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
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.