Which term is used for the distance between successive wave crests or troughs in a progressive wave?

• A. Wave Train
• B. Wind Duration
• C. Astronomical Tide
• D. Wavelength

Answer: (D)

Wavelength is the distance between successive wave crests (or troughs) in a progressive wave. This spacing defines the wave’s spatial pattern on the surface and is measured in meters. The speed of a wave is tied to its wavelength and frequency through v = f × λ, so longer wavelengths relate to different speeds for a given frequency. The other options describe different ideas: a wave train is a group of waves traveling together, wind duration is how long the wind blows to generate waves, and astronomical tide is the regular tidal rise and fall caused by celestial gravity, not the spacing of wave crests.