# Conceptual Questions Based on Class 12 Physics Electromagnetic Waves

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Here we are providing conceptual questions based on class 12 physics chapter 8 electromagnetic waves. These questions are prepared by experts and are very useful from exam point of view. Students can practice these questions for scoring better marks in the exam.

## Conceptual Questions Based on Class 12 Physics Electromagnetic Waves

Q.1. What is displacement current due to?

Solution. Displacement current exists due to a time-varying electric field or changing electric flux.

Solution. No, displacement current also produces a magnetic field between the capacitor plates.

Q.3. What evidence is there that sound is not electromagnetic in nature?

Solution. Sound waves require an inertial medium for their propagation which shows that sound waves are mechanical in nature and not electromagnetic.

Q.4. What does an electromagnetic wave consist of? On what factors does its velocity in vacuum depend?

Solution. An electromagnetic wave consists of electric and magnetic fields, oscillating sinusoidally both in time and space. The two fields are perpendicular to each other as well as to the direction of propagation of the wave.

The velocity of an e.m. wave in vacuum depends on its performability (μ0) and permittivity (ε0).

Q.5. What oscillates in electromagnetic waves? Are these waves transverse or longitudinal?

Solution, (i) In e.m. waves, electric and magnetic fields oscillate in mutually perpendicular directions.

(ii) These waves are transverse in nature.

Q.6. A capacitor of capacitance C, is being charged up by connecting it across a d.c. voltage source of voltage V. How do the conduction and displacement currents, in this set-up compare with each other

(a) during the charging up process?

(b) after the capacitor gets fully charged?

Solution. By the property of continuity,

(a) Conduction current

= Displacement current

= a non-zero value, during the charging up process.

(b) Conduction current

= Displacement current

= 0, after the capacitor gets fully charged.

Q.7. If you find closed loops of B in a region in space, does it necessarily mean that actual charges are flowing across the area bounded by the loops?

Solution. Not necessarily. A displacement current (such as that between the plates of a capacitor that is being charged) can also produce loops of B, where charges do not flow actually.

Q.8. What feature of electromagnetic waves led Maxwell to conclude that light itself is an electromagnetic wave?

Solution. The emergence of the speed of light from purely electromagnetic consideration led Maxwell to conclude that light waves are electromagnetic in nature.

Q.9. What is the ratio of speed of infrared and ultraviolet rays in vacuum?

Solution. Ratio = 1, because the speed of an electromagnetic wave in vacuum is independent of its wavelength or frequency.

Q.10. Out of microwaves, ultraviolet rays and infra-red rays, which radiation will be most effective for emission of electrons from a metallic surface.

Solution. Ultraviolet rays are most effective for photoelectric emission because they have highest frequency and hence most energetic.

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