Doppler effect

Definition

The Doppler effect is the change in frequency or wavelength of a wave in relation to an observer moving relative to the source of the wave. It is most commonly observed with sound waves.

5 Must Know Facts For Your Next Test

1. The Doppler effect occurs when there is relative motion between a source of sound and an observer.
2. When the source of sound approaches the observer, the frequency appears higher (blue shift); when it moves away, the frequency appears lower (red shift).
3. The formula for the observed frequency $f' = f \left(\frac{v + v_o}{v - v_s}\right)$ where $f$ is the emitted frequency, $v$ is the speed of sound, $v_o$ is the velocity of the observer, and $v_s$ is the velocity of the source.
4. The Doppler effect has applications in radar and medical imaging technologies like ultrasound.
5. A sonic boom occurs when an object travels faster than the speed of sound, leading to a sudden change in pressure.

Review Questions

• What happens to the observed frequency as a sound source moves towards you?
• Write down and explain the formula used to calculate observed frequency in terms of source and observer velocities.
• How does a sonic boom relate to the Doppler effect?

Related terms

Sonic Boom:

A loud explosive noise caused by the shock wave from an object traveling faster than the speed of sound.

Red Shift:

An increase in wavelength (or decrease in frequency) observed when a wave source moves away from an observer.

Blue Shift:

A decrease in wavelength (or increase in frequency) observed when a wave source moves towards an observer.