Amplitude as Maximum Displacement in Waves

Steps:

• Recall the standard definition: amplitude is the maximum distance a particle in a medium moves from its rest position during wave oscillation.
• Evaluate choice A: it describes the full range of motion, not the maximum from equilibrium.
• Evaluate choice B: it matches the definition precisely as the peak displacement.
• Eliminate C and D: they relate to energy or power, which depend on amplitude but are not the definition.

Why B is correct:

• By definition in wave mechanics, amplitude $A$ is the maximum displacement $x_{\max}$ from equilibrium, as in the equation $x = A \sin(\omega t + \phi)$.

Why the others are wrong:

• A: Refers to the full peak-to-peak distance, which is twice the amplitude.
• C: Energy is proportional to amplitude squared ($E \propto A^2$), but not the amplitude itself.
• D: Power relates to energy transfer rate, not directly defining amplitude.

Final answer: B