Naturally occurring radio waves are emitted by lightning and astronomical objects, and are part of the blackbody radiation emitted by all warm objects. Radio waves are generated by charged particles undergoing acceleration, such as time-varying electric currents. Like all electromagnetic waves, radio waves in a vacuum travel at the speed of light, and in the Earth's atmosphere at a close, but slightly lower speed. At 300 GHz, the corresponding wavelength is 1 mm (shorter than a grain of rice) at 30 Hz the corresponding wavelength is 10,000 kilometers (6,200 miles) (longer than the radius of the Earth). Radio waves are a type of electromagnetic radiation with the longest wavelengths in the electromagnetic spectrum, typically with frequencies of 300 gigahertz ( GHz) and below.
In this animation the action is shown slowed down enormously.
Loops of electric field leave the antenna and travel away at the speed of light these are the radio waves. The transmitter applies an alternating electric current to the rods, which charges them alternately positive (+) and negative (−). The antenna in the center is two vertical metal rods connected to a radio transmitter (not shown). Animation of a half-wave dipole antenna radiating radio waves, showing the electric field lines.
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