Physics MCQs

Question #581

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Beta rays consist of:

A. Helium nuclei

B. Electromagnetic waves

C. Neutrons

D. High-speed electrons

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Correct Answer: Option D

Explanation:
Beta (β) rays are streams of high-speed electrons (β⁻) or positrons (β⁺) emitted during radioactive decay. Beta-minus decay: neutron → proton + electron + antineutrino. Alpha rays are helium nuclei (²He⁴); gamma rays are high-energy photons; neutrons are neutral particles. Memory tip: 'Beta = electrons; Alpha = He nucleus; Gamma = photons'. This classification question tests knowledge of radioactivity types, crucial for modern physics in competitive exams. Always distinguish penetration power: alpha < beta < gamma.

This question belongs to: Science Physics

Question #582

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Nuclear fission involves:

A. Combining light nuclei

B. Capture of orbital electrons

C. Splitting heavy nuclei

D. Emission of electrons from nucleus

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Correct Answer: Option C

Explanation:
Nuclear fission is the splitting of a heavy nucleus (e.g., uranium-235, plutonium-239) into lighter nuclei, releasing energy and neutrons. This process powers nuclear reactors and atomic bombs. Fusion combines light nuclei (e.g., hydrogen to helium), powering stars. Memory aid: 'Fission = splitting heavy; Fusion = joining light'. This conceptual question tests understanding of nuclear reactions, frequently examined in competitive exams. Always link fission to chain reactions (neutrons induce further fissions) and critical mass concepts.

This question belongs to: Science Physics

Question #583

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

A. 1/8

B. 1/2

C. 1/16

D. 1/3

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Correct Answer: Option A

Explanation:
Number of half-lives n = total time / half-life = 30 days / 10 days = 3. Fraction remaining = (1/2)ⁿ = (1/2)³ = 1/8. This exponential decay law is fundamental in radioactivity. Memory tip: 'After n half-lives, fraction = 1/2ⁿ'. Competitive exams frequently test such calculations with varying time intervals. Always compute number of half-lives first. Note: Activity (decays per second) also reduces by same fraction. This problem assesses understanding of half-life concept beyond rote memorization.

This question belongs to: Science Physics

Question #584

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In a nuclear reactor, control rods are made of materials that:

A. Reflect neutrons

B. Absorb neutrons

C. Moderate neutrons

D. Emit neutrons

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Correct Answer: Option B

Explanation:
Control rods (made of cadmium, boron, or hafnium) absorb neutrons to regulate the fission chain reaction rate. Inserting rods deeper reduces neutron population, slowing reaction; withdrawing them increases reaction rate. Moderators (water, graphite) slow neutrons to thermal energies for efficient fission. Memory aid: 'Control rods = neutron absorbers; Moderators = neutron slowers'. This application question tests knowledge of reactor components, common in competitive exams. Always distinguish roles: fuel (fissionable material), moderator, control rods, coolant.

This question belongs to: Science Physics

Question #585

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A wave has frequency 50 Hz and wavelength 2 m. Its speed is:

A. 100 m/s

B. 25 m/s

C. 200 m/s

D. 50 m/s

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Correct Answer: Option A

Explanation:
Wave speed v = frequency (f) × wavelength (λ). Thus v = 50 Hz × 2 m = 100 m/s. This fundamental wave equation applies to all periodic waves (sound, light, water). Memory aid: 'v = fλ – the universal wave equation'. Competitive exams frequently test this direct calculation. Always ensure units: Hz = s⁻¹, so (s⁻¹)×m = m/s, correct for speed. This problem assesses basic wave property understanding, crucial for sound and light topics.

This question belongs to: Science Physics

Question #586

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Simple harmonic motion is characterized by:

A. Constant velocity

B. Constant acceleration

C. Acceleration proportional to velocity

D. Acceleration proportional to displacement and directed opposite

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Correct Answer: Option D

Explanation:
SHM definition: acceleration a ∝ -x (displacement), i.e., a = -ω²x. This restoring acceleration causes oscillatory motion. Constant acceleration implies uniformly accelerated motion (not oscillatory). Constant velocity implies no acceleration. Memory tip: 'SHM: a = -ω²x; force F = -kx (Hooke's law)'. This conceptual question tests fundamental SHM characteristics, frequently examined in competitive exams. Always link to examples: mass-spring system, simple pendulum (small angles), LC circuits.

This question belongs to: Science Physics

Question #587

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A lactometer is used to:

A. Measure liquid density

B. Measure milk purity

C. Measure wind speed

D. Measure humidity

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Correct Answer: Option B

Explanation:
Lactometer is a specialized hydrometer for measuring milk purity/density. It works on Archimedes' principle: pure milk has specific density; adulteration (with water) changes density, altering lactometer reading. While it measures density, its specific application is milk testing. Option B is partially correct but not specific; competitive exams expect the precise application. Memory tip: 'Lacto = milk; meter = measure'. This application-based question tests knowledge of scientific instruments in daily life, frequently appearing in competitive exams. Always note context-specific uses of general instruments.

This question belongs to: Science Physics

Question #588

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The instrument that converts mechanical energy into electrical energy is:

A. Transformer

B. Generator

C. Electric motor

D. Galvanometer

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Correct Answer: Option B

Explanation:
Generator converts mechanical energy (rotation) to electrical energy via electromagnetic induction. Motor does the reverse (electrical to mechanical). Transformer changes AC voltage levels; galvanometer detects small currents. Memory aid: 'Generator: motion ⇒ electricity; Motor: electricity ⇒ motion'. This principle-based question tests understanding of energy conversion devices, crucial for electromagnetism in competitive exams. Always link device function to underlying physics law: generator (Faraday's law), motor (Lorentz force).

This question belongs to: Science Physics

Question #589

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A seismograph is used to detect:

A. Earthquakes

B. Magnetic field variations

C. Atmospheric pressure changes

D. Sound waves in water

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Correct Answer: Option A

Explanation:
Seismograph detects and records ground motions caused by earthquakes, volcanic activity, or explosions. It measures seismic waves (P-waves, S-waves). Barometer detects pressure changes; hydrophone detects underwater sound; magnetometer detects magnetic fields. Memory tip: 'Seismo = earthquake (like seismology)'. This instrument-application question tests knowledge of geophysical tools, frequently examined in competitive exams. Always associate instrument names with their field of use: seismograph (geology), barometer (meteorology), etc.

This question belongs to: Science Physics

Question #590

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The working principle of LED is based on:

A. Electroluminescence

B. Fluorescence

C. Incandescence

D. Heating effect of current

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Correct Answer: Option A

Explanation:
LED (Light Emitting Diode) works on electroluminescence: when electrons recombine with holes in a semiconductor junction, energy is released as photons. This is distinct from incandescence (heating filament, like bulbs), fluorescence (absorb UV, emit visible), or heating effect. Memory aid: 'LED = semiconductor light emission; no filament'. This modern application question tests knowledge of everyday physics, common in competitive exams. Always link device to underlying phenomenon: LED (electroluminescence), laser (stimulated emission), solar cell (photovoltaic effect).

This question belongs to: Science Physics

Question #591

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In a pressure cooker, food cooks faster because:

A. Boiling point of water increases due to high pressure

B. Material conducts heat better

C. Steam circulates rapidly

D. Heat is trapped inside

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Correct Answer: Option A

Explanation:
Pressure cooker seals steam, increasing internal pressure above atmospheric. Higher pressure raises water's boiling point (above 100°C), allowing food to cook at higher temperature, speeding up chemical reactions. Option A is vague; C and D are secondary effects. Memory tip: 'Higher pressure ⇒ higher boiling point ⇒ faster cooking'. This daily-life physics question tests application of pressure-temperature relationship in liquids, frequently appearing in competitive exams. Always recall that phase change temperatures depend on pressure (e.g., water boils below 100°C on mountains).

This question belongs to: Science Physics

Question #592

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Solar cells convert:

A. Chemical energy to electrical energy

B. Light energy to electrical energy

C. Thermal energy to electrical energy

D. Electrical energy to light energy

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Correct Answer: Option B

Explanation:
Solar cells (photovoltaic cells) convert light energy (photons) directly into electrical energy via the photovoltaic effect: photons excite electrons in semiconductor material, creating electron-hole pairs that generate voltage. This is distinct from solar thermal (light to heat to electricity) or batteries (chemical to electrical). Memory aid: 'Photo = light; voltaic = electricity'. This renewable energy application question tests knowledge of energy conversion principles, common in competitive exams. Always distinguish photovoltaic (direct light-electricity) from other solar technologies.

This question belongs to: Science Physics

Question #593

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A fuse in an electrical circuit is designed to:

A. Store electrical energy

B. Protect against overcurrent by melting

C. Increase current flow

D. Convert AC to DC

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Correct Answer: Option B

Explanation:
Fuse is a safety device with a wire that melts when current exceeds rated value, breaking the circuit and preventing damage from overcurrent/short circuits. It operates on Joule heating (I²R). Option A is opposite; C describes capacitor; D describes rectifier. Memory tip: 'Fuse = sacrificial overcurrent protector'. This practical application question tests knowledge of electrical safety devices, frequently examined in competitive exams. Always link fuse rating to circuit requirements: fuse current rating slightly above normal operating current.

This question belongs to: Science Physics

Question #594

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The scientist who formulated the universal law of gravitation is:

A. Galileo Galilei

B. Johannes Kepler

C. Albert Einstein

D. Isaac Newton

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Correct Answer: Option D

Explanation:
Isaac Newton formulated the universal law of gravitation in his Principia Mathematica (1687), stating F = Gm₁m₂/r². Galileo studied falling bodies; Kepler derived planetary motion laws; Einstein developed general relativity (gravity as spacetime curvature). Memory aid: 'Newton = gravity apple story'. This history-based question tests knowledge of key scientific contributions, frequently appearing in competitive exams. Always associate scientists with their specific discoveries to avoid confusion between classical and modern physics pioneers.

This question belongs to: Science Physics

Question #595

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C. V. Raman is known for his work on:

A. Photoelectric effect

B. Electromagnetic induction

C. Raman effect (light scattering)

D. Theory of relativity

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Correct Answer: Option C

Explanation:
Sir C. V. Raman discovered the Raman effect in 1928: inelastic scattering of photons by molecules, changing wavelength, providing information about molecular structure. He received the Nobel Prize in Physics in 1930. Photoelectric effect: Einstein; relativity: Einstein; electromagnetic induction: Faraday. Memory tip: 'Raman = scattering of light'. This scientist-discovery question tests knowledge of Indian contributions to physics, commonly featured in competitive exams. Always link Nobel laureates to their specific awarded work.

This question belongs to: Science Physics

Question #596

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J. J. Thomson is credited with the discovery of:

A. Nucleus

B. Electron

C. Neutron

D. Proton

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Correct Answer: Option B

Explanation:
J. J. Thomson discovered the electron in 1897 through cathode ray tube experiments, measuring charge-to-mass ratio (e/m) of cathode rays. Proton: Rutherford; neutron: Chadwick; nucleus: Rutherford's gold foil experiment. Memory aid: 'Thomson = plum pudding model (electrons in positive sphere)'. This historical question tests knowledge of subatomic particle discoveries, frequently examined in competitive exams. Always recall the experimental methods: Thomson (cathode rays), Millikan (oil drop for e), Rutherford (alpha scattering).

This question belongs to: Science Physics

Question #597

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Assertion (A): The acceleration due to gravity is less at the equator than at the poles. Reason (R): Earth's rotation causes a centrifugal effect that reduces effective gravity at the equator.

A. A is true, but R is false

B. A is false, but R is true

C. Both A and R are true, and R is the correct explanation of A

D. Both A and R are true, but R is not the correct explanation of A

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Correct Answer: Option C

Explanation:
Assertion is true: g is about 9.78 m/s² at equator vs 9.83 m/s² at poles. Reason is true and correctly explains A: Earth's rotation creates centrifugal acceleration outward, maximum at equator (radius of rotation = Earth's radius), reducing effective g. Additionally, equatorial bulge increases distance from center, further reducing g. Memory tip: 'Rotation effect: g_effective = g - ω²R cos²φ'. This assertion-reason question tests nuanced understanding of gravity variation, common in competitive exams. Always verify both statements independently before assessing the explanatory link.

This question belongs to: Science Physics

Question #598

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Assertion (A): In a purely resistive AC circuit, voltage and current are in phase. Reason (R): Resistors do not store energy; they dissipate it as heat.

A. Both A and R are true, and R is the correct explanation of A

B. Both A and R are true, but R is not the correct explanation of A

C. A is true, but R is false

D. A is false, but R is true

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Correct Answer: Option A

Explanation:
Assertion is true: in resistive AC circuits, V and I reach peaks simultaneously (phase difference 0°). Reason is true and explains A: resistors obey Ohm's law instantaneously (V=IR), with no energy storage mechanism (unlike capacitors/inductors that cause phase shifts via energy storage/release). Thus, no phase difference arises. Memory aid: 'Resistors: V and I in phase; Capacitors: I leads V; Inductors: V leads I'. This assertion-reason question tests AC circuit fundamentals, frequently examined. Always link phase behavior to energy storage properties of components.

This question belongs to: Science Physics

Question #599

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A body is moving with uniform speed in a circular path. Which statement is correct?

A. Acceleration is zero

B. Velocity is constant

C. No force acts on the body

D. Acceleration is directed towards the center

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Correct Answer: Option D

Explanation:
In uniform circular motion, speed is constant but velocity direction changes continuously, requiring centripetal acceleration directed toward the center (a = v²/r). By Newton's second law, a centripetal force must act. Velocity isn't constant (direction changes); acceleration isn't zero; force is required. Memory tip: 'Uniform circular motion: constant speed, changing velocity, center-seeking acceleration'. This conceptual question tests understanding of circular dynamics, crucial for mechanics in competitive exams. Always distinguish speed (scalar) from velocity (vector) in motion analysis.

This question belongs to: Science Physics

Question #600

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The dimensional formula for energy density (energy per unit volume) is the same as that of:

A. Power

B. Momentum

C. Pressure

D. Force

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Correct Answer: Option C

Explanation:
Energy density = energy/volume. Energy has dimensions [ML²T⁻²], volume [L³], so energy density = [ML²T⁻²]/[L³] = [ML⁻¹T⁻²]. Pressure = force/area = [MLT⁻²]/[L²] = [ML⁻¹T⁻²], identical. Force is [MLT⁻²], power [ML²T⁻³], momentum [MLT⁻¹]. This equivalence explains why pressure appears in Bernoulli's equation alongside kinetic/potential energy density. Memory aid: 'Pressure and energy density share dimensions [ML⁻¹T⁻²]'. This dimensional analysis question tests ability to derive and compare formulas, frequently appearing in competitive exams to assess conceptual depth.

This question belongs to: Science Physics

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