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 #121
Mirage is an optical illusion observed in hot deserts. It is entirely caused by:
A. Total internal reflection of light
B. Diffraction of light
C. Interference of light
D. Scattering of light
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Correct Answer: Option A

Explanation:
In hot deserts, the sand heats the air immediately above it, making it less dense (optically rarer) than cooler air higher up. Light from a tall object (like the sky or a tree) traveling downwards passes from denser to rarer air layers, bending away from the normal. Eventually, the angle of incidence exceeds the critical angle, causing total internal reflection. The observer perceives this reflected light as a pool of water on the ground.
This question belongs to: Science Physics
Question #122
According to Coulomb's Law, what happens to the electric force if a dielectric medium (like glass or water) is introduced between two point charges?
A. The force drops immediately to zero.
B. The force increases.
C. The force decreases.
D. The force remains identical.
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Correct Answer: Option C

Explanation:
Coulomb's force in a vacuum is F = (1/4piepsilon_0) * (q1q2/r^2). When a dielectric medium with relative permittivity (dielectric constant) 'K' is introduced, the new force is F' = F / K. Since K > 1 for all insulating materials (e.g., K for water is ~80), the electrostatic force between the charges is significantly reduced by the medium.
This question belongs to: Science Physics
Question #123
The work done in moving a unit positive charge from one point to another against an electric field is known as:
A. Potential Difference
B. Electric Field Intensity
C. Capacitance
D. Electric Flux
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Correct Answer: Option A

Explanation:
By definition, the electric potential difference between two points in an electric field is the amount of external work required to move a unit positive charge (1 Coulomb) slowly and without acceleration from one point to the other against the electrostatic force. The SI unit of potential difference is the Volt (Joules/Coulomb).
This question belongs to: Science Physics
Question #124
Kirchhoff's First Law (Junction Rule) for electrical circuits is based entirely on the principle of conservation of:
A. Mass
B. Energy
C. Momentum
D. Charge
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Correct Answer: Option D

Explanation:
Kirchhoff's Current Law (First Law) states that the total current entering a junction must exactly equal the total current leaving that junction. Current is the rate of flow of charge. Therefore, this law simply affirms that electric charge cannot be created or destroyed at a circuit node; all charge arriving must depart. It is the conservation of charge.
This question belongs to: Science Physics
Question #125
Which of the following materials is diamagnetic in nature?
A. Iron
B. Aluminum
C. Water
D. Nickel
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Correct Answer: Option C

Explanation:
Materials are classified by their magnetic properties. Ferromagnetic materials (Iron, Cobalt, Nickel) are strongly attracted to magnets. Paramagnetic materials (Aluminum, Platinum) are weakly attracted. Diamagnetic materials (Water, Bismuth, Copper, Gold) are actually weakly repelled by a magnetic field because they create an induced magnetic field in opposition to the externally applied one.
This question belongs to: Science Physics
Question #126
The magnetic field inside a long, straight, current-carrying solenoid is:
A. Directly proportional to the radius of the solenoid
B. Uniform (same at all points)
C. Stronger at the ends than at the center
D. Zero
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Correct Answer: Option B

Explanation:
An ideal solenoid consists of tightly packed coils. When current passes through it, the magnetic field lines inside the solenoid are parallel straight lines. This indicates that the magnetic field is uniform in magnitude and direction at all points strictly inside the central region of the solenoid. The field strength is given by B = mu_0 * n * I.
This question belongs to: Science Physics
Question #127
According to Lenz's Law, the direction of an induced current is such that it:
A. Maximizes the change in magnetic flux.
B. Creates a perfect vacuum in the coil.
C. Opposes the exact cause that produces it.
D. Aligns entirely with the external magnetic field.
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Correct Answer: Option C

Explanation:
Lenz's law is a consequence of the conservation of energy. It dictates that an induced electromotive force (EMF) always gives rise to a current whose magnetic field opposes the change in original magnetic flux that produced it. If a north pole approaches a coil, the coil face becomes a north pole to repel the magnet, requiring work to overcome.
This question belongs to: Science Physics
Question #128
In the photoelectric effect, increasing the intensity of the incident light (while keeping frequency constant) will cause:
A. An increase in the number of emitted photoelectrons per second.
B. A decrease in the maximum kinetic energy of the emitted electrons.
C. An increase in the maximum kinetic energy of the emitted electrons.
D. A change in the threshold frequency of the metal surface.
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Correct Answer: Option A

Explanation:
According to Einstein's photoelectric equation, the kinetic energy of emitted electrons depends exclusively on the frequency of the incident light and the metal's work function. Intensity represents the number of photons striking the surface per second. More photons mean more collisions with electrons, leading strictly to an increase in the number of emitted photoelectrons (photoelectric current), not their energy.
This question belongs to: Science Physics
Question #129
The de Broglie wavelength associated with a moving particle is inversely proportional to its:
A. Kinetic energy
B. Velocity only
C. Momentum
D. Mass only
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Correct Answer: Option C

Explanation:
Louis de Broglie proposed that matter exhibits wave-like properties. The de Broglie wavelength (lambda) of a particle is given by the formula lambda = h / p, where 'h' is Planck's constant and 'p' is the linear momentum (mass * velocity) of the particle. Therefore, the wavelength is strictly inversely proportional to the momentum of the moving particle.
This question belongs to: Science Physics
Question #130
What happens to the atomic number and mass number of a radioactive nucleus when it emits a gamma ray?
A. Both atomic number and mass number remain completely unchanged.
B. Atomic number increases by 1, mass number remains the same.
C. Both atomic number and mass number decrease by 1.
D. Atomic number decreases by 2, mass number decreases by 4.
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Correct Answer: Option A

Explanation:
Gamma emission is the release of high-energy electromagnetic radiation (photons) from a nucleus transitioning from an excited high-energy state to a lower, stable energy state. Gamma rays carry no mass and no electrical charge. Therefore, the emission of a gamma ray does not alter the number of protons (atomic number) or the total number of nucleons (mass number) of the atom.
This question belongs to: Science Physics
Question #131
Which scientific instrument is explicitly designed for measuring extremely small lengths with high precision by using a main scale and a rotating circular scale?
A. Spherometer
B. Screw Gauge (Micrometer)
C. Vernier Caliper
D. Spectrometer
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Correct Answer: Option B

Explanation:
A micrometer screw gauge uses the principle of a screw rotating in a nut to measure very tiny dimensions (like the diameter of a thin wire). It features a linear main scale and a rotating circular scale on the thimble. While a Vernier caliper measures small distances using sliding scales, the screw gauge generally offers greater precision (least count often 0.01 mm or 0.001 mm).
This question belongs to: Science Physics
Question #132
A typical household refrigerator works by forcing a refrigerant fluid through a cycle of:
A. Ionization and recombination
B. Sublimation and deposition
C. Nuclear fission and fusion
D. Evaporation and condensation
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Correct Answer: Option D

Explanation:
A refrigerator is a heat pump operating in reverse. A compressor squeezes the refrigerant gas, raising its temperature. As it passes through coils on the back (condenser), it releases heat and condenses into a liquid. This liquid expands through a valve, cooling rapidly, and flows into the evaporator coils inside the fridge, where it absorbs heat from the food and evaporates back into a gas.
This question belongs to: Science Physics
Question #133
Which of the following scientists formulated the 'Uncertainty Principle', stating that exact position and momentum of an electron cannot be simultaneously known?
A. Werner Heisenberg
B. Erwin Schrodinger
C. Max Planck
D. Niels Bohr
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Correct Answer: Option A

Explanation:
Werner Heisenberg, a German theoretical physicist, published his famous Uncertainty Principle in 1927. The principle dictates a fundamental limit to precision at the quantum level: the more precisely the position of a particle (like an electron) is determined, the less precisely its momentum can be known, and vice versa. Mathematically, delta_x * delta_p >= h/(4pi).
This question belongs to: Science Physics
Question #134
If the length of a wire is stretched to double its original length while keeping its volume constant, its new resistance will be:
A. Four times the original
B. Twice the original
C. Unchanged
D. Half the original
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Correct Answer: Option A

Explanation:
Resistance R = rhoL/A. If the wire is stretched so length becomes L' = 2L, the volume (V = AL) must remain constant. Therefore, the new area A' must be A/2 to maintain V. The new resistance R' = rho(2L)/(A/2) = 4 * (rhoL/A) = 4R. Stretching a wire to double its length increases its resistance strictly by a factor of 4. This is a classic trap question compared to merely 'changing the wire'.
This question belongs to: Science Physics
Question #135
When a body is moving in a uniform circular motion, the work done by the centripetal force is zero because:
A. The body has no kinetic energy.
B. The force is balanced by an outward centrifugal force.
C. The force is extremely weak.
D. The force is always perpendicular to the instantaneous displacement.
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Correct Answer: Option D

Explanation:
Work done is given by W = F * d * cos(theta). In uniform circular motion, the centripetal force is always directed strictly towards the center of the circle, while the instantaneous displacement (velocity vector) is tangential to the circle. The angle (theta) between them is exactly 90 degrees. Since cos(90) = 0, the work done by the centripetal force is always zero.
This question belongs to: Science Physics
Question #136
In a p-n junction diode, the depletion region is created primarily due to:
A. Heating of the semiconductor material.
B. Drift of electrons under a strong electric field.
C. Diffusion of majority charge carriers across the junction.
D. Recombination of minority carriers.
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Correct Answer: Option C

Explanation:
When a p-type and an n-type semiconductor are joined, electrons from the n-side (majority carriers) diffuse across the junction to the p-side, and holes from the p-side diffuse to the n-side due to concentration gradients. They recombine near the junction, leaving behind immobile ionized atoms (positive donor ions on n-side, negative acceptor ions on p-side). This uncovered charge region is the depletion layer.
This question belongs to: Science Physics
Question #137
The working of an optical fiber is based primarily on the phenomenon of:
A. Dispersion of light
B. Polarization of light
C. Total internal reflection
D. Diffraction of light
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Correct Answer: Option C

Explanation:
Optical fibers consist of a central core surrounded by a cladding with a slightly lower refractive index. When a light beam enters the core at an angle greater than the critical angle, it undergoes multiple successive total internal reflections against the core-cladding boundary. This allows the light to travel over vast distances with virtually no loss of energy, making it ideal for telecommunications.
This question belongs to: Science Physics
Question #138
A transformer has 50 turns in the primary coil and 1000 turns in the secondary coil. If the primary voltage is 220V, what is the secondary voltage?
A. 22000 V
B. 440 V
C. 4400 V
D. 11 V
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Correct Answer: Option C

Explanation:
The transformer equation relates voltages to the number of turns: V_secondary / V_primary = N_secondary / N_primary. We have N_p = 50, N_s = 1000, and V_p = 220V. Substituting the values gives V_s / 220 = 1000 / 50. V_s = 220 * 20 = 4400 Volts. This is a step-up transformer, increasing the voltage strictly by a factor of 20.
This question belongs to: Science Physics
Question #139
Which famous physicist correctly formulated the laws of electromagnetic induction mathematically, later synthesizing all known electromagnetic phenomena into four fundamental equations?
A. James Clerk Maxwell
B. André-Marie Ampère
C. Heinrich Hertz
D. Michael Faraday
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Correct Answer: Option A

Explanation:
While Faraday performed the groundbreaking experimental work discovering electromagnetic induction, it was James Clerk Maxwell who formalized these discoveries mathematically. Maxwell's equations (a set of four differential equations) elegantly united electricity, magnetism, and optics, proving theoretically that light itself is a propagating electromagnetic wave.
This question belongs to: Science Physics
Question #140
An AC generator produces alternating current. To convert an AC generator into a DC generator, which crucial component must be replaced?
A. The magnetic poles must be swapped.
B. The split-ring commutator must be replaced with slip rings.
C. The slip rings must be replaced with a split-ring commutator.
D. The armature coil must be made of aluminum.
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Correct Answer: Option C

Explanation:
An AC generator uses continuous 'slip rings' which allow the output polarity to reverse every half-rotation of the coil, generating alternating current. To produce direct current (DC), the slip rings must be replaced by a 'split-ring commutator'. This commutator reverses the connections to the external circuit at the exact moment the coil's current reverses, ensuring current flows in only one direction outside.
This question belongs to: Science Physics

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