Waves transport energy from one place to another. They are temporary displacement in either matter or fields. The temporary displacements are called (vibrations). Waves may be either transverse or longitudinal based on how the particles (or field potentials) move in relation to direction the wave is travelling.

• In a transverse wave the oscillations are perpendicular to the direction of energy transfer.
• In a longitudinal wave the oscillations are parallel to the direction of energy transfer.

Longitudinal waves show areas of in which the particles are closer together than normal, and in which they are spread out more than normal.

Electromagnetic waves are , sound waves are and waves may be either.

The maximum displacement is known as the of a wave and is measured from the , this is where the matter (or field) would be if there wasn't a disturbance.

,

We can also measure the , this is simply the distance between two identical parts of the wave. For ease we normally measure peak to peak or trough to trough.

There are two related time measurements we can make. The is the amount of time to complete one cycle (wave) and is the number of cycles (waves) in a bit of time. One cycle per second is one hertz.

If a wave has a wavelength, λ and a frequency, f, then the wave speed, c, can be calculated by:

c = λ f

where:	c	=	Wave speed in ,
	λ	=	Wavelength in ,
	f	=	Frequency in ,

Complete the table below (to 1 s.f.):
Hint: All types of EM wave travel at the same speed in a vacuum

Wave	Frequency ()	Wavelength ()	Speed ()
Yellow light	0.51 x 10 15	590 x 10 -9	x 10 8
X - rays	_____	0.1 x 10 -9	x 10 8
Microwave	6 x 10 9	_____	x 10 8
Radio waves from space	_____	0.8	x 10 8