Visible light is only a small part of the electromagnetic spectrum. Any charges undergoing acceleration – this includes charges undergoing a change of direction at constant speed – generate electromagnetic fields and may result in the emission of electromagnetic radiation consisting of electric and magnetic fields at right angles to each other.
These oscillating fields sustain each other, propagating through space. No matter need be involved in this process so they may travel through a vacuum. The speed of electromagnet waves is given in terms of fundamental physical constants, and so is also constant atit is given the label c and is equal towhere
is the electric susceptibility of free space.
is the magnetic permeability of free space
The nature of electromagnetic waves is the same, but their origins may be very different, because of the vast range of energies involved. The whole electromagnetic spectrum can be divided into a series of subranges of frequencies or wavelengths, each with different properties.