30 most important MCQs with answers on the topic of *electromagnetic waves* for Class 12 Physics exams
MCQs on Electromagnetic Waves
1. Electromagnetic waves are composed of:
- (a) Only electric fields
- (b) Only magnetic fields
- (c) Coupled electric and magnetic fields
- (d) Sound waves
- *Answer: (c) Coupled electric and magnetic fields
2. The speed of all electromagnetic waves in vacuum is:
- (a) 1.5 × 10⁸ m/s
- (b) 3 × 10⁸ m/s
- (c) 5 × 10⁶ m/s
- (d) 7 × 10⁹ m/s
- *Answer: (b) 3 × 10⁸ m/s
3. The only type of wave that does not require any medium to travel is:
- (a) Sound waves
- (b) Water waves
- (c) Electromagnetic waves
- (d) Seismic waves
- *Answer: (c) Electromagnetic waves
4. The transverse nature of electromagnetic waves means:
- (a) Electric and magnetic fields are parallel
- (b) Electric and magnetic fields are perpendicular to each other and the direction of propagation
- (c) Only electric field oscillates
- (d) They need a medium
- *Answer: (b) Perpendicular to each other and direction of propagation
5. Who predicted the existence of electromagnetic waves?
- (a) Faraday
- (b) Maxwell
- (c) Einstein
- (d) Hertz
- *Answer: (b) Maxwell
6. The energy of electromagnetic waves is carried by:
- (a) Electric field only
- (b) Magnetic field only
- (c) Both electric and magnetic fields
- (d) None
- *Answer: (c) Both electric and magnetic fields
7. The unit of wavelength is:
- (a) Hertz
- (b) Meter
- (c) Watt
- (d) Ampere
- *Answer: (b) Meter
8. Displacement current is due to:
- (a) Moving charges
- (b) Changing electric field
- (c) Stationary charges
- (d) Changing magnetic field
- *Answer: (b) Changing electric field
9. The electromagnetic wave with the longest wavelength is:
- (a) X-rays
- (b) Gamma rays
- (c) Radio waves
- (d) Ultraviolet rays
- *Answer: (c) Radio waves
10. In an electromagnetic wave, the electric and magnetic fields are always:
- (a) In phase
- (b) Out of phase
- (c) Independent
- (d) Constant
- *Answer: (a) In phase
12. What is the relationship between speed (c), wavelength (λ), and frequency (ν) of an EM wave?
- (a) c = λ /v
- (b) c = λ.v
- (c) c = 1/ λ.v
- (d) lambda = cv
- *Answer: (b) c = λ /v
13. Which of the following electromagnetic waves has the highest frequency?
- (a) X-rays
- (b) Radio waves
- (c) Ultraviolet rays
- (d) Gamma rays
- *Answer: (d) Gamma rays
14. The nature of electromagnetic waves is:
- (a) Longitudinal
- (b) Transverse
- (c) Both
- (d) None
- *Answer: (b) Transverse
15. In which medium do electromagnetic waves travel with maximum speed?
- (a) Air
- (b) Water
- (c) Glass
- (d) Vacuum
- *Answer: (d) Vacuum
16. The ratio of amplitudes of electric and magnetic fields in a vacuum is:
- (a) 1:1
- (b) c:1
- (c) 1:c
- (d) ε₀:µ₀
- *Answer: (b) c:1
17. Which electromagnetic wave is used in television remote controls?
- (a) Ultraviolet
- (b) Infrared
- (c) Radio waves
- (d) Gamma rays
- *Answer: (b) Infrared
18. Visible light forms a part of:
- (a) Ultrasound spectrum
- (b) Electromagnetic spectrum
- (c) Mechanical wave spectrum
- (d) Sound spectrum
- *Answer: (b) Electromagnetic spectrum
19. The electromagnetic spectrum does NOT contain:
- (a) Microwaves
- (b) Infrared rays
- (c) Sound waves
- (d) Gamma rays
- *Answer: (c) Sound waves
20. Maxwell’s equations predicted:
- (a) Sound waves
- (b) Electromagnetic waves
- (c) Water waves
- (d) Matter waves
- *Answer: (b) Electromagnetic waves
21. The wavelength of visible light is approximately:
- (a) 400–700 nm
- (b) 1–10 cm
- (c) >1 m
- (d) <10 nm
- *Answer: (a) 400–700 nm
22. The magnetic field amplitude (B_0) and electric field amplitude (E_0) are related as:
- (a) E_0 = cB_0
- (b) E_0 = B_0/c
- (c) B_0 = E_0 c
- (d) None
- *Answer: (a) E_0 = cB_0
23. The part of the electromagnetic spectrum with frequency just lower than visible light is:
- (a) Ultraviolet
- (b) X-rays
- (c) Infrared
- (d) Radio waves
- *Answer: (c) Infrared
24. The energy flow per unit area per unit time in an electromagnetic wave is called:
- (a) Intensity
- (b) Energy density
- (c) Poynting vector
- (d) Amplitude
- *Answer: (c) Poynting vector
25. Unit of displacement current is:
- (a) Coulomb
- (b) Ampere
- (c) Farad
- (d) Volt
- *Answer: (b) Ampere
26. The person who experimentally confirmed electromagnetic waves:
- (a) Hertz
- (b) Maxwell
- (c) Ampere
- (d) Gauss
- *Answer: (a) Hertz
27. Which EM wave has a frequency just higher than ultraviolet?
- (a) Infrared
- (b) X-rays
- (c) Microwave
- (d) Radio waves
- *Answer: (b) X-rays
28. The electric and magnetic fields in an EM wave are:
- (a) Parallel and in phase
- (b) Perpendicular and in phase
- (c) Perpendicular and out of phase
- (d) Parallel and out of phase
- *Answer: (b) Perpendicular and in phase
29. Which part of the EM spectrum is used for sterilizing surgical instruments?
- (a) Infrared
- (b) Ultraviolet
- (c) Microwaves
- (d) Gamma rays
- *Answer: (b) Ultraviolet
30. The use of microwaves is in:
- (a) Ovens and radar
- (b) Sterilization
- (c) X-ray tubes
- (d) Photosynthesis
- *Answer: (a) Ovens and radar
