Transverse & Longitudinal Waves (CIE AS Physics)

• In mechanical waves, particles oscillate about fixed points
• There are two types of mechanical wave:
  • transverse
  • longitudinal

• The type of wave can be determined by the direction of the oscillations in relation to the direction the wave is travelling

Transverse waves

• Transverse waves are defined as follows:

A wave in which the particles oscillate perpendicular to the direction of motion and energy transfer 

A transverse wave travelling from left to right

• Transverse waves show areas of peaks and troughs
• Examples of transverse waves include:
  • Electromagnetic waves e.g. radio, visible light, UV
  • Vibrations on a guitar string

• Transverse waves do not need particles to propagate, and so they can travel through a vacuum 
• Transverse waves can be polarised

Longitudinal waves

• Longitudinal waves are defined as follows:

A wave in which the particles oscillate parallel to the direction of motion and energy transfer 

A longitudinal wave travelling from left to right

• As a longitudinal wave propagates, areas of low and high pressure can be observed:
  • A rarefaction is an area of low pressure, with the particles being further apart from each other
  • A compression is an area of high pressure, with the particles being closer to each other

• Sound waves are an example of longitudinal waves
• Longitudinal waves need particles to propagate, and so they cannot travel through a vacuum 
• Longitudinal waves cannot be polarised

• The diagram below shows the equivalent of a wavelength on a longitudinal wave

Comparing wavelengths of longitudinal and transverse waves

Wavelength shown on a longitudinal wave

• Transverse and longitudinal waves can be represented graphically in the same way
• The main difference is the meaning of 'displacement' on the y-axis
  • Alternatively, displacement could be exchanged for velocity or acceleration

• For a transverse wave:
  • Displacement is perpendicular to the direction of propagation (energy transfer)

• For a longitudinal wave:
  • Displacement is parallel to the direction of propagation (energy transfer)

Graphical representation of a progressive wave

The wave has a period of 1.0 s, a frequency of 1.0 Hz and could be either transverse or longitudinal.