How is a wavelength measured?

A wavelength is defined as the distance between successive points of a wave that are in phase. The correct method to measure it can vary based on the specific reference points chosen, but the fundamental concept remains the same.

When measuring wavelength, the distance can effectively be captured by determining the length between specific features of the wave. While measuring from crest to crest or trough to trough also provides valid measurements of wavelength, the description that encompasses the full wave cycle more completely involves measuring from the peak of one wave to the valley of the subsequent wave. This broader view highlights the cycle of oscillation and allows for a clear understanding of the wave's behavior.

The option selected provides a reference that includes both extremes (the peak and valley) and encompasses the entire wave cycle being measured, making it a comprehensive representation of the wavelength within the wave's periodic motion.