In a given medium, the waves propagate at a certain speed.

That is, **the speed of a wave depends on the medium in which it propagates**. For example, electromagnetic waves propagate in a vacuum at a speed of 300 000 km in a single second!

Let's relate wave propagation velocity to wave elements we have already seen: frequency and period.

We already know that for a given constant propagation velocity, that is, for a wave propagating without changing medium, we have:

on what: **v **is the speed;

is the distance traveled;

It is the time.

As we know, the period being the time required to produce a complete cycle, and the wavelength the width of a crest plus a valley, we can conclude that the wave travels a wavelength in a period.

on what: is the wavelength

**T** it's the period

**f **is the frequency

Follow the situation below, where we will relate the propagation speed, frequency and period of a wave.

A periodic wave produced on a string has a frequency of 20 Hz and a wavelength of 2 m. Calculate your speed.

Therefore, the speed of this wave is 40 m / s

Since the speed of a wave in a given medium is constant, we can see that if we increase the frequency, we decrease the wavelength, and vice versa.

We then conclude that frequency and wavelength are **inversely proportional quantities**.