\(\def \u#1{\,\mathrm{#1}}\) \(\def \abs#1{\left|#1\right|}\) \(\def \ast{*}\) \(\def \deg{^{\circ}}\) \(\def \ten#1{\times 10^{#1}}\) \(\def \redcancel#1{{\color{red}\cancel{#1}}}\) \(\def \BLUE#1{{\color{blue} #1}}\) \(\def \RED#1{{\color{red} #1}}\) \(\def \PURPLE#1{{\color{purple} #1}}\) \(\def \th#1,#2{#1,\!#2}\) \(\def \lshift#1#2{\underset{\Leftarrow\atop{#2}}#1}}\) \(\def \rshift#1#2{\underset{\Rightarrow\atop{#2}}#1}}\) \(\def \dotspot{{\color{lightgray}{\circ}}}\)

Wavelength

This is a snapshot of a wave, at one single moment in time. The highest points of the wave are called crests, and the lowest points are called troughs. We say that two crests are in phase with each other, as are two troughs, or any two points on the wave which are identical. A crest and a trough, on the other hand, are said to be out of phase with each other.

The wavelength of a wave is the distance between two neighboring points on the wave which are in phase with each other: two crests or two troughs. We use the Greek letter symbol lambda $\lambda$ to represent the wavelength.