Transverse waves

Waves are vibrations that transfer energy from place to place without matter - solid, liquid or gas - being transferred. Think of a Mexican wave in a football crowd. The wave moves around the stadium, while each spectator stays in their seat - only moving up, and then down, when it is their turn.

Some waves must travel through a substance. The substance is known as the medium, and it can be solid, liquid or gas. Sound waves and seismic waves [seismic waves: vibrations caused by earth movements ] are like this: they must travel through a medium. It is the medium that vibrates as the waves travel through it.

Other waves do not need to travel through a substance. They may be able to travel through a medium, but they do not have to. Visible light, infrared rays, microwaves, and other types of electromagnetic radiation [electromagnetic radiation: Energy travelling as waves in the form of changing electrical and magnetic fields. ], are like this. They can travel through empty space. Electrical or magnetic fields vibrate as the waves travel through them.

Transverse waves

All types of electromagnetic radiation, including visible light, are transverse waves waves. In transverse waves the vibrations are at right angles to the direction of travel, as seen in the animation below of a wave sent down a piece of string. The hand moves up and down, as does each part of the string. But the wave moves along from left to right. Water waves and s-waves - one type of seismic wave - are also transverse waves.

For your exam you need to know that lasers produce an intense narrow beam of light.