IGCSE Physics / Properties of waves
Amplitude, wavelength, frequency, period and wavefronts
Edexcel International GCSE Physics (4PH1), chapter 10: Properties of waves, specification point 3.3. Free lesson.
Read the revision notes · IGCSE Physics past papers
Wave properties describe the size and repeating pattern of a wave. You need to define them accurately and identify wavelength or period from the correct type of graph.
What the parts of a wave show
The rest position is where the material would be when there is no wave. A crest is the highest point and a trough is the lowest point. Displacement is how far a point has moved from its starting position. Amplitude is measured from the rest position to a crest or trough, not from crest to trough. Wavelength is measured between matching points on neighbouring waves, such as crest to crest.
What the five wave terms mean
Learn these definitions and units. Amplitude and wavelength describe distances, while frequency and period describe how waves pass a point over time. Amplitude: the maximum displacement of a point from its rest position. Unit: metre (m). Wavelength: the distance from one point on a wave to the same point on the next wave. Unit: metre (m). Frequency: the number of waves passing a point each second. Unit: hertz (Hz), where 1 Hz is one wave per second. Period: the time for one complete wave to pass a point. Unit: second (s). Wavefront: a line joining points on a wave that are…
How to read a displacement-distance graph
A displacement-distance graph is a snapshot of the whole wave at one instant. Distance is on the horizontal axis and displacement is on the vertical axis. Because the horizontal axis shows distance, the length of one repeat is the wavelength. Read the amplitude vertically from the middle, or rest position, to a crest. Read the wavelength horizontally between matching points, such as one crest and the next.
How to read a displacement-time graph
A displacement-time graph follows one point on the wave as time passes. Time is on the horizontal axis and displacement is on the vertical axis. The time taken for one repeat is the period. Read the period between matching points in successive cycles, such as one crest and the next. The horizontal repeat is time, so it gives the period, not the wavelength.
How to avoid the amplitude mistake
Crest to trough is the full height of the wave, so it is twice the amplitude. Always measure amplitude from the rest position.