Close to 0.01 percent of the energy of the entire universe occurs in the form of electromagnetic radiation. All human life is immersed in it and modern communications technology and medical services are particularly dependent on one or another of its forms. In fact, all living things on Earth depend on the electromagnetic radiation received from the Sun. Our eyes are able to see most of the Sun’s electromagnetic radiation-namely light

Everyday life is pervaded by man-made electromagnetic radiation: food is heated in microwave ovens, airplanes are guided by radar waves, television sets receive electromagnetic waves transmitted by broadcasting stations.

What is an electromagnetic wave?

Electromagnetic radiation is the flow of energy through space at the universal speed of light, in the form of electric and magnetic fields that make up an electromagnetic wave. In this wave the electric and magnetic fields change their magnitude and direction each second. This rate of change or number of cycles per second is the frequency f of the wave measured in herz. The electric
and magnetic fields are always perpendicular to one another and at right angle to the direction of propagation. The wavelength is the distance between two adjacent troughs or two adjacent crests. Wavelength l and frequency f are related by the formula

c = lf,
where c is the speed of propagation of the wave. Then the smaller the frequency, the longer the wavelength

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Electromagnetic spectrum

Electromagnetic radiation spans an enormous range of frequencies or wavelengths as is shown by the electromagnetic spectrum. Going from the l values of radio waves to those of visible light is like comparing the thickness of a grain of sand with the distance of the Earth from the Sun, which represents an increasing factor of a million billion. Click here to view the Electromagnetic Spectrum.