What are the parts of a wave?

• A. Crest, trough, wavelength, and amplitude
• B. Crest
• C. Trough
• D. Wavelength

Answer: (A)

A wave has features that describe its shape and size: the crest is the highest point, the trough is the lowest point, the wavelength is the distance between successive crests (or troughs), and the amplitude is how tall the wave is from its resting position to a crest (or to a trough). The full set of terms—crest, trough, wavelength, and amplitude—captures both the form and the size of a wave. The other options each mention only one part: crest alone, trough alone, or wavelength alone, which don’t fully describe what a wave looks like or how long it is.