Physical Constants

The speed of light in free space (

), which is the phase velocity of any electromagnetic radiation in free space, is

m/s. This is commonly rounded up to

m/s. This rounding incurs error of

%, which is usually much less than other errors present in electrical engineering calculations.

The charge of an electron is

C. The constant

C is known as the “elementary charge,” so the charge of the electron is said to be


The permittivity of free space (

) is


The permeability of free space (



The wave impedance of free space (

) is the ratio of the magnitude of the electric field intensity to that of the magnetic field intensity in free space and is

. This is also sometimes referred to as the intrinsic impedance of free space.


Ellingson, Steven W. (2018) Electromagnetics, Vol. 1. Blacksburg, VA: VT Publishing. CC BY-SA 4.0

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