Characteristic impedance of the vacuum
|Surname||Characteristic impedance of the vacuum|
|Size type||Electrical resistance|
|SI||3.767 303 136 67 (57)e2|
|Relation to other constants|
Magnetic field constant speed of light
The wave resistance of the vacuum , also free space wave resistance , field wave resistance of the vacuum or wave impedance of the vacuum , is a physical constant with the unit ohm . The free space wave resistance indicates the relationship between the amounts of the electric field strength and the magnetic field strength of an electromagnetic wave that propagates in a vacuum , i.e.:
In the International System of Units (SI) the value is
Relationship with other fundamental constants
The wave resistance of the vacuum can be calculated from other natural constants:
Are in it
- the magnetic field constant
- the speed of light
- the electric field constant
- the Planck constant
- the fine structure constant
- the elementary charge .
Until the redefinition of the SI units in 2019 , the numerical values of the constants and the definition of the units “meter” and “ampere” were precisely defined. This had the exact value of . Since May 20, 2019, the numerical value is still exact, but no longer. The numerical value of the product is therefore subject to the same relative measurement uncertainty (1.5 × 10 −10 ) as that of .
Characteristic impedance in a medium
The relative permittivity of air under normal conditions is approximately , its permeability number is only slightly higher than 1. The wave resistance of the atmosphere is approximately well reduced compared to the wave resistance of the vacuum .
- Gerthsen physics . , Dieter Meschede , 23rd edition, Springer-Verlag, Berlin / Heidelberg / New York 2006, ISBN 978-3-540-25421-8 , p. 427.
- CODATA Recommended Values. NIST , accessed July 7, 2019 (value for the magnetic field constant).
- CODATA Recommended Values. NIST , accessed July 7, 2019 (value for the speed of light).
- Otto Zinke, Heinrich Brunswig, Anton Vlcek: High frequency technology: high frequency filters, lines, antennas, Volume 1