• summary_type: concept
• word_count: 170

EM waves are transverse waves with E and B fields perpendicular to each other and to the direction of propagation. E and B are in phase (reach maxima simultaneously). The amplitude ratio E_0/B_0 = c = 3 x 10^8 m/s. Speed in vacuum: c = 1/sqrt(mu_0epsilon_0) — derived purely from electromagnetic constants, which Maxwell recognized as the speed of light. In a medium: v = c/n where n = sqrt(mu_repsilon_r). EM waves require no medium — they propagate through vacuum. They exhibit all wave phenomena: reflection, refraction, interference, diffraction, and polarization (being transverse). They are produced by accelerating charges — an oscillating charge at frequency f emits waves at frequency f. Stationary or uniformly moving charges do not radiate. The frequency of an EM wave is determined at the source and does not change when entering a medium; only the wavelength and speed change.