Waves

Waves are everywhere, giving us everything that allows the modern world to work, from sound, to microwaves, to wireless internet.

Wave properties

There are many properties that waves have: firstly, the direction in which they go in, which is the difference between transverse and longitudinal waves.

Longitudinal waves look like this:

Transverse waves look like this:

There is also another property that waves have: whether they travel through solids, liquids and gases (known as mechanical waves) or through electrical and magnetic fields.

The other properties that waves have are:

• rest position – where the wave is when particles aren’t vibrating
• displacement
• peak (highest point above rest position)
• trough (lowest point below rest position)
• amplitude (maximum displacement of a point from rest position)
• wavelength (distance covered by one wave)
• time period (time taken for one wave to pass)
• frequency – number of waves that pass a point in a second

These properties are shown on a transverse wave below:

Reflection and refraction

Waves can be reflected between a boundary of two different materials. The law of reflection says that a wave will be reflected to the same place as it approached the material at. So, if a wave touched a material at 85 (the angle of incidence) degrees, it would be reflected at 85 (the angle of reflection.)

Below is a diagram with all the properties you need to know about:

There are 2 types of reflection: specular reflection and diffuse reflection.

Specular reflection happens from a smooth, flat surface such as a mirror.

Diffuse reflection happens from a rough surface. Waves reflected from this kind of object are scattered in all directions.

Refraction is an optical illusion where waves seem to come from a different place than where they actually came from.

Example questions

To work out the wave speed, we need to use the following formula:

wave speed (m/s) = frequency (Hz) x wavelength (λ)

Now let’s try that formula with a sample question:

What is the speed of a wave with a frequency of 50Hz and a wavelength of 2 metres?

To work out the wave speed, we multiply the frequency by the wavelength. So, in this case, we need to multiply 50 by 2, which gives us 100.

So the speed of this wave is 100 m/s.

Work out the frequency of a wave going at 3 m/s with a wave length of 7m.

So, in order to do this, we need to rearrange the formula (if you want to know how to do this, scroll down to the heading with “Rearranging formulas”. For this question, the rearranged formula is frequency = wave speed (divided by) wave length.

To work out the frequency of this wave, we need to divide 3 by 7, which gives us 0.42Hz.

Or you can download the worksheet here with the answers here.