Amplitude Defines Wave Displacement from Equilibrium

Steps:

• Recall that amplitude is a measure of wave intensity, related to how far particles move from their rest position.
• Examine each option: A describes energy, not displacement; B confuses full wave height with amplitude; C matches the standard definition; D refers to frequency.
• Eliminate A, B, and D as they mismatch core wave properties.
• Confirm C aligns with physics: amplitude is half the distance from crest to trough.

Why C is correct:

• By definition, amplitude is the maximum distance a wave's particle displaces from its equilibrium position, as in the wave equation $y = A \sin(\omega t + \phi)$, where $A$ is amplitude.

Why the others are wrong:

• A: Energy relates to amplitude squared ($E \propto A^2$), but amplitude itself is displacement, not energy.
• B: This describes twice the amplitude (full crest-to-trough height), not amplitude alone.
• D: This defines frequency, measured in hertz, unrelated to displacement.

Final answer: C