Physics MCQs

Question #101

Assertion (A): A convex mirror is used as a rear-view mirror in vehicles. Reason (R): A convex mirror always forms a virtual, erect, and diminished image, giving a wider field of view.

A. Both A and R are true but R is NOT the correct explanation of A.

B. A is true but R is false.

C. A is false but R is true.

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

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Correct Answer: Option D

Explanation:
Convex mirrors bulge outwards, which inherently provides a much wider field of view compared to plane mirrors. Regardless of the object's position, a convex mirror reliably produces virtual, erect, and diminished (smaller) images. This allows a driver to see a large area of the road behind them in a small mirror, making R the exact explanation for A.

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Question #102

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A freely falling body exhibits which type of motion?

A. Non-uniform acceleration

B. Uniform acceleration

C. Zero acceleration

D. Uniform velocity

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Correct Answer: Option B

Explanation:
A freely falling body falls under the sole influence of Earth's gravity (neglecting air resistance). Near the surface of the Earth, the acceleration due to gravity ('g') is constant (approximately 9.8 m/s²). Because the acceleration does not change during the fall, it is an example of uniform accelerated motion.

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Question #103

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What is the primary function of a rectifier in an electrical circuit?

A. To convert Alternating Current (AC) to Direct Current (DC).

B. To measure the flow of current.

C. To convert Direct Current (DC) to Alternating Current (AC).

D. To step up the voltage.

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Correct Answer: Option A

Explanation:
A rectifier is an electrical device composed of one or more diodes that allows current to flow only in one direction. Its primary function is to convert Alternating Current (AC), which periodically reverses direction, into Direct Current (DC), which flows in only one direction. The reverse process (DC to AC) is done by an inverter.

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Question #104

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Which scientist famously demonstrated that a changing magnetic field induces an electromotive force (EMF), discovering electromagnetic induction?

A. Heinrich Lenz

B. Michael Faraday

C. James Clerk Maxwell

D. Nikola Tesla

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Correct Answer: Option B

Explanation:
Michael Faraday discovered electromagnetic induction. He showed that moving a magnet through a coil of wire, or changing the magnetic flux in one coil near another, induces an electrical current. Lenz's law later described the direction of that induced current. Maxwell formulated the classical theory of electromagnetic radiation.

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Question #105

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If a hollow metal sphere is positively charged, the electric field strictly inside the sphere is:

A. Depends on the radius

B. Zero

C. Negative and uniform

D. Positive and uniform

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Correct Answer: Option B

Explanation:
According to Gauss's Law in electrostatics, all excess charge on a conducting body resides entirely on its outer surface. Since there is no net charge enclosed within the hollow interior, the electric flux and consequently the electric field everywhere inside the hollow conducting sphere is exactly zero.

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Question #106

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If the momentum of a body is increased by 50%, what will be the percentage increase in its kinetic energy?

A. 225%

B. 50%

C. 125%

D. 100%

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Correct Answer: Option C

Explanation:
Kinetic energy (K) and momentum (p) are related by K = p^2 / 2m. If momentum increases by 50%, the new momentum p' = p + 0.5p = 1.5p. The new kinetic energy K' = (1.5p)^2 / 2m = 2.25 (p^2 / 2m) = 2.25 K. This means K has increased by 1.25 K, which is a 125% increase. Understanding quadratic relationships is crucial for such problems.

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Question #107

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A projectile is fired at an angle of 45 degrees to the horizontal. The ratio of its maximum height to its horizontal range is:

A. 4:1

B. 1:4

C. 2:1

D. 1:2

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Correct Answer: Option B

Explanation:
The maximum height H = (u^2 * sin^2(theta)) / 2g. The horizontal range R = (u^2 * sin(2theta)) / g. For an angle of 45 degrees, sin(45) = 1/sqrt(2) and sin(90) = 1. H = (u^2 * 0.5) / 2g = u^2 / 4g. R = u^2 / g. Therefore, H/R = (u^2/4g) / (u^2/g) = 1/4. The ratio is 1:4.

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Question #108

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A block of mass 'm' is placed on a rough inclined plane of inclination theta. If the block is just on the verge of sliding down, the coefficient of static friction (mu) is equal to:

A. cot(theta)

B. tan(theta)

C. cos(theta)

D. sin(theta)

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Correct Answer: Option B

Explanation:
When the block is on the verge of sliding (limiting friction), the downward component of weight along the plane equals the maximum static friction force. mgsin(theta) = mu * N. The normal reaction N is balanced by the perpendicular component of weight: N = mgcos(theta). Dividing the two equations gives mgsin(theta) / mgcos(theta) = mu, so mu = tan(theta). This angle is called the angle of repose.

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Question #109

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In a perfectly elastic collision between two bodies, which of the following physical quantities are conserved?

A. Only kinetic energy

B. Only momentum

C. Neither momentum nor kinetic energy

D. Both momentum and kinetic energy

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Correct Answer: Option D

Explanation:
In any collision (elastic or inelastic), the total linear momentum is always conserved, provided no external forces act on the system. However, a perfectly elastic collision is specifically defined as one in which there is absolutely no loss of kinetic energy. Therefore, both total linear momentum and total kinetic energy are conserved.

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Question #110

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The work done by a conservative force acting on a particle moving around any closed path is:

A. Depends on the path taken

B. Positive

C. Negative

D. Zero

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Correct Answer: Option D

Explanation:
By definition, a force is conservative if the work done by it on an object moving between two points is completely independent of the path taken. A direct consequence of this is that the total work done by a conservative force (like gravity or electrostatic force) in moving an object around a closed loop (returning to the starting point) is exactly zero.

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Question #111

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According to Kepler's Third Law of Planetary Motion, the square of the time period of revolution of a planet around the Sun is directly proportional to:

A. The mass of the planet

B. The cube of the semi-major axis of its elliptical orbit

C. The square of the semi-major axis of its elliptical orbit

D. The cube of the mass of the Sun

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Correct Answer: Option B

Explanation:
Kepler's Third Law (Law of Periods) states that the square of the time period (T^2) of any planet is proportional to the cube of the semi-major axis (r^3) of its orbit. Mathematically, T^2 is proportional to r^3. This law helps in calculating orbital periods or distances of planets and satellites.

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Question #112

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At what depth below the surface of the Earth does the acceleration due to gravity become zero?

A. At a depth equal to one-fourth the radius of the Earth

B. It never becomes zero

C. At the center of the Earth

D. At a depth equal to half the radius of the Earth

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Correct Answer: Option C

Explanation:
The acceleration due to gravity at a depth 'd' is given by g' = g(1 - d/R), where R is the radius of the Earth. If we go to the center of the Earth, the depth 'd' becomes exactly equal to R. Substituting d = R into the formula gives g' = g(1 - R/R) = g(1 - 1) = 0. So, gravity is zero at the core.

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Question #113

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A capillary tube is dipped in water and the water rises to a height 'h'. If the experiment is performed in a freely falling elevator, the water column in the tube will:

A. Rise to height 2h

B. Rise to the full length of the capillary tube

C. Not rise at all

D. Rise to height h

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Correct Answer: Option B

Explanation:
The height of capillary rise is given by Jurin's law: h = 2Tcos(theta) / (rrhog). In a freely falling elevator, the effective acceleration due to gravity (g') is zero (weightlessness). As effective g approaches zero, the theoretical height h approaches infinity. In reality, the water will rise to the very top of the tube, regardless of its length, but will not overflow.

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Question #114

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Raindrops fall to the ground with a uniform, constant velocity. This constant velocity is achieved when the gravitational pull is perfectly balanced by:

A. Surface tension of the drop

B. Viscous drag force alone

C. The sum of viscous drag force and buoyant force

D. Buoyant force alone

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Correct Answer: Option C

Explanation:
As a raindrop falls, it accelerates due to gravity. The upward viscous drag force of the air increases with the drop's velocity (Stokes' Law). Eventually, the downward weight of the drop is exactly balanced by the upward buoyant force of the air plus the upward viscous drag force. The net force becomes zero, and it falls with a constant 'terminal velocity'.

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Question #115

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Assertion (A): The coefficient of volume expansion of a solid is approximately three times its coefficient of linear expansion. Reason (R): Volume is a three-dimensional property derived from cubing the linear dimension.

A. A is false but R is true.

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

C. Both A and R are true but R is NOT the correct explanation of A.

D. A is true but R is false.

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Correct Answer: Option B

Explanation:
The coefficient of linear expansion is alpha. A cube of side L has volume V = L^3. When heated, the new length is L(1+alphadT). The new volume is [L(1+alphadT)]^3. Expanding via binomial theorem and ignoring higher-order small terms gives V' = V(1 + 3alphadT). Thus, the volume expansion coefficient gamma is equal to 3alpha. Reason R correctly explains Assertion A.

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Question #116

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Which thermodynamic process occurs at a constant volume?

A. Isochoric process

B. Isothermal process

C. Adiabatic process

D. Isobaric process

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Correct Answer: Option A

Explanation:
An isochoric process is a thermodynamic process in which the volume of the closed system remains constant (delta V = 0). Because there is no change in volume, the system does zero pressure-volume work (W = Pdelta V = 0). According to the first law of thermodynamics, any heat added goes entirely into increasing the internal energy. Isobaric is constant pressure; isothermal is constant temperature.

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Question #117

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The First Law of Thermodynamics is essentially a specific application of which fundamental principle of physics?

A. Conservation of Energy

B. Conservation of Mass

C. Newton's Third Law

D. Conservation of Momentum

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Correct Answer: Option A

Explanation:
The first law of thermodynamics states that the heat supplied to a system (dQ) is equal to the change in its internal energy (dU) plus the work done by the system (dW): dQ = dU + dW. This is the law of conservation of energy applied to thermodynamic systems, stating that energy cannot be created or destroyed, only transferred or changed in form.

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Question #118

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Two waves of identical frequency and amplitude superimpose in the same medium. If they meet perfectly in phase (crest meets crest), the resulting amplitude is:

A. Four times the individual amplitude

B. Zero

C. Same as the individual amplitude

D. Twice the individual amplitude

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Correct Answer: Option D

Explanation:
This is an example of constructive interference. According to the principle of superposition, the resultant displacement is the algebraic sum of individual displacements. If the waves are perfectly in phase, their amplitudes add directly (A + A = 2A). Note that while amplitude doubles, the intensity (which is proportional to amplitude squared) becomes four times greater.

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Question #119

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When a source of sound moves faster than the speed of sound itself in that medium, it creates a conical wave front known as a:

A. Transverse wave

B. Beat frequency

C. Standing wave

D. Shock wave

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Correct Answer: Option D

Explanation:
When an object (like a jet plane) exceeds the speed of sound (Mach 1), it overtakes the sound waves it produces. These sound waves pile up behind the object, superimposing constructively to form an intense, cone-shaped pressure wave called a shock wave. When this high-pressure cone sweeps over an observer on the ground, they hear a loud 'sonic boom'.

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Question #120

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In geometric optics, the power of a lens is defined as the reciprocal of its:

A. Magnification

B. Focal length in meters

C. Refractive index

D. Radius of curvature

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Correct Answer: Option B

Explanation:
The power (P) of a lens indicates its converging or diverging ability. It is mathematically defined as the reciprocal of the focal length (f), provided the focal length is measured in meters. The formula is P = 1 / f(in meters). The SI unit of power for a lens is the Diopter (D). A focal length of 0.5m gives a power of 2D.

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