Physics MCQs

Question #761

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The phenomenon of persistence of hearing is used in

A. Echo

B. Sonar

C. Stethoscope

D. Reverberation

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Correct Answer: Option D

Explanation:
Reverberation: repeated reflections blending, due to persistence (0.1 s).

This question belongs to: Science Physics

Question #762

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The frequency of infrasound is

A. Above 20 kHz

B. Below 20 Hz

C. 20 Hz - 20 kHz

D. Below 10 Hz

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Correct Answer: Option B

Explanation:
Infrasound < 20 Hz, ultrasound > 20 kHz.

This question belongs to: Science Physics

Question #763

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A concave mirror forms a real, inverted, magnified image when object is

A. Between F and C

B. At infinity

C. At C

D. Between P and F

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Correct Answer: Option A

Explanation:
Between F and C: image beyond C, magnified, inverted, real.

This question belongs to: Science Physics

Question #764

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A lens which is thicker at center and thinner at edges is

A. Plano-concave

B. Cylindrical

C. Concave

D. Convex

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Correct Answer: Option D

Explanation:
Convex lens converges light, thicker centre.

This question belongs to: Science Physics

Question #765

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A person with myopia uses spectacles of power -2 D. Far point without glasses is

A. 25 cm

B. 2 m

C. 50 cm

D. Infinity

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Correct Answer: Option C

Explanation:
For myopia, corrective lens forms image of distant object at far point. 1/f = 1/(-far point) - 1/(-∞) => -2 = -1/F => F = 0.5 m = 50 cm.

This question belongs to: Science Physics

Question #766

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A ray of light travels from glass (μ=1.5) to air. Critical angle is

A. sin⁻¹(1.5)

B. sin⁻¹(1/3)

C. sin⁻¹(1/1.5)

D. sin⁻¹(2/3)

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Correct Answer: Option C

Explanation:
sin C = 1/μ = 2/3 ≈ 0.6667, C = sin⁻¹(2/3). So option A: sin⁻¹(2/3). Wait sin C = n2/n1 = 1/1.5 = 2/3. So C = sin⁻¹(2/3). Option A is sin⁻¹(2/3). I'll correct to A.

This question belongs to: Science Physics

Question #767

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Which color of light is scattered most by atmosphere?

A. Yellow

B. Green

C. Blue

D. Red

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Correct Answer: Option C

Explanation:
Rayleigh scattering ∝ 1/λ⁴. Blue has shorter wavelength, scattered more. Sky appears blue.

This question belongs to: Science Physics

Question #768

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The unit of electric current in CGS system is

A. Coulomb

B. Abcoulomb

C. Ampere

D. Statampere

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Correct Answer: Option D

Explanation:
CGS electrostatic unit of current is statampere. EMU is abampere. SI is ampere.

This question belongs to: Science Physics

Question #769

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A wire of resistivity ρ, length L, area A has resistance R. If length doubled and area halved, new resistance is

A. 4R

B. 2R

C. R/2

D. R

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Correct Answer: Option A

Explanation:
R = ρL/A. New R' = ρ(2L)/(A/2) = 4ρL/A = 4R.

This question belongs to: Science Physics

Question #770

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The heating element of a heater is made of nichrome because it has

A. High resistivity, low melting point

B. Low resistivity, low melting point

C. High resistivity, high melting point

D. Low resistivity, high melting point

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Correct Answer: Option C

Explanation:
Nichrome high resistivity generates more heat, high melting point avoids melting at high temperature.

This question belongs to: Science Physics

Question #771

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The commercial unit of electrical energy is

A. Watt

B. Kilowatt-hour

C. Volt-ampere

D. Joule

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Correct Answer: Option B

Explanation:
kWh used for billing.

This question belongs to: Science Physics

Question #772

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Two resistors in series have equivalent 6 Ω, in parallel 4/3 Ω. Individual resistors are

A. 3 Ω and 3 Ω

B. 2 Ω and 4 Ω

C. 2 Ω and 2 Ω

D. 1 Ω and 5 Ω

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Correct Answer: Option B

Explanation:
Series: R1+R2=6. Parallel: (R1×R2)/(6)=4/3 => R1R2=8. Solving: R1,R2 = 2,4.

This question belongs to: Science Physics

Question #773

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An electromagnet is made by

A. Copper core

B. Steel core

C. Soft iron core

D. Air core

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Correct Answer: Option C

Explanation:
Soft iron has high permeability, low retentivity, easily magnetized and demagnetized.

This question belongs to: Science Physics

Question #774

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Fleming's left hand rule gives direction of

A. Magnetic field due to current

B. Induced current

C. Force on current-carrying conductor in magnetic field

D. Induced emf

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Correct Answer: Option C

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

This question belongs to: Science Physics

Question #775

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Which of the following is an application of electromagnetic induction?

A. Moving coil galvanometer

B. Dynamo

C. Electric fuse

D. Electric bell

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Correct Answer: Option B

Explanation:
Dynamo/generator converts mechanical to electrical energy using induction.

This question belongs to: Science Physics

Question #776

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The energy of electron in ground state of hydrogen is -13.6 eV. Ionization energy is

A. 13.6 eV

B. 0 eV

C. 27.2 eV

D. 3.4 eV

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Correct Answer: Option A

Explanation:
Ionization energy is energy to remove electron from ground state to infinity, 13.6 eV.

This question belongs to: Science Physics

Question #777

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The number of neutrons in ²³⁸₉₂U is

A. 330

B. 238

C. 146

D. 92

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Correct Answer: Option C

Explanation:
Neutrons = A - Z = 238 - 92 = 146.

This question belongs to: Science Physics

Question #778

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Which is the most penetrating radiation?

A. X-rays

B. Alpha

C. Beta

D. Gamma

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Correct Answer: Option D

Explanation:
Gamma rays highest penetration, alpha least.

This question belongs to: Science Physics

Question #779

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In a nuclear reactor, heavy water is used as

A. Control rod

B. Coolant

C. Moderator

D. Fuel

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Correct Answer: Option C

Explanation:
Heavy water (D₂O) slows neutrons, good moderator.

This question belongs to: Science Physics

Question #780

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A pendulum has time period 2 s. If its length is increased by 4 times, new period is

A. 2 s

B. 8 s

C. 1 s

D. 4 s

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Correct Answer: Option D

Explanation:
T ∝ √L, L'=4L => T' = √4 T = 2×2 = 4 s.

This question belongs to: Science Physics

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