Transverse & Longitudinal Waves
- In mechanical waves, particles oscillate about fixed points
- There are two types of wave: transverse and 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
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
Worked example
The diagram below represents a transverse wave at time t = 0. The direction of motion of the wave is shown. Point P is a point on the wave. State in which direction point P will move immediately after the time shown.
Step 1: Determine the possible directions that point P can travel in
- In transverse waves, the particles oscillate perpendicular to the direction of motion
- This transverse wave travels from right to left
- Oscillations will either be up or down
- Hence point P will either move up or down
Step 2: Determine the next direction of point P
- Since the wave is moving from right to left, a crest (i.e. a point of maximum displacement above the equilibrium position) will be approaching point P immediately after the time shown
- Point P will be moving upwards