The speed of light in free space (\(c\)), which is the phase velocity of any electromagnetic radiation in free space, is \(\cong 2.9979 \times 10^8\) m/s. The wave impedance of free space (\(\eta_0\))...The speed of light in free space (\(c\)), which is the phase velocity of any electromagnetic radiation in free space, is \(\cong 2.9979 \times 10^8\) m/s. 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 \(\sqrt{\mu_0/\epsilon_0}\cong 376.7~\Omega\).
