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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Question #181
When a small spherical metal body falls through a highly viscous liquid, it attains a terminal velocity. This terminal velocity is directly proportional to:
A. The radius of the sphere
B. The square of the radius of the sphere
C. The inverse of the radius of the sphere
D. The square root of the radius of the sphere
Discuss
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Correct Answer: Option B

Explanation:
According to Stokes' Law, the terminal velocity (Vt) of a spherical body falling through a viscous medium is given by Vt = 2r^2(rho - sigma)g / 9(eta). Here, r is the radius. The formula clearly shows that the terminal velocity is directly proportional to the square of the radius (r^2).
This question belongs to: Science Physics
Question #182
According to Newton's Law of Cooling, the rate of loss of heat from a body is strictly proportional to:
A. The temperature difference between the body and its surroundings.
B. The square of the temperature of the body.
C. The absolute temperature of the surroundings.
D. The fourth power of the temperature difference.
Discuss
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Correct Answer: Option A

Explanation:
Newton's Law of Cooling is a practical approximation stating that the rate of heat loss of a body is directly proportional to the difference in temperatures between the body and its immediate environment, provided this temperature difference is relatively small. The equation is dQ/dt = -k(T_body - T_surroundings).
This question belongs to: Science Physics
Question #183
Stefan-Boltzmann Law states that the total radiant heat energy emitted from a perfectly black body is proportional to:
A. T^2
B. T^4
C. T^3
D. T
Discuss
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Correct Answer: Option B

Explanation:
The Stefan-Boltzmann law dictates that the total energy radiated per unit surface area of a black body across all wavelengths per unit time (Emissive Power, E) is strictly directly proportional to the fourth power of the black body's thermodynamic (absolute) temperature. E = sigma * T^4, where sigma is the Stefan-Boltzmann constant.
This question belongs to: Science Physics
Question #184
According to Wien's Displacement Law, if the absolute temperature of a radiating black body is doubled, the wavelength corresponding to maximum spectral emissive power will:
A. Double
B. Halve
C. Remain unchanged
D. Increase four times
Discuss
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Correct Answer: Option B

Explanation:
Wien's Displacement Law states that the wavelength at which a black body emits maximum radiation (lambda_m) is inversely proportional to its absolute temperature (T). lambda_m * T = b (Wien's constant). If the temperature T is doubled (2T), the peak wavelength lambda_m must strictly halve to maintain the constant product.
This question belongs to: Science Physics
Question #185
Two slabs of equal thickness and cross-sectional area have thermal conductivities K1 and K2. If they are joined in series, the equivalent thermal conductivity of the combination is:
A. K1 * K2 / (K1 + K2)
B. 2K1 * K2 / (K1 + K2)
C. (K1 + K2) / 2
D. sqrt(K1^2 + K2^2)
Discuss
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Correct Answer: Option B

Explanation:
For slabs in series, the rate of heat flow (H) is the same. Total resistance R_eq = R1 + R2. Since thermal resistance R = L / (KA), and total length is 2L: (2L) / (K_eq * A) = (L / K1A) + (L / K2A). Canceling L/A yields 2/K_eq = 1/K1 + 1/K2. Solving gives K_eq = 2K1K2 / (K1 + K2).
This question belongs to: Science Physics
Question #186
For an organ pipe completely closed at one end, the fundamental frequency is f. What are the frequencies of the next two higher harmonics?
A. 4f and 6f
B. 2f and 4f
C. 3f and 5f
D. 2f and 3f
Discuss
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Correct Answer: Option C

Explanation:
An organ pipe closed at one end features a node at the closed end and an antinode at the open end. Because of these boundary conditions, it can only support odd harmonics. If the fundamental frequency (1st harmonic) is f, the next permissible frequencies are the 3rd harmonic (3f), 5th harmonic (5f), 7th harmonic (7f), and so forth.
This question belongs to: Science Physics
Question #187
If the intensity of a sound is mathematically increased by a factor of 100, its loudness level in decibels (dB) increases strictly by:
A. 2 dB
B. 20 dB
C. 10 dB
D. 100 dB
Discuss
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Correct Answer: Option B

Explanation:
The loudness level in decibels is calculated as L = 10 * log10(I / I0). If intensity I becomes 100I, the new level L' = 10 * log10(100I / I0) = 10 * [log10(100) + log10(I / I0)] = 10 * [2 + L/10] = 20 + L. Therefore, the loudness explicitly increases by 20 dB.
This question belongs to: Science Physics
Question #188
Two waves interfering at a point have a path difference of lambda / 2. Their corresponding phase difference is exactly:
A. pi / 2 radians
B. pi / 4 radians
C. 2pi radians
D. pi radians
Discuss
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Correct Answer: Option D

Explanation:
The relationship between phase difference (phi) and path difference (delta x) is given by the formula phi = (2pi / lambda) * delta x. Given a path difference of lambda / 2, substitute this into the formula: phi = (2pi / lambda) * (lambda / 2) = pi radians. This indicates strictly destructive interference.
This question belongs to: Science Physics
Question #189
According to Brewster's Law, when unpolarized light is incident on a transparent medium at the polarizing angle (Brewster's angle), the reflected and refracted rays are:
A. Totally internally reflected
B. At exactly 90 degrees to each other
C. At 45 degrees to each other
D. Parallel to each other
Discuss
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Correct Answer: Option B

Explanation:
Brewster's Law states that when light hits a dielectric boundary at a specific angle of incidence (Brewster's angle, theta_p), the reflected light is completely plane-polarized. At this exact geometric condition, the angle between the reflected ray and the refracted (transmitted) ray is strictly 90 degrees.
This question belongs to: Science Physics
Question #190
The resolving power of an astronomical telescope can be significantly increased by:
A. Decreasing the focal length of the eyepiece.
B. Increasing the aperture (diameter) of the objective lens.
C. Using light of a longer wavelength.
D. Increasing the focal length of the objective lens.
Discuss
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Correct Answer: Option B

Explanation:
Resolving power is a telescope's ability to distinguish closely spaced objects (like double stars) as separate. It is proportional to D / lambda, where D is the diameter (aperture) of the objective lens and lambda is the wavelength of light. Increasing the aperture D directly and strictly increases the resolving power.
This question belongs to: Science Physics
Question #191
Kirchhoff's Voltage Law (KVL), which states that the algebraic sum of all potential differences in any closed loop is zero, is a direct manifestation of the conservation of:
A. Mass
B. Energy
C. Linear Momentum
D. Electric Charge
Discuss
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Correct Answer: Option B

Explanation:
Kirchhoff's Second Law (KVL) is based on the principle that the electrostatic field is conservative. The work done (energy spent or gained) in moving a unit charge completely around a closed electrical loop must be zero. Therefore, the sum of voltage drops and EMFs is zero. This strictly represents the Law of Conservation of Energy.
This question belongs to: Science Physics
Question #192
A Wheatstone bridge is said to be completely balanced when:
A. The battery supplies zero current.
B. All four resistors have exactly identical values.
C. Potential difference across the galvanometer is zero.
D. Current through the galvanometer is maximum.
Discuss
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Correct Answer: Option C

Explanation:
A Wheatstone bridge circuit consists of four arms with resistances P, Q, R, S and a galvanometer in the middle. It is balanced when no current flows through the galvanometer arm. This happens exclusively when the potentials at the two ends of the galvanometer are equal, meaning the potential difference across it is exactly zero (P/Q = R/S).
This question belongs to: Science Physics
Question #193
The primary principle behind the working of a potentiometer is that the potential drop across any length of a uniform wire carrying a constant steady current is:
A. Directly proportional to its length.
B. Independent of its length.
C. Inversely proportional to its length.
D. Directly proportional to the square of its length.
Discuss
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Correct Answer: Option A

Explanation:
A potentiometer uses a long wire of uniform cross-section and composition. When a constant steady current flows through it, Ohm's law (V = IR) and the resistance formula (R = rhoL/A) combine to give V = I(rho/A)L. Since I, rho, and A are constant, the potential drop V is strictly directly proportional to the length L of the wire.
This question belongs to: Science Physics
Question #194
Two electric bulbs rated 60W, 220V and 100W, 220V are connected strictly in series across a 220V supply. Which bulb will glow brighter?
A. Both will glow with equal brightness.
B. Neither will glow.
C. 60W bulb
D. 100W bulb
Discuss
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Correct Answer: Option C

Explanation:
Resistance of a bulb is R = V^2 / P. The 60W bulb has a higher resistance than the 100W bulb. When connected in series, the exact same current (I) flows through both. The power consumed (which determines brightness) is given by P = I^2R. Since the 60W bulb has higher resistance (R), it consumes more power and glows brighter.
This question belongs to: Science Physics
Question #195
What is the magnetic dipole moment of an electron revolving in a circular orbit of radius 'r' with a uniform speed 'v'?
A. evr
B. e / (vr)
C. 2evr
D. evr / 2
Discuss
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Correct Answer: Option D

Explanation:
Magnetic dipole moment M = Current(I) * Area(A). Current is charge/time: I = e / T. Time period T = 2pir / v. So I = ev / (2pir). The area of the circular orbit is A = pir^2. Therefore, M = [ev / (2pir)] * [pir^2] = evr / 2. This is a standard derivation in modern physics.
This question belongs to: Science Physics
Question #196
Soft iron is universally preferred for making the core of a transformer or an electromagnet because it possesses:
A. Low retentivity and low coercivity
B. High retentivity and low coercivity
C. Low retentivity and high coercivity
D. High retentivity and high coercivity
Discuss
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Correct Answer: Option A

Explanation:
A transformer core is subject to alternating magnetic fields, tracing out a hysteresis loop repeatedly. To minimize energy loss (hysteresis loss), the area of this loop must be small, requiring low coercivity (easily demagnetized). It also requires low retentivity so it loses magnetism rapidly when current stops. Steel, conversely, has high retentivity and coercivity, used for permanent magnets.
This question belongs to: Science Physics
Question #197
At the magnetic poles of the Earth, the angle of dip (inclination) is exactly:
A. 180 degrees
B. 0 degrees
C. 45 degrees
D. 90 degrees
Discuss
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Correct Answer: Option D

Explanation:
The angle of dip is the angle the Earth's total magnetic field vector makes with the horizontal surface. At the magnetic equator, the magnetic field lines are perfectly parallel to the ground (0 degrees). At the magnetic poles, the field lines plunge strictly vertically downward (or upward) into the ground, making a 90-degree angle with the horizontal.
This question belongs to: Science Physics
Question #198
A positively charged particle is projected precisely parallel to a uniform magnetic field. The trajectory of the particle will be a:
A. Circle
B. Parabola
C. Helix
D. Straight line
Discuss
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Correct Answer: Option D

Explanation:
The magnetic Lorentz force on a moving charge is F = q(v x B) = qvBsin(theta). If the particle moves completely parallel to the magnetic field, the angle theta is 0 degrees. Since sin(0) = 0, the magnetic force is absolutely zero. Experiencing no transverse force, the particle continues moving in a perfect straight line.
This question belongs to: Science Physics
Question #199
In a photoelectric effect experiment, a graph is plotted between the stopping potential (V0) on the y-axis and the frequency of incident light (v) on the x-axis. The slope of this straight line gives the value of:
A. Planck's constant divided by electron charge (h/e)
B. Planck's constant (h)
C. Speed of light (c)
D. Work function of the metal
Discuss
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Correct Answer: Option A

Explanation:
Einstein's photoelectric equation is K_max = hv - W. Since K_max = eV0 (where V0 is stopping potential), eV0 = hv - W. Rearranging for the y-axis variable gives V0 = (h/e)v - (W/e). This is a linear equation y = mx + c. The slope 'm' of the V0 vs v graph is strictly exactly h/e.
This question belongs to: Science Physics
Question #200
According to the Bohr model of the hydrogen atom, the total energy of an electron in the nth stationary orbit is directly proportional to:
A. 1 / n^2
B. n
C. 1 / n
D. n^2
Discuss
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Correct Answer: Option A

Explanation:
The total energy of an electron in a hydrogen-like atom in the nth orbit is strictly negative and given by the mathematical formula E_n = -13.6 Z^2 / n^2 (in eV). This formula demonstrates that the total energy is inversely proportional to the square of the principal quantum number (n^2).
This question belongs to: Science Physics

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