13: Physical Constants
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The speed of light in free space (c), which is the phase velocity of any electromagnetic radiation in free space, is ≅2.9979×108 m/s. This is commonly rounded up to 3×108 m/s. This rounding incurs error of ≅0.07%, which is usually much less than other errors present in electrical engineering calculations.
The charge of an electron is ≅−1.602×10−19 C. The constant e≜+1.602176634×10−19 C is known as the “elementary charge,” so the charge of the electron is said to be −e.
The permittivity of free space (ϵ0) is ≅8.854×10−12 F/m.
The permeability of free space (μ0) is 4π×10−7 H/m.
The wave impedance of free space (η0) is the ratio of the magnitude of the electric field intensity to that of the magnetic field intensity in free space and is √μ0/ϵ0≅376.7 Ω. This is also sometimes referred to as the intrinsic impedance of free space.
Boltzmann’s constant is ≅1.381×10−23 J/K, the amount of energy associated with a change of one degree of temperature. This is typically assigned the symbol k (unfortunately, the same symbol often used to represent wavenumber).