In physics, some things are like particles, other things are like rays. Things that are like rays are for example radiation,heat and sound. Light can behave either like a particle, or as a ray.

For those things that behave like rays, there is some oscillation (going up and down, like a wave in the sea). One characteristic is the length of the wave. This is the distance the wave has travelled before its movement is in the same spot again. You start when it is at logical zero, going up, and you wait till it is again at that spot, then you wait till it is in the same position again, and measure the distance.

The wavelength is commonly designated by the Greek letter lambda (λ).

In a sine wave, the wavelength is the distance between the midpoints of the wave:

Physics

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