Waves transfer energy from one place to another without transferring matter. The particles of the medium oscillate about their rest positions but do not travel with the wave.
Evidence that waves carry energy
- Water waves can move boats up and down and erode coastlines.
- Sound waves make eardrums vibrate.
- Light waves heat surfaces and enable photosynthesis.
- Earthquake waves (seismic waves) can destroy buildings.
Evidence that matter is not transferred
- A floating cork on water bobs up and down as a wave passes but does not travel horizontally with the wave.
- Sound waves pass through air, but the air itself does not move from the speaker to the listener.
Amplitude and energy
A wave with greater amplitude carries more energy. Doubling the amplitude quadruples the energy (energy is proportional to amplitude squared, though this quantitative relationship is not required at IGCSE level).
Louder sounds have greater amplitude. Brighter light has greater amplitude (for the same frequency).
Common errors and how to correct them
Saying “waves carry matter from place to place.” Waves transfer energy, not matter. The medium (air, water, string) vibrates but stays in place.
Confusing amplitude and wavelength when discussing energy. Energy depends on amplitude (how large the vibrations are), not wavelength (the distance between peaks).
How to apply this in an exam
When asked what waves transfer, state “energy without transferring matter.” If asked for evidence, give a specific example showing energy delivery (damage, heating, vibration) and an example showing the medium stays in place (floating cork, air not moving).
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