Physics MCQs

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Physics MCQs

Practice the latest Physics MCQs with answers and detailed explanations. This section includes chapter-wise multiple-choice questions covering mechanics, motion, force, work and energy, heat, light, electricity, magnetism, modern physics, waves, optics, and other important topics. These exam-oriented MCQs are ideal for Class 9–12, NEET, JEE, CUET, SSC, Banking, Railway, JKSSB, Defence, Police, and other competitive exams.

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Page 4 of 65
Question #61
The dimensions of surface tension are the same as that of:
A. Force
B. Viscosity
C. Pressure
D. Spring constant
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Correct Answer: Option D

Explanation:
Surface tension is defined as Force per unit length (F/L). Dimensional formula: [MLT⁻²] / [L] = [MT⁻²]. A spring constant (k) is defined by Hooke's Law as Force per unit extension (F/x), which also has dimensions [MLT⁻²] / [L] = [MT⁻²]. Thus, both share the same dimensional formula.
This question belongs to: Science Physics
Question #62
If a stone is tied to a string and whirled in a circle, and the string suddenly breaks, the stone will:
A. Move inwards towards the center.
B. Fall straight down immediately due to gravity.
C. Fly off tangentially to the circular path.
D. Fly outwards radially.
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Correct Answer: Option C

Explanation:
When the stone is moving in a circle, its velocity vector is always tangential to the circle. The string provides the necessary centripetal force directed towards the center. When the string breaks, this inward force ceases to exist. Due to inertia of direction (Newton's First Law), the stone continues to move along the tangent at the point where the string broke.
This question belongs to: Science Physics
Question #63
The efficiency of an ideal Carnot engine operating between two temperatures T1 (source) and T2 (sink) is given by:
A. 1 - (T2/T1)
B. 1 - (T1/T2)
C. T2 / (T1 - T2)
D. (T1 - T2) / T2
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Correct Answer: Option A

Explanation:
The thermal efficiency (η) of a reversible Carnot engine depends exclusively on the absolute temperatures of the hot source (T1) and the cold sink (T2). The formula is η = 1 - (T2/T1), or (T1 - T2) / T1. Temperatures must be in Kelvin. It shows no engine can be 100% efficient unless the sink is at absolute zero.
This question belongs to: Science Physics
Question #64
A transformer works on the principle of:
A. Electromagnetic repulsion
B. Electrostatic induction
C. Self-induction
D. Mutual induction
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Correct Answer: Option D

Explanation:
A transformer operates on the principle of mutual induction. It consists of primary and secondary coils. When an alternating current flows through the primary coil, it generates a changing magnetic field. This fluctuating flux links with the secondary coil, inducing an alternating electromotive force (EMF) in it according to Faraday's Law.
This question belongs to: Science Physics
Question #65
Identify the incorrect statement regarding the human eye.
A. The retina acts as the screen where images are formed.
B. The cornea provides most of the eye's refractive power.
C. The image formed on the retina is virtual and erect.
D. The pupil regulates the amount of light entering the eye.
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Correct Answer: Option C

Explanation:
The eye lens is a convex (converging) lens. It converges light rays to form a real and inverted image on the retina. The brain processes this signal and flips it so we perceive the world as erect. All other statements are functionally correct. The cornea does indeed do about two-thirds of the focusing.
This question belongs to: Science Physics
Question #66
Assertion (A): When ice floats in water, its approximately 1/10th volume remains outside the water. Reason (R): The density of ice is approximately 10% less than the density of water.
A. A is false but R is true.
B. Both A and R are true and R is the correct explanation of A.
C. A is true but R is false.
D. Both A and R are true but R is NOT the correct explanation of A.
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Correct Answer: Option B

Explanation:
The density of ice is about 900 kg/m³ (0.9 g/cm³), while pure water is 1000 kg/m³ (1.0 g/cm³). According to the principle of floatation, the fraction of volume submerged is the ratio of densities: ρ_ice / ρ_water = 0.9. This means 90% is submerged, leaving exactly 10% (1/10th) exposed above the surface. Reason R explains Assertion A.
This question belongs to: Science Physics
Question #67
What is the equivalent resistance when n identical resistors, each of resistance R, are connected in series, compared to when they are connected in parallel?
A. Series resistance is n times the parallel resistance.
B. Series resistance is equal to the parallel resistance.
C. Parallel resistance is n² times the series resistance.
D. Series resistance is n² times the parallel resistance.
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Correct Answer: Option D

Explanation:
When n resistors of resistance R are in series, Rs = nR. When connected in parallel, Rp = R/n. To find the ratio, Rs / Rp = (nR) / (R/n) = n². Therefore, the series resistance is n² times the equivalent parallel resistance. This is a highly frequent numerical shortcut for exams.
This question belongs to: Science Physics
Question #68
A ball is dropped from a height 'h' and simultaneously another ball is thrown horizontally from the same height. Which ball will hit the ground first? (Neglect air resistance)
A. The dropped ball
B. Both will hit the ground simultaneously
C. The horizontally thrown ball
D. Depends on the initial horizontal velocity
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Correct Answer: Option B

Explanation:
Vertical and horizontal motions are completely independent. Both balls have zero initial downward (vertical) velocity and both are subject to the same downward acceleration due to gravity (g). Since the vertical height (h) is the same, using h = ut + ½gt², time t = √(2h/g) applies equally to both. Thus, they hit the ground simultaneously.
This question belongs to: Science Physics
Question #69
The time period of a geostationary satellite is:
A. 27.3 days
B. 12 hours
C. 24 hours
D. 365 days
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Correct Answer: Option C

Explanation:
A geostationary satellite orbits the Earth directly over the equator at an altitude of ~35,786 km. It revolves in the same direction the Earth rotates. Its orbital period perfectly matches Earth's rotational period, which is 24 hours. Because of this, it appears entirely stationary from any point on Earth's surface, making it ideal for communications and DTH TV.
This question belongs to: Science Physics
Question #70
Which of the following colors of light has the lowest frequency?
A. Green
B. Violet
C. Red
D. Blue
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Correct Answer: Option C

Explanation:
In the visible spectrum (VIBGYOR), wavelength increases from Violet to Red. Since speed = frequency × wavelength (c = fλ), frequency is inversely proportional to wavelength. Red light has the longest wavelength and therefore the lowest frequency and lowest energy. Violet has the shortest wavelength and highest frequency.
This question belongs to: Science Physics
Question #71
The phenomenon of electromagnetic induction was discovered by:
A. Michael Faraday
B. Heinrich Hertz
C. Nikola Tesla
D. Thomas Edison
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Correct Answer: Option A

Explanation:
Michael Faraday discovered electromagnetic induction in 1831. He demonstrated that a changing magnetic field could induce an electric current in a nearby circuit. This groundbreaking discovery laid the foundation for all modern electric generators and transformers. Tesla contributed to AC systems, Edison to DC systems, and Hertz proved the existence of radio waves.
This question belongs to: Science Physics
Question #72
If an object is placed at the center of curvature of a concave mirror, the image formed is:
A. Virtual, erect, and magnified.
B. Real, inverted, and of the same size.
C. Real, inverted, and magnified.
D. Virtual, erect, and diminished.
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Correct Answer: Option B

Explanation:
For a concave mirror, when an object is placed exactly at the center of curvature (C), the image is also formed at C. The image is real (can be captured on a screen), inverted (upside down), and exactly the same size as the object. Magnification in this specific case is exactly -1.
This question belongs to: Science Physics
Question #73
Beta rays emitted by radioactive substances are essentially:
A. Helium nuclei
B. High-speed electrons
C. Electromagnetic waves
D. Neutrons
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Correct Answer: Option B

Explanation:
During beta decay, a neutron in an unstable nucleus transforms into a proton and an electron. The proton remains in the nucleus, but the electron is ejected at high speed. These ejected, high-energy electrons are called beta rays (or beta particles). Gamma rays are electromagnetic waves, and alpha particles are helium nuclei.
This question belongs to: Science Physics
Question #74
The energy of an object due to its specific position or configuration is known as:
A. Mechanical Energy
B. Kinetic Energy
C. Thermal Energy
D. Potential Energy
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Correct Answer: Option D

Explanation:
Potential energy is the stored energy an object possesses due to its position relative to other objects, stresses within itself, its electric charge, or other factors. For example, water stored in a dam has gravitational potential energy, and a compressed spring has elastic potential energy.
This question belongs to: Science Physics
Question #75
If the length and cross-sectional area of a wire are both doubled, its resistance will:
A. Quadruple
B. Remain unchanged
C. Halve
D. Double
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Correct Answer: Option B

Explanation:
Resistance (R) of a wire is given by R = ρL/A, where ρ is resistivity, L is length, and A is cross-sectional area. If L becomes 2L and A becomes 2A, the new resistance is R' = ρ(2L)/(2A). The 2s cancel out, leaving R' = ρL/A = R. Thus, the resistance remains entirely unchanged.
This question belongs to: Science Physics
Question #76
A lactometer operates on the principle of:
A. Pascal's Law
B. Archimedes' Principle
C. Bernoulli's Theorem
D. Newton's Law of Viscosity
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Correct Answer: Option B

Explanation:
A lactometer is a specific type of hydrometer used to test the purity of milk by measuring its relative density. All hydrometers, including lactometers, work on Archimedes' Principle of buoyancy. They float at a depth that depends directly on the density of the liquid; they sink deeper in less dense liquids (like milk heavily diluted with water).
This question belongs to: Science Physics
Question #77
Which component in an electrical circuit is specifically designed to melt and break the circuit in the event of an overload?
A. Switch
B. Fuse
C. Capacitor
D. Resistor
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Correct Answer: Option B

Explanation:
A fuse is an electrical safety device consisting of a wire made of an alloy with a low melting point. If the current exceeds a safe limit (due to a short circuit or overload), the Joules heating (I²Rt) causes the wire to melt instantly, breaking the circuit and preventing fire or damage to appliances.
This question belongs to: Science Physics
Question #78
When a wave travels from one medium to another, which of its properties never changes?
A. Frequency
B. Velocity
C. Wavelength
D. Amplitude
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Correct Answer: Option A

Explanation:
When a wave (like light or sound) changes mediums, its velocity changes due to the new medium's optical or mechanical density. Wavelength changes proportionally with velocity (v = fλ). However, frequency is determined solely by the source generating the wave and the energy of the photons/particles, and it remains absolutely constant.
This question belongs to: Science Physics
Question #79
Light emitting diodes (LEDs) are preferred over incandescent bulbs primarily because:
A. They emit a wider spectrum of light.
B. They are highly energy-efficient and convert most energy into light.
C. They consume more power but last longer.
D. They rely on a heated filament.
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Correct Answer: Option B

Explanation:
Incandescent bulbs work by heating a tungsten filament until it glows, converting roughly 90% of electrical energy into wasted heat and only 10% into light. LEDs are solid-state semiconductors that emit light through electroluminescence. They convert almost all their electrical energy directly into light, making them significantly more efficient and cooler.
This question belongs to: Science Physics
Question #80
In a nuclear reaction, mass defect refers to:
A. The mass gained during a fusion reaction.
B. The mass of the neutrons emitted.
C. The mass converted purely into radioactive waste.
D. The difference between the mass of reactants and the mass of products.
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Correct Answer: Option D

Explanation:
In nuclear reactions, the total mass of the products is slightly less than the total mass of the original reacting nuclei. This missing mass is known as the 'mass defect'. According to Einstein's mass-energy equivalence principle (E = mc²), this tiny amount of missing mass is converted into the tremendous energy released during the reaction.
This question belongs to: Science Physics

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