Radio waves and microwaves

Radio waves are produced by accelerated charges in conducting wires: rapid acceleration and deceleration of electrons in aerials. They are detected by receivers' aerials and used in radio and television communication.

Their usual range is roughly 500 kHz to 1000 MHz. AM (amplitude modulated) radio uses 530-1710 kHz; short-wave bands go up to 54 MHz; television uses 54-890 MHz; FM (frequency modulated) radio uses 88-108 MHz.

Cellular phones carry voice on radio waves in the ultrahigh frequency (UHF) band.

Microwaves are short-wavelength radio waves with frequencies in the gigahertz range, produced by special vacuum tubes (klystrons, magnetrons) and by Gunn diodes, and detected by point-contact diodes.

Their short wavelength suits them to radar for aircraft navigation. Radar is also the basis of the speed guns that time fast balls, tennis serves and vehicles.

In a microwave oven the frequency is chosen to match the resonant frequency of water molecules, so energy passes efficiently from the waves to the kinetic energy of the molecules and any food containing water gets hot.

With λ = c/ν: the FM band runs from 3 × 10⁸/88 × 10⁶ = 3.41 m down to 3 × 10⁸/108 × 10⁶ = 2.78 m, and 530 kHz on the AM band has λ = 566 m.