Electromagnetic wave

An electromagnetic wave is a self-propelling ripple of electric and magnetic fields that surfs through empty space at the speed of light, carrying energy from one place to another with no wire and no medium required. Picture two dancers, E and B, holding hands and spinning at right angles to each other: as the electric field rises and falls, it creates the magnetic field, and as the magnetic field rises and falls, it re-creates the electric field. Each one keeps the other alive, so the pair sails forward forever — the field equivalent of a perpetual relay race.

The whole zoo of light is just EM waves of different wavelengths: radio waves metres long, microwaves a few centimetres, the visible rainbow at half a micron, then ultraviolet, X-rays, and gamma rays shrinking toward the size of an atom. All of them travel at exactly c ≈ 300,000 km/s in vacuum. A wave's frequency and wavelength multiply to give that fixed speed, so a 2.4 GHz Wi-Fi signal has a wavelength of about 12.5 cm — small enough to fit antennas inside your laptop, large enough to bend around furniture and reach the next room.