Wavelength, speed and frequency

EstablishedPhysics

\htmlClass{sjt-lambda}{\lambda} = \frac{\htmlClass{sjt-c}{c}}{\htmlClass{sjt-f}{f}}

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\lambda

WavelengthRosetta entry →

Meaning

Distance from one crest to the next, in metres.

Its job in this equation

The output: how stretched-out the wave is.

Picture it

The spacing between ripples on a pond.

Read it, progressively

1. Gist

At a fixed speed, faster waves (higher frequency) are shorter.

What it does not establish

It assumes a single, steady frequency. Real signals are mixtures of many frequencies (Fourier analysis), and in dispersive media $c$ is not one number. It says nothing about amplitude, which is how strong the wave is.

Play with it

λ = c / f · wavelength, speed, frequency

Frequency f1 HzWave speed c4 m/s

f1 Hz

c4 m/s

λ = c/f4 m

T = 1/f1 s

For a wave moving at speed c, one crest passes every period T = 1/f, so crests sit λ = c/f apart. Raise f at fixed speed and the wavelength shrinks. The same relation covers rope waves, sound and light; only the value of c differs (in a medium, c means that medium’s wave speed). Rope animation runs in real time. Light colours are approximate.

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