Doppler effect

Definition

The Doppler effect is the change in frequency or wavelength of a wave in relation to an observer who is moving relative to the wave source. It is commonly observed with sound waves, where the pitch changes as the source and observer move towards or away from each other.

5 Must Know Facts For Your Next Test

1. The Doppler effect explains why a siren sounds higher-pitched as it approaches you and lower-pitched as it moves away.
2. It can be expressed mathematically by the formula $f' = f \frac{v + v_o}{v + v_s}$, where $f'$ is the observed frequency, $f$ 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.
3. For light waves, this phenomenon causes redshift when objects move away and blueshift when they approach.
4. The Doppler effect has applications in radar technology, medical imaging (ultrasound), and astronomy.
5. The perceived change in frequency depends on both the speed of sound in the medium and the relative velocities of both source and observer.

Review Questions

• What happens to the pitch of a sound as its source moves towards you?
• How does the Doppler effect apply to light waves?
• What factors influence the observed frequency change according to Doppler's formula?

Related terms

Redshift:

An increase in wavelength (and corresponding decrease in frequency) of light from an object moving away from an observer.

Blueshift: A decrease in wavelength (and corresponding increase in frequency) of light from an object moving towards an observer.

Ultrasound: A type of imaging that uses high-frequency sound waves to visualize internal structures within a body.