Impedance of free space

The characteristic impedance of the vacuum, also free space wave impedance or characteristic impedance of vacuum or wave impedance of the vacuum is a physical constant. It indicates the ratio between the amounts of the electric field and the magnetic field strength of a propagating electromagnetic wave in a vacuum. In the SI system it carries the units of ohms. Their value is

Context of other fundamental constants

The characteristic impedance of the vacuum can be calculated from other constants of nature. Are the magnetic field constant and the electric field constant or either in combination with the speed of light. Since the value of this constant is determined as part of the SI system to exact values ​​can be calculated with any degree of accuracy. He is:

Or

Wave impedance

The propagation of electromagnetic waves in a ( dielectric ) medium of the wave impedance of the permeability and permittivity of the medium depends on:

The dielectric constant of air under normal conditions is about, the relative permeability of air is only slightly larger than 1, the wave impedance in air is due to the permittivity of the surrounding atmosphere to well reduced compared to the characteristic impedance of the vacuum. He is about.