The diagram is a snapshot of a wave on a rope. Four distances are labelled P, Q, R and S. Which distance is equal to the amplitude of the wave?
Question 1 Report
The diagram is a snapshot of a wave on a rope. Four distances are labelled P, Q, R and S. 
Which distance is equal to the amplitude of the wave?
Answer Details
The amplitude of a wave is the maximum displacement from the equilibrium (rest) position. On a transverse wave diagram, this is the vertical distance from the central horizontal line to either the crest or the trough.
Looking at the labelled distances in the diagram:
- P is the horizontal distance from one crest to the next crest, which measures the wavelength.
- Q is a horizontal distance covering half a wavelength.
- S is the total vertical distance from the crest to the trough, which equals twice the amplitude.
- R is the vertical distance from the rest position (the horizontal line) to the crest. This matches the definition of amplitude exactly.
A common mistake is to confuse R with S. The full crest-to-trough height (S) is double the amplitude. Amplitude is always measured from the rest position to one extreme, giving R as the correct answer.
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