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Physics LibreTexts

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 1.602×1019 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).


This page titled 13: Physical Constants is shared under a CC BY-SA license and was authored, remixed, and/or curated by Steven W. Ellingson (Virginia Tech Libraries' Open Education Initiative) .

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