Definition questions are some of the quickest marks on a physics paper, and the waves topic has a lot of them. If you learn these word for word, you’ll be able to answer them in seconds.
Waves transfer energy, not matter
This is the big idea. A cork on a pond bobs up and down as ripples pass, but it doesn’t travel with them. The energy moves; the water stays where it is.
Transverse vs longitudinal
- Transverse: oscillations are perpendicular to the direction of energy transfer (water ripples, light).
- Longitudinal: oscillations are parallel to the direction of energy transfer, with compressions and rarefactions (sound).
The four definitions
- Amplitude: the maximum displacement of a point on a wave from its undisturbed position.
- Wavelength: the distance from a point on one wave to the equivalent point on the next.
- Frequency: the number of waves passing a point each second (Hz).
- Period: the time for one wave to pass a point (T = 1/f).
The classic mistake
Amplitude is measured from the middle line to the top of a crest, not from crest to trough. If a wave is 8 cm from top to bottom, its amplitude is 4 cm.
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