The Electromagnetic Spectrum

The electromagnetic spectrum is the range of frequencies and corresponding wavelengths of electromagnetic radiation.

Wavelength and frequency are inversely proportional to each other; the longer the wavelength, the lower the frequency.

The energy of electromagnetic radiation is directly proportional to its frequency, as shown by Planck’s equation. Thus, the highest-energy electromagnetic waves have the shortest wavelengths.

Electromagnetic waves are categorized as radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, or gamma rays depending on their frequencies and wavelengths.

Radio waves, which are used to transmit signals between communications systems, have the longest wavelengths, the lowest frequencies, and the least amount of energy.

Microwaves have the next longest wavelengths. Their uses range from radar systems to heating food at home.

Next is infrared radiation, which is a significant part of the thermal radiation emitted by warm objects. For example, Earth both absorbs infrared radiation as part of the radiant energy emitted by the sun and itself emits infrared radiation into space.

The wavelengths of visible light are shorter still, ranging from 740 to 390 nanometers. Red light has the longest wavelengths, and violet has the shortest. Human eyes are only responsive to this narrow wavelength range.

Ultraviolet radiation has yet shorter wavelengths. Sunlight is the most familiar source of ultraviolet radiation, which has enough energy that excessive exposure causes sunburns and leads to skin cancer.

X-rays and gamma rays have the shortest wavelengths and are the most energetic forms of electromagnetic radiation. X-rays can pass through many substances, but they do not pass through bones very easily. This makes them an important imaging tool.

Gamma rays are best known as being released during the decay chains of certain radioactive elements. While there is no universal distinction between gamma and X-rays, gamma rays are typically considered to have the shortest wavelengths, highest frequencies, and highest energies.