Radio wave

Radio wave is a type of electromagnetic radiation with wavelengths in the electromagnetic spectrum longer than infrared light. Radio waves have frequencies from 300 GHz to as low as 3 kHz, and corresponding wavelengths from 1 millimeter to 100 kilometers.

Like all other electromagnetic waves, radio waves travel at the speed of light in vacuum. They are generated by electric charges undergoing acceleration, such as time varying electric currents. Naturally occurring radio waves are emitted by lightning and astronomical objects, or are caused by random processes in plasma.

History

The existence of radio waves was predicted by James Clerk Maxwell in 1864 from his equations. In 1888, Heinrich Hertz demonstrated that these waves could be transmitted through the air at different speeds and that they could be reflected and refracted like light.

Uses

Radio waves are used for wireless transmission of sound messages, or information, such as in mobile phones, television, and radio. This is achieved by superposing (modulating) the information to be sent on the radio wave (carrier wave) of a specific frequency, then broadcasting the resulting signal through an antenna.

Propagation

Radio waves can be absorbed and reflected by the atmosphere, ionosphere, and the earth's surface. At night, absorption decreases and reflection increases, both effects that enhance the transmission of radio signals over long distances.

See also

• Electromagnetic spectrum
• Radio frequency
• Wireless communication

References

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Radio wave

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  Dipole transmitting antenna animation
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  Radio waves
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  Dipole receiving antenna animation
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  Radio waves hazard symbol