Comparing Transverse and Longitudinal Waves

All waves transfer energy without transferring matter. The two types are distinguished by the direction of particle oscillation relative to the direction of energy transfer.

Side-by-side comparison

Property	Transverse	Longitudinal
Oscillation direction	Perpendicular to energy transfer	Parallel to energy transfer
Features	Crests and troughs	Compressions and rarefactions
Can be polarised?	Yes	No
Examples	Light, water surface waves, S-waves, EM waves	Sound, P-waves, ultrasound, slinky push-pull
Representation	Sinusoidal displacement graph	Density/pressure variation graph

Polarisation

Only transverse waves can be polarised. Polarisation restricts the oscillations to one plane only.

Evidence that light is transverse: light can be polarised using a polarising filter. If two filters are crossed (at 90$^\circ$), no light passes through.

Sound cannot be polarised because the vibrations are already along one axis (parallel to propagation).

Common features

Both types:

• Transfer energy from source to detector.
• Have amplitude, wavelength, frequency and period.
• Can be reflected, refracted and diffracted.
• Obey the wave equation: $v = f\lambda$.

Common errors and how to correct them

• Saying water waves are longitudinal. Surface water waves are transverse (the surface moves up and down while the wave moves horizontally).
• Saying electromagnetic waves need a medium. EM waves can travel through a vacuum.

How to apply this in an exam

State the direction of oscillation relative to the direction of energy transfer. Give examples. If asked about polarisation, explain why only transverse waves can be polarised.