Perpendicular oscillation of electric and magnetic components
An electromagnetic wave consists of two fields perpendicular to each other and both perpendicular to the direction of propagation. The electric field oscillates in one plane while the magnetic field oscillates in a perpendicular plane. They oscillate in phase, rising and falling together, with peaks and troughs occurring at the same locations along the wave path. This perpendicular arrangement is not arbitrary but emerges from Maxwell's equations: a changing electric field generates a magnetic field, and a changing magnetic field generates an electric field. Each field continuously regenerates the other, allowing the wave to propagate through empty space without requiring any medium.
Wave speed and the role of vacuum permittivity
The speed of electromagnetic waves in vacuum is determined entirely by two fundamental constants: the electric permittivity and magnetic permeability of space. The speed equals the reciprocal of the square root of their product, which calculates to approximately 300,000 kilometers per second. This speed is the same for all frequencies, meaning radio waves and gamma rays travel at identical velocities through empty space. When light enters a medium like glass or water, the effective speed decreases because the material's atoms absorb and reemit the wave, introducing delays. This slowdown causes refraction, bending light as it passes between materials, a principle essential to lenses, fiber optics, and optical instruments.