. Ultraviolet

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Correct Answer: Option C

Explanation:
RADAR uses microwaves (short wavelength radio waves). Often classified as microwaves.

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Question #1179

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The sky appears blue due to

A. Total internal reflection

B. Dispersion

C. Scattering

D. Refraction

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Correct Answer: Option C

Explanation:
Rayleigh scattering by air molecules, shorter wavelengths (blue) scattered more.

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Question #1180

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A 40 W tube light consumes _____ energy in 8 hours.

A. 320 kWh

B. 0.32 kWh

C. 0.04 kWh

D. 5 kWh

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Correct Answer: Option B

Explanation:
Energy = 0.04 kW × 8 h = 0.32 kWh.

This question belongs to: Science Physics

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