Electromagnetic Radiation Explained

Nicholas Amendolare, Scott van Tonningen
  • Author
    Nicholas Amendolare

    Nicholas Amendolare is a high school and middle school science teacher from Plymouth, Massachusetts. He has a bachelor's degree in environmental science from Worcester Polytechnic Institute and a master's degree in education from Harvard University. He has been a teacher for nine years, has written for TED-Ed, and is the founder of

  • Instructor
    Scott van Tonningen

    Scott has a Ph.D. in electrical engineering and has taught a variety of college-level engineering, math and science courses.

Understand what electromagnetic radiation is by learning its definition. Learn how are the wavelength and frequency of electromagnetic radiation are related. Updated: 09/28/2021

Table of Contents


What is Electromagnetic Radiation?

Electromagnetic radiation is the propagation of energy, in the form of light, through space. Much like ocean waves transfer energy through water, electromagnetic waves transfer energy through an electromagnetic field. Electromagnetic radiation travels in packets of energy called photons, and the energy in each photon depends upon the wave's frequency (but not amplitude). The radiation is created by the motion of charged particles and includes seven types: including radio waves, microwaves, infrared light, visible light, ultraviolet light, X-rays, and gamma rays. It is important to note that visible light is not fundamentally different from the other six types, except for the fact that it can be detected by the human eye.

What is Electromagnetic Energy?

Electromagnetic energy is simply the energy carried by electromagnetic waves often referred to as electromagnetic radiation. The energy travels at the speed of light (in fact, it is light!) in a vacuum, but travels slower through a medium. It can be emitted from objects, reflected by objects, or absorbed by objects. In the case of emission, the motion of charged particles within an object typically creates the wave (imagine the hot filament in a lightbulb). In the case of reflection, the wave bounces off a surface (imagine a mirror). And in the case of absorption, the wave is absorbed by an object and the charged particles within the object begin to move faster (imagine pavement absorbing sunlight on a hot day).

Electromagnetic Spectrum

Like any wave, electromagnetic energy can be measured. The speed of its oscillation is called "frequency" and the lengths of the individual waves, measured from crest to crest, are called "wavelengths." Scientists have categorized the types of light, according to frequency and wavelength, into something called the electromagnetic spectrum. Electromagnetic radiation can range from wavelengths of several meters (radio waves) to wavelengths of picometres (gamma rays). The frequencies can range from hundreds of billions of Hertz (radio waves) all the way up to several septillion Hertz (gamma rays). As one travels up the spectrum, from low frequency to high frequency, the energy of each individual photon increases. This is why radio waves are considered harmless and X-rays and gamma rays are very dangerous. Photon energy is measured in electron volts, and it ranges from billionths of electron volts (radio waves) to millions of electron volts (gamma rays).

A NASA diagram of the electromagnetic spectrum.

The elctromagnetic spectrum

Altogether, the electromagnetic spectrum can be ranked from low-frequency, low-energy, high wavelength all the way up to high-frequency, high-energy, low-wavelength. This ranking includes seven categories, listed in order as follows:

  • radio waves
  • microwaves
  • infrared light
  • visible light
  • ultraviolet light
  • X-rays
  • gamma rays

As you might have guessed, radio waves and microwaves have the least energy and are the least dangerous for humans. Meanwhile, X-rays and gamma rays have the most energy and can even cause cancer in humans.

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  • 0:01 Introduction to EM Radiation
  • 1:36 Definition of EM Radiation
  • 3:19 Return to First Example
  • 4:13 Electromagnetic Spectrum
  • 4:38 EM Radiation & Energy
  • 7:10 Lesson Summary
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How are the Wavelength and Frequency of Electromagnetic Radiation Related?

The two main properties that we use to categorize electrogenic radiation, the frequency of electromagnetic radiation and the electromagnetic radiation wavelength, are inverse. Because the speed of light is constant, a higher frequency will always mean a shorter wavelength and a higher wavelength will always mean a lower frequency.

Frequency can be defined as the number of waves that travel past a point each second. And wavelength can be defined as the length of a wave, measured from crest to crest or from trough to trough, at any given instant. Usually, these two quantities are related by the frequency formula: {eq}f = v/w {/eq}

In the above formula, f stands for frequency, v stands for wave speed, and w stands for wavelength. In the case of electromagnetic waves, v is always equal to the speed of light, at least in a vacuum. So solving for the wavelength at a given frequency, or for the frequency at a given wavelength, is a simple matter of multiplication or division. Thus, the frequencies and wavelengths of radio waves, visible light, and even X-rays are well-known quantities. This is important information to know when it comes to the construction of antennas, radio receivers, satellites, and other equipment that utilizes electromagnetic waves.

Additionally, a photon's energy can be calculated using the formula {eq}E=hf {/eq} where E stands for energy, f stands for frequency, and h stands for Planck's constant, one of the smallest constants in physics.

Electromagnetic Energy Examples

Electromagnetic energy comes in many forms. A microwave oven uses electromagnetic waves to vibrate water molecules and heats up your food. A cell phone sends electromagnetic waves to a tower, which sends them to a satellite, transmitting phone calls and text messages across the globe. In fact, all seven categories of electromagnetic radiation play important and very different roles in our everyday lives. Below are some electromagnetic radiation examples including descriptions and applications.

Radio Waves

Radio waves are low-frequency, long-wavelength electromagnetic waves. They are the least energetic and least dangerous type of electromagnetic radiation. Their wavelength is defined as any wavelength above 1 millimeter, and their frequency is defined as any frequency below 300,000,000,000 Hz. Radio waves are used for everything from car stereos to cell phones to garage door openers.

Radio towers use radio waves to send signals over immense distances.

Radio towers


Microwaves have a higher frequency and lower wavelength than radio waves, but they are still generally thought of as low-energy and are not usually thought of as dangerous to humans. Their wavelength is defined as any wavelength between 1 millimeter and 25 micrometers, and their frequency is defined as any frequency between 300,000,000,000 and 10,000,000,000,000 Hertz. Microwaves are used by microwave ovens, of course, but also by some types of radar, Bluetooth headphones and speakers, GPS, and even Wi-Fi.

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Frequently Asked Questions

What are the 7 types of electromagnetic energy?

The seven types of electromagnetic energy are listed below, from lowest-frequency and lowest-energy to highest-frequency and highest-energy: radio waves, microwaves, infrared light, visible light, ultraviolet light, X-rays, gamma rays.

What are 3 examples of electromagnetic energy?

Three examples of electromagnetic energy are visible light (like the kind emitted by the sun), microwaves (like the kind used to warm our food), and X-rays (like the kind used at a doctor's office).

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