Which statement correctly defines the amplitude of a wave?

• A. Crest is the maximum value of the wave
• B. Trough is the minimum value of the wave
• C. Amplitude is the distance from the middle to the crest
• D. Wavelength is the distance from crest to crest

Answer: (C)

Amplitude is the size of a wave’s displacement from its rest position. In a wave that oscillates around a middle position, the crest is the highest point and the trough the lowest. The amplitude is the distance from that middle line (the equilibrium position) to the crest (or, equivalently, to the trough, since both have the same magnitude). That’s why describing amplitude as the distance from the middle to the crest matches the definition. The other ideas mix in different concepts: the crest is a point of maximum displacement, not the distance itself; wavelength measures how far the pattern repeats along the direction of travel (crest to crest), not vertical displacement; and the distance from crest to trough spans twice the amplitude.