Waves

True or false? Electromagnetic waves need air particles as a medium to travel through.

Waves

Stella was hoping to go surfing today, but there’s not a wave to be seen! How disappointing! Hey, Stella, look what happened when you threw that stone into the ocean! When it hit the surface of the water, it created a disturbance. This disturbance then travelled outwards in the form of circular ripples on the water.

How? Water is made of tiny particles. When water is still, it has low energy, and the particles don’t move much. But a moving stone carries energy, and when it hits the surface, this energy is passed onto the water particles. The particles are set in motion and the surface of the water is disturbed.

Water particles closest to where the stone landed start moving up and down. As they do so, they pull along the particles beside them. These, in turn, pull the particles that are next to them. As the particles oscillate up and down, they create regular peaks and troughs. You see it as a ripple on the surface of the water that travels outwards.

A ripple is a disturbance that transfers energy from one place to another in a regular and organised way. It is a wave. Ocean waves work in the same way. Individual particles in the wave move up and down, pulling particles that are nearby along with them, causing those to move up and down too. Even though it looks like the wave is moving towards the shore, the individual particles are moving mostly up and down around their original position.

And how far the particles move, as well as how fast the wave moves across the surface of the water, tells us how much energy a wave carries. A tall wave that moves fast towards the shore carries more energy than a small ripple that moves slowly on the surface of the water. Do you hear that seagull, Stella? The sound you hear is a wave too! When a seagull makes a sound, it causes a disturbance that pushes air particles.

These particles bump into the air particles next to them, causing those particles to move as well. Air particles move back and forth, creating regions where particles are packed tightly, and regions where they are further apart. The disturbance – this time a sound – transfers energy from one place to another in an organised manner — a wave! In this case, the particles move along in the same direction as the wave itself. Waves on the water and sound waves both need something to travel through — a medium.

A medium can be anything made up of particles — matter, so any solid, liquid or gas. Waves like these, that require a medium to travel through, are mechanical waves. But energy can be transferred as waves even in a vacuum, where there are no particles. Take energy from the sun, for example. It travels as vibrations of electric and magnetic fields as light.

This makes light an example of an electromagnetic wave. Other examples of electromagnetic waves include microwaves and radio waves, which allow the transmission of information such as radio signals and internet data. Check this out, Stella! There’s wind in the forecast for tonight, so tomorrow looks like a great day for surfing. In the meantime, why not take advantage of the electromagnetic waves around you?

Try sunbathing and surfing the net, instead!