Question

State and explain electromagnetic waves.

Answer 1

Electromagnetic waves

Electromagnetic waves are those waves in which there are sinusoidal variations of electric and magnetic fields at right angle to each other as well as at right angle to the direction of propagation of the waves.

e.g. visible light, U.V. rays, I.R. rays, X-rays, γ-rays microwaves, radio waves etc.

Production of electromagnetic waves

We know that a charge at rest can have only electric field around it. If the velocity of the charge is uniform, the magnetic field produced by it will also be uniform and hence no electromagnetic wave is produced. But if the charge is moving with accelerated motion both electric and magnetic fields will be changed and hence changing magnetic field will be produced, hence electromagnetic wave is produced. It means that only an accelerated charge emits electromagnetic waves, e.g. In an L-C circuit, the growth and decay of charge in the capacitor and growth and decay of magnetic field in the inductor L produce electromagnetic wave. In an atom, when an electron jumps from higher energy level to lower energy level, electromagnetic waves are produced.

1. When electric and magnetic fields vary along the direction perpendicular to each other, the energy propagates normal to their plane called electromagnetic wave.
2. No material medium is required for the propagation of electromagnetic waves i.e. they can travel in vacuum.
3. In free space (vacuum), velocity of electromagnetic waves is 3 x 10⁸ ms^-1.
4. Energy of electromagnetic wave is divided equally between electric and magnetic vectors.
5. The velocity of electromagnetic waves is independent of amplitude of electric and magnetic vectors and depends only on the electric and magnetic properties of the medium in which e.m. waves travel.
6. Velocity of electromagnetic wave decreases in a denser medium.
7. The electric vector is responsible for the optical effect of the wave and hence electric vector is called light vector.
8. Electric and magnetic fields are in the same phase, their values become zero and maximum at the same instant as shown in this figure.