Wave Measurements

These quantities describe a wave:Displacement: the distance of a point on the wave from its equilibrium position, in a stated direction.Amplitude (A): the maximum displacement from the equilibrium position.Wavelength (λ): the distance between two adjacent crests (or two adjacent troughs).Period (T): the time taken for one complete oscillation.Frequency (f): the number of complete oscillations per second, measured in hertz (Hz).f = 1 ÷ TWave speed (v): the distance the wave travels per unit time. In one period the wave moves forward one wavelength, sov = fλOn a displacement-distance graph, the wavelength is read along the horizontal axis between repeating points. On a displacement-time graph for one point, the same repeat gives the period instead. Amplitude is measured from the centre line to a crest, not from trough to crest.Worked exampleA sound wave has a period of 2.5 ms and a wavelength of 0.85 m.f = 1 ÷ T = 1 ÷ (2.5 × 10^-3) = 400 Hzv = fλ = 400 × 0.85 = 340 m s^-1Always convert to SI units (ms to s, cm to m) before substituting.