What are Electromagnetic Waves: Definition & Types

What are Electromagnetic Waves: Definition & Types
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  • 0:01 Heinrich Hertz &…
  • 1:08 What Are…
  • 2:23 Types of Electromagnetic Waves
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Lesson Transcript
Instructor: Maria Howard

Maria is a teacher and a learning specialist and has master's degrees in literature and education.

Explore electromagnetic (EM) waves, their features and how they differ from other waves. Learn how EM waves are organized on a spectrum based on the amount of energy they produce, from radio waves to gamma rays.

Heinrich Hertz and Electromagnetic Waves

Who is Heinrich Hertz? If you guessed that he was the founder of the popular American car rental company with a similar name, you're not alone. But Heinrich Hertz wasn't a car rental entrepreneur. Instead, he was a German scientist who performed experiments with electricity when electricity was still a fancy new thing that scientists had a lot to learn about.

In 1888, when Hertz was 30, he made an electric spark jump from one terminal to another and noticed a second spark at the same time between two terminals a couple of yards away. Exciting stuff, I know, but this was 1888, and what Hertz noticed was a different kind of electromagnetic wave that eventually came to be known as Hertzian waves.

A few years later, in 1896, a young Italian scientist named Guglielmo Marconi built on Hertz's discovery and created the first radio transmitter, sending radio signals for a mile. (A mile!) Hertzian waves are now called radio waves and are used every day, from listening to the radio to watching TV.

What are Electromagnetic Waves?

We are surrounded by waves we can see and hear, from ocean waves to sound waves. A wave shows the transfer of energy, from the wind that starts an ocean wave to the sound that moves through the air to your ear drum. Waves that pass through a physical object or medium are called mechanical waves. Unlike mechanical waves, electromagnetic waves do not need a medium to travel or propagate. Electric and magnetic fields both produce vibrations and, together, the two types of energy create electromagnetic waves.

Waves take different shapes, but electromagnetic waves all have a snake-like shape which makes them transverse waves. Transverse waves are measured by their height, or amplitude, and by their wavelength, or the distance between the highest point of one wave, the crest, to the crest of the next wave. The lowest point of a wave is called a trough. Trough to trough can be measured, too. When analyzing an electromagnetic wave, both the amplitude and distance between waves is measured.

We measure both the amplitude, or height of a wave (a), and the distance between waves (b).
Diagram of a wavelength

One whole wave, from crest to crest, or trough to trough, is called a cycle. The number of cycles that occur per second is the wave's frequency. In honor of Heinrich Hertz, we measure frequency in hertz or Hz.

Types of Electromagnetic Waves

Electromagnetic waves are ordered on the electromagnetic spectrum by frequency. They range from radio waves with fewer cycles per second to the extraordinarily fast and harmful high frequency of gamma rays.

Radio waves have the lowest frequency of the seven bands of waves on the electromagnetic spectrum, which also means they have the least amount of energy. Radio waves have wavelengths measuring from miles to the length of a football, or around 11 inches.

It is common to talk about the frequency of radio waves, or the number of waves per second. When tuning in to a radio station, a person is listening to a specific frequency of radio waves. AM stations are numbered from 520 to 1610, with each number representing the frequency of the station at thousands of hertz per second, or kilohertz, abbreviated kHz. FM station frequencies range from 87.0 to 107.9 million hertz per second, called megahertz or MHz.

Sound is converted into EM waves and sent through radio dishes like this one. Your radio then receives these radio waves and changes them back into sound waves.
Image of a radio satellite

Next on the spectrum are microwaves, a type of radio wave that are less than 11.8 inches long. The microwaves people use to heat food have waves measuring about five inches. Microwaves aren't just for heating leftovers or cups of coffee, though. Microwaves are also used for radar, television and satellites.

Microwaves occur at higher frequencies, with billions or even trillions of cycles occurring per second. Since writing out 4,000,000 hertz is kind of clunky, it would be written as 4 gigahertz or 4 GHz. Digital radio is broadcast at a frequency of 2.5 billion hertz per second, or 2.5 GHz.

Infrared waves occur at an even higher frequency than microwaves. Infrared waves are used to power television remote controls and for thermal imaging, like when using a pair of night vision goggles. When you feel warmed by the sunlight, the energy you feel is infrared radiation from the sun. Since infrared waves have such high frequencies, their wavelengths are so tiny they are only hundredths or thousandths of an inch.

All electromagnetic waves are light, but the band of the electromagnetic spectrum that people and animals can see is called visible light. When a beam of light passes through a prism, a person can see each color of the rainbow separated into their individual wavelengths. Red, the longest of the wavelengths, measures around 700 nanometers; yellow is around 600 nanometers; and violet, the shortest, is around 400 nanometers in length.

This diagram breaks down the electromagnetic spectrum by frequency and size of wavelengths. Notice the rainbow-colored section of visible light.
Diagram of the electromagnetic spectrum

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