Example 1
A wave has frequency 5.0 Hz and wavelength 0.60m. Find speed and period.
v=fλ=5.0×0.60=3.0m/s. T=f1=0.20s.
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Year 11 · SACE Stage 1
Wave quantities and representations
Read wave graphs and connect speed, frequency, period and wavelength.
Method and worked examples
A wave transfers energy through a propagating disturbance. In a transverse wave, oscillation is perpendicular to travel; in a longitudinal wave it is parallel, producing compressions and rarefactions. Amplitude is the maximum displacement from equilibrium, not the full crest-to-trough height. Wavelength λ is the distance between adjacent points in the same phase, such as successive crests.
Frequency f is cycles per second in hertz and period T is seconds per cycle, with T=f1. Wave speed is v=fλ. A displacement–position graph gives wavelength; a displacement–time graph at one location gives period. Check axes and convert centimetres, milliseconds or kilohertz before substitution. Particle oscillation is not the same as net transport of the medium.
Example 1
Example 2
A displacement–position graph has crests at 0.20m and 0.80m and crest height 0.030m above equilibrium. Find wavelength and amplitude.
Adjacent-crest separation is λ=0.80−0.20=0.60m. Amplitude is 0.030m, not twice that height.
Watch out: That distance is twice the amplitude for a symmetric wave. Amplitude is measured from equilibrium to a crest or trough.