Which term describes the quantity related to the energy of a wave and measured as the distance from the rest position to crest or trough?

• A. Amplitude
• B. Wavelength
• C. Speed
• D. Frequency

Answer: (A)

Amplitude describes how far a point on a wave moves from its rest position, measured as the distance from rest up to a crest (or down to a trough). This displacement is directly linked to the wave’s energy: for many waves, energy grows with the square of the amplitude, so larger amplitudes carry more energy. The distance from the rest position to the crest or trough is exactly the amplitude, which is why this term fits the description. Wavelength measures the spacing between successive crests, speed is how fast the wave travels, and frequency is how many cycles occur per unit time—none of these describe the displacement from rest that relates to energy in this way. So the correct term is amplitude.