Amplitude in Water Waves

Steps:

• Recall that amplitude measures the maximum displacement of a wave from its equilibrium position.
• In a water wave, equilibrium is the flat water level between crests (peaks) and troughs.
• The full vertical distance from trough to peak is twice the amplitude, as amplitude is from equilibrium to peak or trough.
• Thus, amplitude equals half the vertical distance between trough and peak.

Why A is correct:

• By definition, amplitude is the distance from equilibrium to the crest (or trough), which is half the trough-to-peak vertical distance.

Why the others are wrong:

• B: Describes a partial wavelength, not vertical displacement.
• C: Defines one full wavelength horizontally.
• D: Gives twice the amplitude, the full wave height.

Final answer: A