A level revision

Introduction to waves

Waves carry energy from one point to another. They can be described as either transverse or longitudinal

Transverse waves are caused by vibrations acting at right angles to the direction of movement. Light and all other electromagnetic waves are transverse.

Sound is an example of a longitudinal wave. The vibrations move in the same direction as the movement as a series of compressions and rarefactions (decompressions).

The features of a wave

Waves have a number of features which you need to know about:

• Displacement is given the letter x and is the distance between a point on a wave and the line of zero disturbance (i.e. the line at which there is no vibration)
• Amplitude is given the letter a, it is the maximum displacement - the highest point of the wave.
• Wave length is given the symbol (lambda) and is the distance between two similar points on a wave.

All these values are measured in metres. In graphic form:

Other features of a wave include:

• Frequency is given the letter f and is the number of cycle made in a second. It is measured in Hertz (Hz)
• Time period is the given the letter T and is the time taken for one complete cycle of the wave - the time from one peak to another

Time period and frequency are related by the equation:

Waves also have a speed, given by the letter v

The wave equation

The wave equation relates a wave's speed, wave length and frequency by the formula: