Electromagnetic waves are transverse in nature.
They consist of electric (E) and magnetic fields (B) oscillating at right angles to each other and perpendicular to the direction of propagation (k).
They propagate through free space (in vacuum) with a uniform velocity.
v = 3 × 108 ms–1 = c (velocity of light)
For a medium of permeability µ (= µ0.µr) and permittivity ε (= ε0.εr) the velocity becomes
v = 1/(√µε)
The nature and action of these waves depends on their frequency (or wavelength).
Maxwell’s theory placed no restriction on possible wavelengths for e.m. waves and hence e.m. waves of wavelengths ranging from 6 × 10–13 m have been successfully produced.
There is no limit to very long wavelengths which correspond to radio broadcast waves. The whole range of e.m. waves from very long to very short wavelengths constitutes the electromagnetic spectrum.