# Light Waves: Definition, Types & Uses

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Lesson Transcript
Instructor: David Wood

David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

This lesson will define electromagnetic waves, explaining the distinction between them and 'light waves.' We will also discuss the various kinds of waves in the electromagnetic spectrum and their uses. A short quiz will follow.

## Definition of Light Waves

You are surrounded by electromagnetic waves. They're everywhere! From the light you can see, to the infrared your body is producing, to the ultraviolet coming through your window from the sun. You could not escape the waves if you tried. But then again, why would you want to?

The term light waves can be used differently by different people. Physicists tend to casually use 'light waves' to mean exactly the same thing as electromagnetic waves, but most non-physicists do not. So, what is the difference?

Electromagnetic waves (or electromagnetic radiation) are waves made of oscillating magnetic and electric fields, and include radio waves, microwaves, infrared, visible light, ultraviolet, x-rays and gamma rays. Like all waves, they carry energy, and that energy can be very high-intensity (like the electromagnetic waves we receive from the sun). When looking at the visible light spectrum, the blue end of the electromagnetic spectrum is high frequency, high energy and short wavelength. The red end of the electromagnetic spectrum is low frequency, low energy and long wavelength.

Light is just one part of the electromagnetic spectrum, the part that our eyes can see. So when most people talk about light waves, this is what they mean. However, in physics, 'light waves' often refer to any and all waves in the electromagnetic spectrum, and this is what we will discuss in this lesson.

## The Different Types of Light Waves

Radio waves are at the red end of the electromagnetic spectrum. The red end is also the lowest energy, the lowest frequency and the longest wavelength.

Radio waves are mostly used in communications, to send signals from one place to another. Radio stations, unsurprisingly, use radio waves, as do cell phones, televisions, and wireless networking. Due to the long wavelength of radio waves, they can be bounced off the Earth's ionosphere, allowing radio stations to transmit their broadcasts over long distances, without being in line-of-sight of all their listeners.

Microwaves are the next closest to the red end of the spectrum. You can probably guess that microwaves are used in our kitchen microwaves to cook your food. They are of a high enough energy that they can increase the motion of the molecules in your food without ionizing the atoms (allowing electrons to escape). This is important, because it means that the food will only be heated - its chemical composition will remain the same.

Infrared has a wavelength just a little longer than what our eyes can detect. The human body has a temperature that produces radiation in this part of the spectrum, and so infrared detectors can be used as night-vision cameras. Infrared is also used by remote controls to send signals to televisions and other AV equipment.

Visible light is the part of the electromagnetic spectrum that our eyes can detect and so is the part we are most familiar with in our everyday lives. It is considered to be in the 'middle' of the electromagnetic spectrum, though this is fairly arbitrary.

Ultraviolet (often shortened to UV) is heading into the blue side of the electromagnetic spectrum, which is the high energy and shorter wavelength side. Ultraviolet is just a little too short in wavelength for our eyes to detect. UV waves are high enough energy that they are capable of ionizing atoms, breaking molecular bonds and even damaging DNA molecules. For this reason, it is UV that causes sunburn and, therefore, skin cancer. Most of the sun's harmful UV waves are absorbed by the atmosphere (especially Nitrogen) and the ozone layer, but enough gets through that we have to be careful by wearing sunscreen and using UV eye protection.

X-Rays are very high energy and, like UV, they can ionize atoms in the body and cause damage. However, at the right wavelengths and in the right quantities, they can be safely bounced off body tissues to create x-ray images of the inside of the human body. X-rays are also created by neutron stars, black holes and nebulae, and x-ray telescopes are, therefore, useful in astrophysics research.

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