## Student Features

The Electromagnetic Spectrum
What are waves?

 Ocean waves
Have you ever ridden a wave in the ocean?

Ocean waves travel on the surface of the water. You can see them and you can feel them. As you swim through the water, you can even make your own waves.

Have you ever seen a flag on a windy day?

The wind creates waves in the flag. Both the waves in the flag and the ocean waves are waves that you can see. There are other kinds of waves. We cannot see these waves, but we experience them every day. These waves are called electromagnetic waves.

Sound is also a type of wave that we cannot see. Like ocean waves, sound waves need a medium to travel through. Sound can travel through air because air is made of molecules. These molecules carry the sound waves by bumping into each other, like Dominoes knocking each other over. Sound can travel through anything made of molecules - even water! There is no sound in space because there are no molecules there to transmit the sound waves. Electromagnetic waves are unlike sound waves because they do not need molecules to travel. This means that electromagnetic waves can travel through air and solid materials - but they can also travel through empty space. This is why astronauts on spacewalks use radios to communicate. Radio waves are a type of electromagnetic wave.

What are electromagnetic waves?

Electricity can be static, like what holds a balloon to the wall or makes your hair stand on end. Magnetism can also be static like a refrigerator magnet. But when they change or move together, they make waves - electromagnetic waves.

 Electric fields and magnetic fields create an electromagnetic wave
Electromagnetic waves are formed when an electric field (which is shown in blue arrows) couples with a magnetic field (which is shown in red arrows). Magnetic and electric fields of an electromagnetic wave are perpendicular to each other and to the direction of the wave. James Clerk Maxwell and Heinrich Hertz are two scientists who studied how electromagnetic waves are formed and how fast they travel.

Electromagnetic waves have different wavelengths

When you listen to the radio, watch TV, or cook dinner in a microwave oven, you are using electromagnetic waves.

Radio waves, television waves, and microwaves are all types of electromagnetic waves. They only differ from each other in wavelength. Wavelength is the distance between one wave crest to the next.

Waves in the electromagnetic spectrum vary in size from very long radio waves the size of buildings, to very short gamma-rays smaller than the size of the nucleus of an atom.

Did you know that electromagnetic waves can not only be described by their wavelength, but also by their energy and frequency? All three of these things are related to each other mathematically. This means that it is correct to talk about the energy of an X-ray or the wavelength of a microwave or the frequency of a radio wave.

The electromagnetic spectrum includes, from longest wavelength to shortest: radio waves, microwaves, infrared, optical, ultraviolet, X-rays, and gamma-rays.

 A chart showing the electromagnetic spectrum