Chapter 26.2, Problem 24SSC

To determine

To find: some of the primary characteristics of electromagnetic waves.

To explain: how EM waves differ from sound waves and other waves.

Answer to Problem 24SSC

A sound wave requires a medium to propagate but EM wave can travel through a vacuum as well as matter.

Explanation of Solution

Introduction:

Electromagnetic waves are also known as EM waves which are generated when an electric field comes into contact with the magnetic field. Electromagnetic waves can also be said to be the result of oscillating electric and magnetic fields. Electromagnetic waves are solutions of Maxwell's equations, which are the fundamental electrodynamics equations.

Since the EM wave is a combined electric and magnetic field that travels through space. EM waves travel with the speed of light i.e. $3.0\times {10}^8{\text{ms}}^{\text{-1}}$ . The wavelength and frequency of an EM wave can be related by the relation

  $\lambda =\frac{c}{f}$  ...... (1)

Here, $c$ and $f$ are speed of light and frequency of EM wave.

From equation (1), it is found that frequency and wavelength are inversely proportional to each other. This means long-wavelength electromagnetic wave has low frequency while short wavelength electromagnetic waves have a high frequency. EM waves, on the other hand, can propagate both through vacuum and matter. The speed of EM wave through a dielectric like air and glass is lower than that of the speed in a vacuum.

On the other hand, a sound wave requires a medium to propagate. The speed of such sound waves depends on the medium through which it passes. But EM waves can travel through a vacuum as well as matter.

Conclusion:

Hence, a sound wave requires a medium to propagate but EM wave can travel through a vacuum as well as matter.