Radio waves are produced by oscillations in an electrical circuit. In a transmitter, an alternating current makes electrons oscillate, which means they move rapidly backwards and forwards in the aerial. The oscillating electrons give out radio waves with the same frequency as the alternating current. For example, a current that alternates at 1000 kHz produces radio waves with a frequency of 1000 kHz. FM radio stations broadcast at frequencies of around 90 MHz.
The process also works in reverse. When radio waves are absorbed by a receiving aerial, their energy is transferred to the electrons in the metal, which makes them oscillate. This induces an alternating current in the receiving circuit, with the same frequency as the radio wave.
The receiving circuit can then process this current, for example to produce sound from a radio signal. Radio waves can therefore be produced by oscillations in a circuit and can themselves induce oscillations in a circuit.
