In this topic you will learn about waves that cannot be seen.

The way waves carry energy from place to place depends on the kind of wave motion. Sound waves are made by vibrations of particles that travel in the same direction as the sound energy. Water waves are different than sound waves. As energy moves in one direction, matter moves in a different direction.

Some waves can travel through a vacuum. These waves can travel without matter or through matter. Such waves are caused by electromagnetism. Electromagnetism is the production of magnetism by electricity and the production of electricity by magnets.

Light is electromagnetic energy. Electromagnetic waves vibrate back and forth across the direction in which light travels. The wavelength is the distance from one wave crest to the next wave crest. Light is many wavelengths. All wavelengths of light travel at the same speed. Light slows down when it travels through matter.

Scientists have another idea of how light travels. Perhaps light travels as tiny bundles of energy. Scientists call the bundles photons. We know that there are wavelengths of light that we do not see. All the wavelengths of visible and invisible light in order from short wavelengths (gamma rays) to long wavelengths (radio waves) make up the electromagnetic spectrum.

Radio waves are the longest waves of the electromagnetic spectrum. Broadcast stations use them to carry signals as a code. Radar uses radio waves that reflect off many objects. The waves can help weather forecasters detect rain and thick fog. Microwaves are shortwave radio waves absorbed by water in food. Water absorbs energy from the microwaves. As water molecules move faster, the food gets hotter.

Ultraviolet (UV) light is made up of waves just shorter than visible violet light on the spectrum. UV light causes chemical changes. It can produce vitamin D in your body. UV light from the Sun causes sunburn. X rays and gamma rays have great penetrating power. X rays can provide a picture when they pass through an arm, leg, or your jaw.

A laser is a device that produces a thin stream of light of just a few close wavelengths. Laser light does not spread out or become weaker. Powerful laser beams can melt even the hardest metals.