Progressive Waves


All waves are caused by oscillations and all transfer energy without transferring matter. This means that a water wave can transfer energy to you sitting on the shore without the water particles far out to sea moving to the beach.

Here is a diagram of a wave; it is one type of wave called a transverse wave. A wave consists of something (usually particles) oscillating from an equilibrium point. The wave can be described as progressive; this means it is moving outwards from the source.

We will now look at some basic measurements and characteristics or waves.


Amplitude, A                                                                                                Amplitude is measured in metres, m

The amplitude of a wave is the maximum displacement of the particles from the equilibrium position.

Wavelength, λ                                                                                            Wavelength is measured in metres, m

The wavelength of a wave is the length of one whole cycle. It can be measured between two adjacent peaks, troughs or any point on a wave and the same point one wave later.

Time Period, T                                                                                            Time Period is measured in seconds, s

This is simply the time is takes for one complete wave to happen. Like wavelength it can be measured as the time it takes between two adjacent peaks, troughs or to get back to the same point on the wave.

Frequency, f                                                                                                    Frequency is measured in Hertz, Hz

Frequency is a measure of how often something happens, in this case how many complete waves occur in every second. It is linked to time period of the wave by the following equations:   and

Wave Speed, c                                                                      

Wave Speed is measured in metres per second, m s-1

The speed of a wave can be calculated using the following equations:


Here c represents the speed of the wave, f the frequency and λ the wavelength.

Phase Difference   


Phase Difference is measured in radians, rad

If we look at two particles a wavelength apart (such as C and G) we would see that they are oscillating in time with each other. We say that they are completely in phase. Two points half a wavelength apart (such as I and K) we would see that they are always moving in opposite directions. We say that they are completely out of phase.

The phase difference between two points depends on what fraction of a wavelength lies between them