Radio waves are electromagnetic radiation with a wavelength longer than that of microwaves, but shorter than that of infrared light. In the electromagnetic spectrum, they occupy the part between microwaves and infrared waves. They are used in radar technology and for transmitting radio signals.
They were first predicted by Scottish mathematician James Clerk Maxwell in 1864 from his theory of electromagnetism. Maxwell discovered that self-propagating waves of electric and magnetic fields could exist. These fields oscillate at right angles to each other and to the direction of energy propagation. Since these oscillations occur at the speed of light, it follows that radio waves must also travel at the speed of light.
Maxwell’s equations predict that an antenna can be used to focus these self-propagating wave packets into a beam, just as a lens can be used to focus light waves. This led to the development of wireless communication using radio waves. The first practical application was developed by German physicist Heinrich Hertz in 1886, who showed that sparks could be produced across a gap by applying high voltages to metal plates using induction coils. Hertz’s work paved the way for further research into radio communications, leading eventually to today’s modern technologies such as mobile phones and satellite TV.
The term “radio wave” is actually somewhat misleading, since all electromagnetic radiation travels at the speed of light (300 million meters per second). However, radio waves are distinguished from other types of EM radiation by their wavelengths; specifically, they have wavelengths longer than those of microwaves but shorter than those of infrared radiation. In terms of frequency (which is related to wavelength), radio waves fall between 3 kilohertz (kHz) and 300 gigahertz (GHz).