Which parameter describes the distance between successive waves along the direction of propagation?

• A. Propagation speed
• B. Amplitude
• C. Period
• D. Wavelength

Answer: (D)

Wavelength describes the distance between successive waves along the direction of travel. It’s the spatial period of the wave—the length over which the pattern repeats. If you scan along the direction the wave is moving, the distance from one crest to the next crest (or from one trough to the next trough) is the wavelength, usually measured in meters. This spatial relationship ties into how fast the wave moves: v = f λ, where v is the propagation speed, f is the frequency, and λ is the wavelength. The other properties have different meanings: propagation speed is how fast the wavefront travels; amplitude is how tall the wave is (its intensity or strength); period is the time between successive crests passing a fixed point, not the spatial distance between crests.