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\triangleq +1.602176634 \times 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 (\epsilon_0) is \cong 8.854 \times 10^{-12} F/m.
The permeability of free space (\mu_0) is 4\pi \times 10^{-7} H/m.
The wave impedance of free space (\eta_0) is the ratio of the magnitude of the electric field intensity to that of the magnetic field intensity in free space and is \sqrt{\mu_0/\epsilon_0}\cong 376.7~\Omega. This is also sometimes referred to as the intrinsic impedance of free space.
Boltzmann’s constant is \cong 1.381 \times 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).