Properties

A wave is a regular vibration that carries energy.

Ripples on the surface of a pond, sound in air, ultrasound, visible light, X rays and infrared rays are all types of wave. All transverse waves have crests and troughs.

The wavelength ( ) of a wave is the length of one complete wave. The unit of wavelength is the metre.

Wave diagram

The frequency ( ) of a wave is the number of oscillations per unit time. The frequency of a wave is the same as the frequency of the source that produces the wave. The unit of frequency is the hertz.

The period (T) of a wave is the time that it takes for one complete oscillation. The unit of period is the second.

The period and frequency of a wave are linked by the following relationship,

T =

The speed (v) of a wave is the distance travelled per unit time by the wave. The unit of speed is the metre per second, m s^-1.

The speed, frequency and wavelength of a wave are linked by the following relationship,

v =

Wave phases

Points on a wave which are a whole number of wavelengths apart are said to be in phase. Points A and A¹ in the diagram above are in phase.

Points which are an odd number of half wavelengths apart are said to be out of phase. Points A and B in the diagram above are out of phase.

The energy carried by a wave depends on the amplitude of the wave. The bigger the amplitude the more energy the wave carries.

Reflection, refraction, diffraction and interference are characteristic behaviours of all types of wave.

Reflection

Reflection occurs when a wave bounces from the surface of an obstacle.

None of the properties of a wave are changed by reflection. The wavelength, frequency, period and speed are same before and after reflection. The only change is the direction in which the wave is travelling.

Wave reflection

Refraction

Refraction occurs when a wave moves from one material to another.

The speed and wavelength are changed by refraction. The frequency and period of the wave stay the same. The direction in which the wave is travelling may or may not be changed by refraction. For more detail on this, go to the section on refractive index.

Wave refraction

Diffraction

Diffraction occurs when a wave passes an edge, passes through a narrow gap or goes past an object.

None of the properties of a wave are changed by diffraction. The wavelength, frequency, period and speed are same before and after diffraction. Again, the only change is the direction in which the wave is travelling.

When a wave passes through a gap the diffraction effect is greatest when the width of the gap is about the same size as the wavelength of the wave.

Wave diffraction