doppler effect
doppler effect — noun
1. The way sound or light waves appear to change in pitch or color to a person when
The way sound or light waves appear to change in pitch or color to a person when the object producing the waves moves either toward or away from that person.
An ambulance siren sounds higher as it comes closer and lower after it passes due to the Doppler effect.
illustrates pitch change with approaching then receding source
A train horn drops in pitch as the train rushes past — a familiar example of the Doppler effect.
Police radar guns use the Doppler effect to calculate a car's speed from reflected radio waves.
An ice cream truck's music changes pitch as it approaches and passes — the Doppler effect.
A racing car's roar sounds higher as it speeds toward you and deeper as it passes, showing the Doppler effect.
文法句型
the Doppler effect (noun phrase)
Doppler effect + in + {sound, light, waves}
用法筆記
Frequently used with the definite article: 'the Doppler effect.' In everyday speech it is most often used to explain why the pitch of a siren, horn, or engine changes as a vehicle passes by.
常見錯誤
2. The measurable change in the frequency of waves (such as sound, light, or radio)
The measurable change in the frequency of waves (such as sound, light, or radio) reaching an observer, caused by the movement of the wave source relative to the observer — the frequency rises as the distance shrinks and drops as the distance grows.
Astronomers detect distant planets by measuring the tiny Doppler shift in a star's light.
collocation: Doppler shift in [star's light / radio waves]
Weather forecasters use Doppler radar to track rain clouds by measuring frequency changes in reflected radio waves.
Doppler + noun: Doppler radar, Doppler ultrasound
A technician used Doppler ultrasound to measure blood flow through a damaged vein.
A teacher swung a buzzer on a rope so the class heard the Doppler effect in action.
A fire truck's siren pitch falls as it passes because the sound waves stretch out.
- Doppler shift
Often used interchangeably in physics; 'Doppler shift' emphasizes the measurable frequency change while 'Doppler effect' refers to the broader phenomenon.
文法句型
the Doppler effect (noun phrase)
Doppler shift in + {light, sound, radio waves}
用法筆記
This sense is the formal physics definition. Distinguish from sense 1 (SOUND/LIGHT CHANGE): sense 1 describes what a person observes in daily life, while sense 2 focuses on the measurable wave-frequency shift that underlies the phenomenon. Scientists often use 'Doppler shift' to refer specifically to the frequency change itself.