Free Class 12 Physics MCQs – NCERT-Based Practice
Free Class 12 Physics MCQs– Online Practice — Practice Questions
1. The electric field inside a conductor in electrostatic equilibrium is:
- (A) Maximum at the centre
- (B) Zero
- (C) Equal to the applied electric field
- (D) Infinite
Answer: (B) Zero
In electrostatic equilibrium, free charges redistribute until the electric field inside the conductor becomes zero.
2. The SI unit of electric flux is:
- (A) N/C
- (B) N·m²/C
- (C) C/N
- (D) V/m
Answer: (B) N·m²/C
Electric flux is the product of electric field and area. Its SI unit is N·m²/C.
3. Two capacitors of capacitance 3 μF and 6 μF are connected in parallel. The equivalent capacitance is:
- (A) 2 μF
- (B) 9 μF
- (C) 18 μF
- (D) 3 μF
Answer: (B) 9 μF
Capacitors connected in parallel add directly, so Ceq = 3 + 6 = 9 μF.
4. The drift velocity of electrons in a conductor depends directly on:
- (A) Resistance only
- (B) Applied electric field
- (C) Length of the conductor only
- (D) Temperature only
Answer: (B) Applied electric field
Drift velocity is directly proportional to the applied electric field.
5. The Wheatstone bridge is balanced when:
- (A) P + Q = R + S
- (B) P/Q = R/S
- (C) P × Q = R × S
- (D) P − Q = R − S
Answer: (B) P/Q = R/S
The bridge is balanced when the ratio of resistances in one arm equals the ratio in the other arm.
6. A moving charge experiences maximum magnetic force when the angle between velocity and magnetic field is:
- (A) 0°
- (B) 30°
- (C) 60°
- (D) 90°
Answer: (D) 90°
Magnetic force is maximum when the velocity is perpendicular to the magnetic field.
7. The magnetic field inside a long straight solenoid is:
- (A) Zero
- (B) Uniform
- (C) Non-uniform
- (D) Circular
Answer: (B) Uniform
A long solenoid produces a nearly uniform magnetic field inside it.
8. According to Faraday's law, induced emf is proportional to the:
- (A) Magnetic field only
- (B) Rate of change of magnetic flux
- (C) Area only
- (D) Resistance of the circuit
Answer: (B) Rate of change of magnetic flux
Induced emf equals the negative rate of change of magnetic flux.
9. Lenz's law is a consequence of the law of conservation of:
- (A) Charge
- (B) Momentum
- (C) Energy
- (D) Mass
Answer: (C) Energy
Lenz's law ensures that induced current opposes the change producing it, conserving energy.
10. At resonance in a series LCR circuit:
- (A) Current is minimum
- (B) Impedance is maximum
- (C) Current is maximum
- (D) Power factor is zero
Answer: (C) Current is maximum
At resonance, inductive and capacitive reactances cancel, giving minimum impedance.
11. The refractive index of a medium depends primarily on:
- (A) Colour (wavelength) of light
- (B) Intensity of light
- (C) Size of the source
- (D) Distance travelled
Answer: (A) Colour (wavelength) of light
Refractive index varies with wavelength, causing dispersion.
12. In Young's double-slit experiment, fringe width increases if:
- (A) Slit separation increases
- (B) Screen distance increases
- (C) Wavelength decreases
- (D) Screen distance decreases
Answer: (B) Screen distance increases
Fringe width is directly proportional to the distance between the slits and the screen.
13. The power of a convex lens is +2 D. Its focal length is:
- (A) 0.5 m
- (B) 2 m
- (C) 1 m
- (D) 0.25 m
Answer: (A) 0.5 m
Power P = 1/f. Therefore, f = 1/2 = 0.5 m.
14. The phenomenon responsible for the blue colour of the sky is:
- (A) Reflection
- (B) Refraction
- (C) Scattering
- (D) Interference
Answer: (C) Scattering
Shorter wavelengths of sunlight are scattered more by atmospheric molecules.
15. The energy of a photon is directly proportional to its:
- (A) Wavelength
- (B) Frequency
- (C) Speed
- (D) Amplitude
Answer: (B) Frequency
Photon energy is given by E = hν.
16. The stopping potential in the photoelectric effect depends on:
- (A) Intensity of light
- (B) Frequency of incident light
- (C) Area of the metal surface
- (D) Distance from the source
Answer: (B) Frequency of incident light
Stopping potential depends on the maximum kinetic energy of emitted electrons, which depends on frequency.
17. In an intrinsic semiconductor, the number of electrons is:
- (A) Greater than holes
- (B) Less than holes
- (C) Equal to holes
- (D) Zero
Answer: (C) Equal to holes
An intrinsic semiconductor has equal numbers of electrons and holes.
18. A p-n junction diode conducts current easily when it is:
- (A) Reverse biased
- (B) Forward biased
- (C) Unbiased
- (D) Cooled
Answer: (B) Forward biased
Forward bias reduces the depletion layer, allowing current to flow.
19. Which logic gate produces an output of 1 only when both inputs are 1?
- (A) OR
- (B) NAND
- (C) AND
- (D) NOR
Answer: (C) AND
An AND gate gives a HIGH output only if all inputs are HIGH.
20. In electromagnetic waves, the electric field and magnetic field are:
- (A) Parallel to each other
- (B) Perpendicular to each other and to the direction of propagation
- (C) Parallel to the direction of propagation
- (D) Randomly oriented
Answer: (B) Perpendicular to each other and to the direction of propagation
Electromagnetic waves are transverse waves in which electric and magnetic fields are mutually perpendicular and also perpendicular to the direction of propagation.