Electromagnectic Radiation

Electromagnetic radiation (often abbreviated in EM) consists of oscillating electric and magnetic fields. Electromagnetic radiation is a wave that propagates, in vacuum, with the speed of light,
c=300,000 Km/sec. Contrary to sound waves, which are longitudinal, EM waves are transverse, which means the electric and magnetic fields are perpendicular to the direction of propagation of the wave.

A simple sinusoidal wave is characterized by its wavelength l (lambda), which is the length between two consecutive crests, and its frequency n (nu), which is the number of oscillations per seconds. l and n are related to c in the following way:

c = l n ,

if we want to get n from l and c, then

n = c /l ,

if we want to get l from n and c, then

l = c / n .

A photon can have an arbitrary large value of its frequency, as well as an arbitrary small one. There is no minimum or maximum frequency, and same holds for the wavelength, of course. Visible light is composed of photons within a certain values of frequencies (and wavelengths). Specifically, light visible to human eyes has wavelengths between 4,000 Angstrom (1 Angstrom is 10^-8 cm) (this is red light) and 7,000 Angstrom (this is violet light). It should be clear that there are no sharp boundaries indeed electromagnetism (the study of electromagnetic phenomena) is very democratic and all electromagnetic waves have the same properties, except for different values of wavelengths.(Bear in mind that, since c = l n wavelength and frequency are related, where c, the speed of light, is a physical constant; thus if the wavelength changes, so does the frequency in order to keep the product the same).