10th class Physics, Chapter 18: Electromagnetic Induction and Electromagnetic Waves MCQs

1. What happens to the induced e.m.f. in a coil if the rate of change of the magnetic field increases?

1. (A) Decreases
2. (B) Remains the same
3. (C) Increases ✓
4. (D) Becomes zero

2. In an A.C generator, slip rings are used to:

1. (A) reverse current direction periodically ✓
2. (B) convert A.C to D.C
3. (C) prevent induced current
4. (D) increase magnetic flux

3. The sky appears blue during the day due to:

1. (A) reflection of light
2. (B) scattering of shorter wavelengths ✓
3. (C) absorption of blue light
4. (D) refraction of light

4. Light can be considered as massless particles called:

1. (A) electrons
2. (B) protons
3. (C) photons ✓
4. (D) neutrons

5. In a transformer, energy is transferred from the primary coil to the secondary coil through:

1. (A) direct electrical connection
2. (B) a magnetic field in the iron core ✓
3. (C) electrons flowing through the core
4. (D) heat conduction

6. Electromagnetic induction was discovered in:

1. (A) 1785
2. (B) 1820
3. (C) 1905
4. (D) 1831 ✓

7. Electromagnetic induction is the process by which:

1. (A) a current produces heat
2. (B) a magnet is made by a battery
3. (C) light is produced from a magnet
4. (D) a changing magnetic field produces an electric current ✓

8. The induced current in a coil can be increased by:

1. (A) moving the magnet more slowly
2. (B) using a weaker magnet
3. (C) using a coil with more turns ✓
4. (D) using a coil with fewer turns

9. The SI unit of magnetic flux is:

1. (A) henry
2. (B) volt
3. (C) weber ✓
4. (D) tesla

10. The magnetic flux through a surface is maximum when the angle between B and the normal to the area is:

1. (A) 90°
2. (B) 45°
3. (C) 180° only
4. (D) 0° ✓

11. The magnetic flux through a surface is zero when the angle between B and the normal to the area is:

1. (A) 60°
2. (B) 90° ✓
3. (C) 0°
4. (D) 30°

12. According to Faraday's law, the induced e.m.f. is proportional to:

1. (A) the resistance of the coil
2. (B) the length of the wire only
3. (C) the temperature
4. (D) the rate of change of magnetic flux ✓

13. The negative sign in Faraday's law shows that:

1. (A) the e.m.f. is always negative
2. (B) the current is zero
3. (C) the flux decreases always
4. (D) the induced e.m.f. opposes the change producing it ✓

14. Lenz's law is a consequence of the law of conservation of:

1. (A) energy ✓
2. (B) momentum
3. (C) charge
4. (D) mass

15. An A.C. generator converts:

1. (A) electrical energy into mechanical energy
2. (B) chemical energy into electrical energy
3. (C) heat into mechanical energy
4. (D) mechanical energy into electrical energy ✓

16. The voltage in an A.C. generator reverses direction with every:

1. (A) half-turn of the coil ✓
2. (B) full turn of the coil
3. (C) two turns of the coil
4. (D) quarter-turn of the coil

17. In an A.C. generator the e.m.f. is maximum when the coil is:

1. (A) horizontal (parallel to the field) ✓
2. (B) vertical (perpendicular to the field)
3. (C) at rest
4. (D) in any position

18. The e.m.f. in an A.C. generator is zero when the coil is:

1. (A) vertical ✓
2. (B) horizontal
3. (C) at 90° to the vertical
4. (D) at 270°

19. The waveform of the e.m.f. of a simple A.C. generator is:

1. (A) a sine wave ✓
2. (B) a straight line
3. (C) a square wave
4. (D) a saw-tooth wave

20. The turns-ratio equation of a transformer is:

1. (A) Vₛ / Vₚ = Nₛ / Nₚ ✓
2. (B) Vₛ / Vₚ = Nₚ / Nₛ
3. (C) Vₛ × Vₚ = Nₛ × Nₚ
4. (D) Vₛ + Vₚ = Nₛ + Nₚ