What is electromagnetic radiation?

Electromagnetic radiation is the flow of energy at the speed of light through space or a material medium. This energy takes the form of electric and magnetic fields, creating electromagnetic waves like radio waves , visible light , and gamma rays . These waves have intensity and frequency, with the electric and magnetic fields linked at right angles, moving perpendicularly to the direction of motion. In quantum theory, electromagnetic radiation consists of photons, which are energy packets that always move at the speed of light. The spectrum of electromagnetic radiation ranges from low-frequency radio waves to high-frequency gamma rays . Electromagnetic radiation is produced when a charged particle changes its velocity, with the energy of the radiation coming from the charged particle.

What are some examples of electromagnetic radiation we encounter every day?

Electromagnetic radiation is everywhere, playing a vital role in both natural processes and modern technology. Examples of electromagnetic radiation we encounter daily: * Visible light enables sight, coming from the Sun and artificial lights. * Infrared radiation is felt as warmth from heaters and is emitted by almost every object. * Radio waves carry signals for TVs and radios. * Microwaves heat food in microwave ovens. * Ultraviolet radiation from the Sun can cause sunburn.

How does electromagnetic radiation travel through space?

Electromagnetic radiation travels through space as photons, which are packets of energy that move at the universal speed of light . In classical physics, electromagnetic radiation is the flow of energy through space in the form of electric and magnetic fields electromagnetic waves such as radio waves, visible light, and gamma rays. These waves are characterized by their intensity and frequency. A time-varying electric field produces a magnetic field, and vice versa, allowing electromagnetic radiation to propagate through space independently.

What is the electromagnetic spectrum and what does it include?

The electromagnetic spectrum is the complete range of electromagnetic radiation, categorized by frequency and wavelength. Electromagnetic radiation is a flow of energy at the speed of light, consisting of electric and magnetic fields. The electromagnetic spectrum includes: Radio waves Infrared radiation Visible light Ultraviolet radiation X-rays Gamma rays These categories differ in how the waves are emitted, transmitted, and absorbed. Spectroscopy uses nearly all frequencies and wavelengths of electromagnetic radiation.

How do the wavelength and frequency of electromagnetic waves relate to each other?

Electromagnetic waves have oscillating electric and magnetic fields that transfer energy through space at the speed of light. Wavelength ((\lambda)) is the distance between successive crests, while frequency ((\nu)) measures the wave's oscillations per second. The relationship between them is described by the equation (c = \lambda\nu), where c is the speed of light. Thus, wavelength and frequency are inversely proportional; high frequency means short wavelength, and vice versa.

How is electromagnetic radiation used in technologies like radios, microwaves, and X-rays?

Electromagnetic radiation, a form of energy that travels as oscillating electric and magnetic fields, is integral to various technologies. Radios use radio waves to transmit sound messages or information wirelessly through amplitude modulation (AM), frequency modulation (FM), or pulse modulation. Microwave ovens utilize microwave radiation to heat food. The microwaves, generated by a magnetron, cause water molecules in the food to vibrate, producing heat for cooking. X-rays are used in medical imaging to create contrasts of body parts based on the different scattering and absorption properties of bones and tissues. X-rays can also determine the identity and quantity of elements that compose a material. The electromagnetic spectrum includes a range of wavelengths and frequencies, from radio waves to gamma rays.

electromagnetic radiation

Introduction
General considerations
- Occurrence and importance
- The electromagnetic spectrum
- Generation of electromagnetic radiation
  - Continuous spectra of electromagnetic radiation
  - Discrete-frequency sources and absorbers of electromagnetic radiation
- Properties and behaviour
  - Scattering, reflection, and refraction
  - Superposition and interference
  - Propagation and coherence
  - Speed of electromagnetic radiation and the Doppler effect
- Cosmic background electromagnetic radiation
- Effect of gravitation
- The greenhouse effect of the atmosphere
Forms of electromagnetic radiation
- Radio waves
- Microwaves
- Infrared radiation
- Visible radiation
- Ultraviolet radiation
- X-rays
- Gamma rays
Historical survey
- Development of the classical radiation theory
  - Wave theory and corpuscular theory
  - Relation between electricity and magnetism
  - The electromagnetic wave and field concept
  - Speed of light
- Development of the quantum theory of radiation
  - Radiation laws and Planck’s light quanta
  - Photoelectric effect
  - Compton effect
  - Resonance absorption and recoil
  - Wave-particle duality
  - Quantum electrodynamics

References & Edit History Quick Facts & Related Topics

Images & Videos

Diagram of a tree leaf illustrating photosynthesis, with arrows showing sunlight, water, and carbon dioxide entering the leaf and sugars and oxygen being produced. A person is shown beside the tree to demonstrate the exchange of oxygen and carbon dioxide between plants and animals.

Diagram of the electromagnetic spectrum showing frequency, wavelength, and photon energy scales, with labeled regions for gamma rays, X-rays, ultraviolet, infrared, radar, microwaves, television, and radio waves. The visible light portion is highlighted and enlarged to the right, displaying its color range from violet to red.

Diagram of an electromagnetic wave showing two perpendicular oscillating fields: electric field (E) and magnetic field (B), both at right angles to the direction of wave propagation (c). Wavelength is marked as lambda.

Balmer series of hydrogen spectral lines

$Snell's law diagram showing an incident ray striking the boundary between media n1 and n2, reflecting at equal angle theta 1 and refracting toward the normal at angle theta 2.$

Diagram of a Michelson interferometer showing a laser beam split by a half-transparent mirror into two paths, reflected by a movable and a fixed mirror, and recombined to create an interference pattern on a screen.

Diagram illustrating the Doppler shift in astronomy, showing how absorption lines in a color spectrum move toward violet for approaching objects and toward red for receding objects, with labeled comparison spectra.

At a Glance

electromagnetic radiation summary

electromagnetic radiation

physics

Also known as: electromagnetic wave

Written by

Hellmut FritzscheAll

Fact-checked by

Britannica Editors

Last updated

Nov. 1, 2026 •History

Top Questions

What is electromagnetic radiation?
Electromagnetic radiation is the flow of energy at the speed of light through space or a material medium. This energy takes the form of electric and magnetic fields, creating electromagnetic waves like radio waves, visible light, and gamma rays. These waves have intensity and frequency, with the electric and magnetic fields linked at right angles, moving perpendicularly to the direction of motion.

In quantum theory, electromagnetic radiation consists of photons, which are energy packets that always move at the speed of light. The spectrum of electromagnetic radiation ranges from low-frequency radio waves to high-frequency gamma rays. Electromagnetic radiation is produced when a charged particle changes its velocity, with the energy of the radiation coming from the charged particle.
4 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
What are some examples of electromagnetic radiation we encounter every day?
Electromagnetic radiation is everywhere, playing a vital role in both natural processes and modern technology.

Examples of electromagnetic radiation we encounter daily:
* Visible light enables sight, coming from the Sun and artificial lights.
* Infrared radiation is felt as warmth from heaters and is emitted by almost every object.
* Radio waves carry signals for TVs and radios.
* Microwaves heat food in microwave ovens.
* Ultraviolet radiation from the Sun can cause sunburn.
3 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
How does electromagnetic radiation travel through space?
Electromagnetic radiation travels through space as photons, which are packets of energy that move at the universal speed of light. In classical physics, electromagnetic radiation is the flow of energy through space in the form of electric and magnetic fields electromagnetic waves such as radio waves, visible light, and gamma rays. These waves are characterized by their intensity and frequency. A time-varying electric field produces a magnetic field, and vice versa, allowing electromagnetic radiation to propagate through space independently.
2 Britannica Sources
1. electromagnetism: Interaction of a magnetic field with a charge
2. electromagnetic radiation
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
What is the electromagnetic spectrum and what does it include?
The electromagnetic spectrum is the complete range of electromagnetic radiation, categorized by frequency and wavelength. Electromagnetic radiation is a flow of energy at the speed of light, consisting of electric and magnetic fields.

The electromagnetic spectrum includes:
- Radio waves
- Infrared radiation
- Visible light
- Ultraviolet radiation
- X-rays
- Gamma rays
These categories differ in how the waves are emitted, transmitted, and absorbed. Spectroscopy uses nearly all frequencies and wavelengths of electromagnetic radiation.
4 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
How do the wavelength and frequency of electromagnetic waves relate to each other?
Electromagnetic waves have oscillating electric and magnetic fields that transfer energy through space at the speed of light.

Wavelength ((\lambda)) is the distance between successive crests, while frequency ((\nu)) measures the wave's oscillations per second. The relationship between them is described by the equation (c = \lambda\nu), where c is the speed of light.

Thus, wavelength and frequency are inversely proportional; high frequency means short wavelength, and vice versa.
3 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
How is electromagnetic radiation used in technologies like radios, microwaves, and X-rays?
Electromagnetic radiation, a form of energy that travels as oscillating electric and magnetic fields, is integral to various technologies.
- Radios use radio waves to transmit sound messages or information wirelessly through amplitude modulation (AM), frequency modulation (FM), or pulse modulation.
- Microwave ovens utilize microwave radiation to heat food. The microwaves, generated by a magnetron, cause water molecules in the food to vibrate, producing heat for cooking.
- X-rays are used in medical imaging to create contrasts of body parts based on the different scattering and absorption properties of bones and tissues. X-rays can also determine the identity and quantity of elements that compose a material. The electromagnetic spectrum includes a range of wavelengths and frequencies, from radio waves to gamma rays.
4 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

electromagnetic radiation, in classical physics, the flow of energy at the universal speed of light through free space or through a material medium in the form of the electric and magnetic fields that make up electromagnetic waves such as radio waves, visible light, and gamma rays. In such a wave, time-varying electric and magnetic fields are mutually linked with each other at right angles and perpendicular to the direction of motion. An electromagnetic wave is characterized by its intensity and the frequency ν of the time variation of the electric and magnetic fields.

In terms of the modern quantum theory, electromagnetic radiation is the flow of photons (also called light quanta) through space. Photons are packets of energy hν that always move with the universal speed of light. The symbol h is Planck’s constant, while the value of ν is the same as that of the frequency of the electromagnetic wave of classical theory. Photons having the same energy hν are all alike, and their number density corresponds to the intensity of the radiation. Electromagnetic radiation exhibits a multitude of phenomena as it interacts with charged particles in atoms, molecules, and larger objects of matter. These phenomena as well as the ways in which electromagnetic radiation is created and observed, the manner in which such radiation occurs in nature, and its technological uses depend on its frequency ν. The spectrum of frequencies of electromagnetic radiation extends from very low values over the range of radio waves, television waves, and microwaves to visible light and beyond to the substantially higher values of ultraviolet light, X-rays, and gamma rays.

The basic properties and behaviour of electromagnetic radiation are discussed in this article, as are its various forms, including their sources, distinguishing characteristics, and practical applications. The article also traces the development of both the classical and quantum theories of radiation.

General considerations

Occurrence and importance

Close to 0.01 percent of the mass/energy of the entire universe occurs in the form of electromagnetic radiation. All human life is immersed in it, and modern communications technology and medical services are particularly dependent on one or another of its forms. In fact, all living things on Earth depend on the electromagnetic radiation received from the Sun and on the transformation of solar energy by photosynthesis into plant life or by biosynthesis into zooplankton, the basic step in the food chain in oceans. The eyes of many animals, including those of humans, are adapted to be sensitive to and hence to see the most abundant part of the Sun’s electromagnetic radiation—namely, light, which comprises the visible portion of its wide range of frequencies. Green plants also have high sensitivity to the maximum intensity of solar electromagnetic radiation, which is absorbed by a substance called chlorophyll that is essential for plant growth via photosynthesis.

Practically all the fuels that modern society uses—gas, oil, and coal—are stored forms of energy received from the Sun as electromagnetic radiation millions of years ago. Only the energy from nuclear reactors does not originate from the Sun.

Italian-born physicist Dr. Enrico Fermi draws a diagram at a blackboard with mathematical equations. circa 1950.

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Physics and Natural Law

Everyday life is pervaded by artificially made electromagnetic radiation: food is heated in microwave ovens, airplanes are guided by radar waves, television sets receive electromagnetic waves transmitted by broadcasting stations, and infrared waves from heaters provide warmth. Infrared waves also are given off and received by automatic self-focusing cameras that electronically measure and set the correct distance to the object to be photographed. As soon as the Sun sets, incandescent or fluorescent lights are turned on to provide artificial illumination, and cities glow brightly with the colourful fluorescent and neon lamps of advertisement signs. Familiar too is ultraviolet radiation, which the eyes cannot see but whose effect is felt as pain from sunburn. Ultraviolet light represents a kind of electromagnetic radiation that can be harmful to life. Such is also true of X-rays, which are important in medicine as they allow physicians to observe the inner parts of the body but exposure to which should be kept to a minimum. Less familiar are gamma rays, which come from nuclear reactions and radioactive decay and are part of the harmful high-energy radiation of radioactive materials and nuclear weapons.

electromagnetic radiation

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General considerations

Occurrence and importance