How do you measure wavelength?

• A. Measure two adjacent points on a wave
• B. Use a ruler to measure the wave physically
• C. Count cycles per second
• D. Use color interference patterns

Answer: (A)

Wavelength is the distance of one complete cycle of a wave. The direct way to measure it is to measure the distance between two adjacent points that are in the same phase, such as two successive crests (or troughs). That separation is the wavelength.

Other approaches aren’t as direct: using a ruler to measure the wave can be impractical if the wave is moving or not clearly showing a full cycle; counting cycles per second gives frequency, not length, unless you also know the wave’s speed; using color interference patterns can reveal wavelength for light but relies on interference physics rather than a straightforward spatial measure along the wave.