A level Physics · Edexcel 9PH0 · Topic 5A

Wave properties

Key points

A progressive wave carries energy from one place to another; the particles of the medium only oscillate.
In transverse waves (light, waves on a string) oscillations are perpendicular to the direction of energy transfer; in longitudinal waves (sound) they are parallel, giving compressions and rarefactions.
Key terms: amplitude, wavelength $\lambda$ , frequency $f$ , period $T = \frac{1}{f}$ , and phase difference (in degrees or radians; one full cycle is $2\pi$ ).
Wave equation: $v = f\lambda$ .
For a wave on a string, speed depends on tension and mass per unit length: $v = \sqrt{\frac{T}{\mu}}$ .
Intensity is power per unit area, $I = \frac{P}{A}$ , and is proportional to amplitude squared.
Ultrasound pulse–echo techniques use the time taken for a reflected pulse to return: distance = $\frac{vt}{2}$ .

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