Fact Check: Radio Wave

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. At 300 GHz, the corresponding wavelength is 1 mm (shorter than a grain of rice); at 30 Hz the corresponding wavelength is 10,000 km (6,200 mi) (longer than the radius of the Earth). Like all electromagnetic waves, radio waves in a vacuum travel at the speed of light, and in the Earth's atsmophere at a close, but slightly slower speed. Radio waves are generated by charged particles undergoing acceleration, such as varying electric currents. Naturally occuring 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 artificially by an electronic device called a transmitter, which is connected to an antenna which radiates the waves. They are received by another antenna connected to a radio receiver, which processes the received signal. Radio waves are very widely used in modern technology for fixed and mobile radio communication, broadcasting, radar and radio navigation systems, communications satellites, wireless computer networks, and many other applications. Different frequencies of radio waves have different propagation characteristics in the Earth's atmosphere; long waves can diffract around obstacles like mountains and follows the contour of the Earth (ground waves), shorter waves can reflect off ionosphere and return to Earth beyond the horizon (skywaves), while much shorter wavelengths bend or diffract very little and travel on the line of sight, so their propagation distances are limited to the visual horizon.

To prevent interference between different users, the artificial propagation and use of radio waves is strictly regulated by law, coordinated by an international body called the International Telecommunication Union (ITU), which defines radio waves as "electromagnetic waves of frequencies arbitrarily lower than 3,000 GHz, propagated in space without artificial guide." The radio spectrum is divided into a number of radio bands on the basis of frequencies, allocated to different users.

Radio waves were first predicted by the theory of electromagnetism proposed in 1867 by Scottish mathematical physicist James Clerk Maxwell. His mathematical theory, now called the Maxwell equations, predicted that a coupled electric and magnetic field could travel through space as "electromagnetic wave." Maxwell proposed that light consisted of electromagnetic waves of very short wavelength. In 1887, German physicist Heinrich Hertz demonstrated the reality of Maxwell's electromagnetic waves by experimentally generating radio waves in his laboratory, showing that they exhibited the same wave properties as light: standing wave, refraction, diffraction, and polarization. Italian inventor Guglielmo Marconi developed the first practical radio transmitters and receivers around 1894 - 1895. He received the 1909 Nobel Prize in Physics for his radio work. Radio communication began to be used commercially around 1900. The modern term "radio wave" replaced the original name Hertzian wave around 1912, while the standard unit of measurement was named after Heinrich Hertz.

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