Doppler Effect: What is it, sound, light and formulas

The doppler effect is a physics phenomenon related to the perceived frequency variation of a wave in motion relative to an observer.

This effect was studied by the Austrian physicist Christian Doppler (1803-1853) and the discovery was named after him. hence, effect doppler.

The Doppler effect can be observed in any and all electromagnetic waves, such as light, or mechanical waves, such as sound.

Illustrative image of the Doppler effect at rest (left) and in motion (right)

In this way, the effect is perceived from the movement. As the source of sound or light approaches, the perceived frequency increases and as you move away from the observer, the frequency decreases.

Doppler Effect Formulas

It is important to realize that the wave propagation frequency does not vary. The formula refers to the wave frequency captured by the observer.

Classic formula (sound)

Thus, the classic formula for the doppler effect used for its relationship with sound is:

• When source and observer approach: + in the numerator and - in the denominator.
• When source and observer move away: - in the numerator and + in the denominator.

In the case of sound, which is easier to be observed, it can be noticed that the sound tends to become lower as the source moves away from the observer.

The perceived frequency varies according to the movement in relation to the observers

Relativistic formula (light)

In the case of light, as they get closer, their frequency tends to the ultraviolet (higher frequency) and as they move away, they tend to infrared (lower). This variation is observed by astronomers in relation to the movement of light in space.

Astronomer Edwin Hubble observed that neighboring galaxies when observed show a "shift to the red", which demonstrates that its perceived light is at a lower frequency (trending to red) than the issued.

In this way, he deduced that the other galaxies are moving away from ours, implying that the universe is expanding. Hubble's Law was based on the doppler effect.

Unlike sound, light propagates independently of a medium, its speed will always be. Its formula is based only on the relative velocity between the source and the observer.

Interested? See too:

• Sound waves
• Waves in Physics