Characteristic impedance of the vacuum
Physical constant | |
---|---|
Surname | Characteristic impedance of the vacuum |
Formula symbol | |
Size type | Electrical resistance |
value | |
SI | 3.767 303 136 67 (57)e2 |
Uncertainty (rel.) | 1.5e-10 |
Planck units | |
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
When electromagnetic waves propagate in a dielectric medium , the wave resistance depends on the permeability and permittivity of the 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 .
literature
- Gerthsen physics . , Dieter Meschede , 23rd edition, Springer-Verlag, Berlin / Heidelberg / New York 2006, ISBN 978-3-540-25421-8 , p. 427.
Individual evidence
- ↑ 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