• Tags: EM-wave, transverse, speed
• Difficulty: Moderate

EM waves are produced by accelerating charges. An oscillating charge of frequency f radiates EM waves of the same frequency. A stationary charge produces only a static E field; a charge moving at constant velocity produces static E and B fields but no radiation. Only acceleration produces EM radiation. Properties: (1) Transverse waves — E and B oscillate perpendicular to each other and to the propagation direction. (2) E and B are in phase — they reach maxima and zeros simultaneously. (3) $E_0$/$B_0$ = c always. (4) Speed in vacuum: c = 1/sqrt($mu_0$*$epsilon_0$) = 3 x 10^8 m/s — Maxwell computed this from purely electromagnetic constants and recognized it as the speed of light, unifying optics with electromagnetism. (5) No medium required — EM waves propagate through vacuum. (6) Obey superposition, interference, diffraction, and polarization (being transverse).