Medium (optics)

Free space is the most simple and elementary electromagnetic medium. A medium is the stuff that waves propagate through. The properties, permittivity and permeability, define how electromagnetic waves travel through a medium. Also, the medium has an intrinsic impedance:

<math>\eta = \sqrt{\mu \over \varepsilon}<math>

where <math>\mu<math> is the permeability of the medium and <math>\varepsilon<math> is the permittivity of the medium.

Waves propagate through a medium with velocity of <math>c_w<math>. Simply the propagation velocity of a wave in a given medium is just the wavelength multiplied by its frequency, or its the angular frequency divided by the wavenumber(physics) or phase constant(electrical engineering).

<math>~ c_w = \nu \lambda ~<math>

<math> c_w = {\omega \over k} = {\omega \over \beta}<math>

The propagation velocity of electromagnetic waves in free space (medium) is

<math>c_w = {1 \over \sqrt{\varepsilon_0 \mu_0}}<math>

where, <math>~ \varepsilon_0 ~<math> is the vacuum permittivity of free space

<math>~ \mu_0 ~<math> is the vacuum permeability of free space.

See also: Electromagnetic spectrum, Electromagnetic radiation, Optics.