How light travels

In a nutshell

Light travels as a transverse wave which can be modelled using a rope. Light waves are able to travel through a vacuum at a speed of $300\,000\,000\,m/s.$

Light waves

Light travels as a transverse wave. A transverse wave is a wave that undulates at right angles to the direction of travel. Light waves have an amplitude, a frequency and a wavelength that depend on its colour.

Science; Waves; KS3 Year 7; How light travels

1.	Undulations
2.	Trough
3.	Wavelength
4.	Crest
5.	Amplitude
6.	Direction of travel

Modelling light waves

You can easily model light waves by using a rope or a string. If one person holds one end, and another moves the other up and down, you will be able to see transverse waves travelling down the rope.

Note: Notice how if you focus on one part of the rope, it doesn't move along the rope at all, only up and down. This is how a transverse wave behaves - the undulations are up and down whilst the direction the wave travels in is across.

Light travelling through a medium

Sound waves cannot travel through a vacuum, but light waves are able to. This is because light does not need a medium to travel through. The speed of any light wave in a vacuum is $300\,000\,000\,m/s$ . This is the maximum speed of light, it cannot go any faster than this.

Light can travel through transparent and translucent materials but not things like stone walls. This is because light waves are absorbed by the wall and cannot pass through. This is the reason that you are not able to see through walls.

Comparing light waves and sound waves

Light waves and sound waves behave differently.

A sound wave is a longitudinal wave.

Properties	Light waves	Sound waves
Type of wave	Transverse	Longitudinal
Speed in air	$300\,000\,000\,m/s$	$343\,m/s$
Can it travel through a vacuum?	Yes	No
What types of matter can it travel through?	Solids, liquids and gases if they are translucent or transparent.	Solids, liquids and gases
How can we detect it?	Eyes, Cameras	Ears, Microphones

Example

The speed of light in air is much faster than the speed of sound in air. This means you are more likely to see an event before you hear it. For example, if you've ever watched a thunderstorm, you may have noticed you can see the lightning before you can hear it.