30 most important MCQs with answers on the topics of Electromagnetic Induction and Alternating Current for Class 12 Physics exams:
MCQs on Electromagnetic Induction
1. Whenever the magnetic flux linked with an electric circuit changes, an emf is induced in the circuit. This is called
(a) Electromagnetic induction
(b) Lenz's law
(c) Hysteresis loss
(d) Kirchhoff's law
*Answer: (a) Electromagnetic induction*
2. The emf induced in a coil is proportional to:
(a) Rate of change of magnetic flux
(b) Resistance of coil
(c) Coil temperature
(d) None of these
*Answer: (a) Rate of change of magnetic flux*
3. According to Faraday's law, an electric field is produced by:
(a) Time varying magnetic flux
(b) Time varying electric flux
(c) Moving charges
(d) Stationary magnetic field
*Answer: (a) Time varying magnetic flux*
4. Lenz’s law helps to determine:
(a) Magnitude of induced emf
(b) Direction of induced emf
(c) Energy of magnetic field
(d) None of these
*Answer: (b) Direction of induced emf*
5. The unit of magnetic flux is:
(a) Tesla
(b) Weber
(c) Henry
(d) Volt
*Answer: (b) Weber*
6. Induced emf opposes the change in magnetic flux due to:
(a) Coulomb's law
(b) Ohm's law
(c) Lenz’s law
(d) Ampere's law
*Answer: (c) Lenz’s law*
7. The quantity $$ N \times \frac{d\Phi}{dt} $$ represents:
(a) Resistance
(b) Induced emf
(c) Magnetic field
(d) Electric current
*Answer: (b) Induced emf*
8. The emf induced in a coil when the magnetic flux changes by 0.05 Wb/s and number of turns is 50 is:
(a) 2.5 V
(b) 0.05 V
(c) 50 V
(d) 100 V
*Answer: (a) 2.5 V*
9. A coil connected to a galvanometer shows deflection when:
(a) Magnetic flux remains constant
(b) Flux varies with time
(c) Coil is stationary
(d) None of these
*Answer: (b) Flux varies with time*
10. The phenomenon of induced currents in a conductor moving in a magnetic field is called:
(a) Eddy current
(b) Static electricity
(c) Thermoelectric effect
(d) None of these
*Answer: (a) Eddy current*
MCQs on Alternating Current
11. The rms value of an alternating current is:
(a) Maximum value of current
(b) Average value of current
(c) Value of direct current producing the same heating effect
(d) Zero
*Answer: (c) Value of direct current producing the same heating effect*
12. The frequency of standard AC in India is:
(a) 25 Hz
(b) 50 Hz
(c) 60 Hz
(d) 100 Hz
*Answer: (b) 50 Hz*
16. The power factor in a pure resistive circuit is:
(a) 0
(b) 1
(c) 0.5
(d) None
*Answer: (b) 1*
17. The phase difference between voltage and current in a pure inductive circuit is:
(a) 0°
(b) 45°
(c) 90°
(d) 180°
*Answer: (c) 90°*
19. The unit of inductive reactance is:
(a) Ohm
(b) Henry
(c) Tesla
(d) Weber
*Answer: (a) Ohm*
20. Transformer works on the principle of:
(a) Electromagnetic induction
(b) Ohm’s law
(c) Conservation of energy
(d) Kirchhoff’s law
*Answer: (a) Electromagnetic induction*
21. The ratio of secondary to primary voltage in an ideal transformer is equal to:
(a) Number of secondary turns / Number of primary turns
(b) Number of primary turns / Number of secondary turns
(c) Current ratio
(d) None
*Answer: (a) Number of secondary turns / Number of primary turns*
23. The frequency of AC supplied to houses in India is:
(a) 50 Hz
(b) 60 Hz
(c) 100 Hz
(d) 25 Hz
*Answer: (a) 50 Hz*
24. The main loss in transformer is due to:
(a) Hysteresis and eddy current losses
(b) Resistance of coil
(c) Leakage flux
(d) None
*Answer: (a) Hysteresis and eddy current losses*
25. An inductor in an AC circuit causes:
(a) Current to lag voltage by 90°
(b) Voltage to lag current by 90°
(c) No phase difference
(d) Power factor = 0
*Answer: (a) Current to lag voltage by 90°*
27. The current in a purely capacitive AC circuit:
(a) Lags voltage by 90°
(b) Leads voltage by 90°
(c) Is in phase with voltage
(d) Zero
*Answer: (b) Leads voltage by 90°*
28. The transformer is a device which:
(a) Changes voltage level
(b) Changes frequency
(c) Changes power supplied
(d) All of these
*Answer: (a) Changes voltage level*
29. The inductance of a coil depends on:
(a) Number of turns
(b) Area of cross section
(c) Length of coil
(d) All of these
*Answer: (d) All of these*
30. The effect of AC in heating a resistor is:
(a) Same as DC of equal RMS value
(b) More than DC
(c) Less than DC
(d) Zero
*Answer: (a) Same as DC of equal RMS value*
