characteristic impedance of vacuum
This constant is the characteristic impedance of a vacuum, the universal constant typically referenced as `Z_0`. It is also known as the impedance of free space or even more precisely as wave-impedance of a plane wave in free space.
This constant,`Z_0`, relates the magnitude of the electric field strength, |E|, to the magnitude of the magnetic field strength, |H|, for electromagnetic radiation traveling through a vacuum.
The constant `Z_0` is the product of two exactly-known constant values:
And thus the characteristic impedance of vacuum is exactly known