Electromagnetic Waves

Unlike mechanical waves, EM waves require no material medium and can travel through a vacuum at the absolute speed of light (c \approx 3 \times 10^8 \text{ m/s}). Maxwell’s crucial theoretical contribution was the introduction of displacement current, which bridged a missing gap in Ampere's law and proved that a changing electric field produces a magnetic field just as a physical current does.

The complete range of these waves is classified by frequency and wavelength in the Electromagnetic Spectrum. This spectrum spans from long radio waves used in communications, through microwaves, infrared, visible light, and ultraviolet, up to highly energetic X-rays and gamma rays, forming the basis for almost all modern wireless technology and remote sensing.