Electromagnetic Waves Class 12 MCQ Questions: Electromagnetism centers on the combination of electric and magnetic fields. Electric currents generate magnetic fields, and current-carrying wires interact magnetically. Upon exploring how changing magnetic fields induce electric fields, one must question whether changing electric fields also produce magnetic fields? Maxwell confirmed that varying electric fields generate magnetic fields. However, an inconsistency arose with Ampere’s law applied to a changing current in a capacitor, leading Maxwell to introduce the “displacement current” for consistency. Maxwell’s equations, uniting electric and magnetic fields from charges and currents, form the foundation of electromagnetism alongside the Lorentz force formula. An important prediction of Maxwell’s equations is electromagnetic waves—dynamic blends of electric and magnetic fields moving through space. Their speed matches light’s, confirming light as an electromagnetic wave. Maxwell unified electricity, magnetism, and light. Hertz’s confirmation of these waves led to their use by innovators like Marconi, revolutionising communication. This chapter emphasises the “displacement current” and its implications, then explores electromagnetic wave complexities, spanning gamma rays to radio waves, composing the electromagnetic spectrum.
Electromagnetic Waves Class 12 MCQ Questions with Answers
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1 ________ has minimum wavelength?
(a) Blue light
(b) gamma-rays
(c) infrared rays
(d) microwave
Answer: (b)
2 When electromagnetic waves enter the ionised layer of ionosphere, then the relative permittivity i. e. dielectric constant of the ionised layer
(a) does not change
(b) appears to increase
(c) appears to decrease
(d) sometimes appears to increase and sometimes to decrease
Ans: (c)
3 Which of the following has maximum penetrating power?
(a) Ultraviolet radiation
(b) Microwaves
(c) γ-rays
(d) Radio waves
Answer: (c)
4 Displacement current is always
(a) equal to conduction current
(b) less than conduction current
(c) greater than conduction current
(d) the sum of current due to flow of positive and negative ions
Answer: (a)
5 Waves in decreasing order of their wavelength are
(a) radio waves, ultraviolet rays, visible rays, X-rays
(b) radio waves, visible rays, infrared rays, X-rays
(c) radio waves, infrared rays, visible rays, X-rays
(d) X-rays, infrared rays, visible rays, radio waves
Answer: (c)
6 Name the law which states that a varying electric field produces a magnetic field:
- Biot-Savart’s law
- Faraday’s law
- Modified Ampere’s law
- None of these
Answer: (c)
7 ______ waves used by artificial satellites for communication
(a) micro
(b) infrared waves
(c) radio waves
(d) X-rays
Answer: (a)
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