Every mechanical wave moves its medium in one of two ways: side to side across the direction of travel, or back and forth along it. The distinction decides whether a wave can be polarised.
In a transverse wave the oscillations are perpendicular to the direction of energy travel (light, waves on strings). In a longitudinal wave the oscillations are parallel to it, producing compressions and rarefactions (sound). Only transverse waves can be polarised.
Switch between transverse and longitudinal and watch how the particles move relative to the energy travel. The same displacement-distance graph can represent both.
The same ideas, two geometries.
| Type | Oscillation | Examples |
|---|---|---|
| transverse | oscillation perpendicular to travel | light, string waves, water ripples |
| longitudinal | oscillation parallel to travel | sound, compression waves |
Four quick checks tied to this lesson. Each correct answer earns XP and lights this skill on your star map.
In a transverse wave, the oscillations are:
In a longitudinal wave, the particles oscillate:
Which of these is a longitudinal wave?
Regions of a longitudinal wave where the particles are pushed closest together are called:
The two types behave differently when passed through a polariser.
Do not confuse the graph shape with the motion. A displacement-distance graph of a longitudinal wave often looks like a transverse sine curve, but the real particle motion is back and forth along the travel direction. The distance between adjacent compressions is one whole wavelength, just as between adjacent crests.
Unlocks once the checks above are done. Worth more XP, written to AS Paper 1 and 2 standard.
Which type of wave can be polarised?
A sound wave and a light wave have the same frequency. Which statement is correct?
The distance between two adjacent compressions in a longitudinal wave is equal to:
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