Transverse & Longitudinal Waves
Transverse & Longitudinal Waves
- In a transverse wave the vibration is at right angles to the direction the wave travels.
- In a longitudinal wave the vibration is along the direction the wave travels.
The two types, side by side
Definition
1 markWhat is meant by transverse wave?
Model answer: A wave in which the particles vibrate at right angles to the direction of wave travel or energy transfer.
Definition
1 markWhat is meant by longitudinal wave?
Model answer: A wave in which the particles vibrate parallel to the direction of wave travel or energy transfer.
- Take a long spring (a slinky) on a bench. Move the end from side to side and the wave runs along the spring while each coil moves across: that is transverse.
- Push and pull the end in and out instead, and you send squashed and stretched regions along the spring: that is longitudinal.
- The squashed regions are compressions; the stretched regions are rarefactions. In sound these are just high and low air pressure.
longitudinal
push and pulltransverse
move side to side| Transverse (vibrate across) | Longitudinal (vibrate along) |
|---|---|
| light and all EM waves | sound |
| waves on a string or rope | compression (pressure) waves |
| a rope wave | waves along a pushed slinky |
Check the direction of vibration: across the travel direction = transverse; along it = longitudinal. Sound is the longitudinal one to remember.
Read the plotted quantity before the curve
- A longitudinal wave can be represented by a graph, but the graph is not the physical shape of the wave.
- On a particle-displacement graph, a compression is where neighbouring particles have moved towards one another. It is not automatically a crest.
- On a pressure or density graph, a maximum represents a compression. Always read the vertical axis before interpreting the curve.
Common mistake
Sound is longitudinal. If a question shows a sound wave drawn as a sine, that sine is only a convenient picture. The air still vibrates back and forth along the wave, not across it.
Your turn9702-style
State the difference between a transverse wave and a longitudinal wave. [2]
Show worked answer
In a transverse wave the particles vibrate at right angles to the direction of energy transfer. In a longitudinal wave they vibrate parallel to it.