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Electromagnetic (EM) waves are the dynamic changes of electric and magnetic fields. They are produced whenever charged particles are accelerated, such as the electrons moving back and forth in an antenna. As the EM wave propagates along a certain direction, both electric and magnetic fields are perpendicular to the direction and to each other (Figure 8-1). In a vacuum, the EM wave travels at the speed of light, that is, 300,000,000 meters per second.

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Figure 8-1. The electromagnetic wave. [Source: OpenStax]

The wavelength (λ) of an EM wave is related to its frequency (f) by

λ = v / f

where v is the speed of the wave. Variation in wavelength (or frequency) gives rise to the electromagnetic spectrum which can be divided into radio waves, microwaves, infrared, visible light, ultraviolet, X-ray and gamma rays (Figure 8-2).

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Figure 8-2. The electromagnetic spectrum. Click here to enlarge. [Source: Wikipedia]