When a fire engine moves away from an observer, the pitch of the siren heard by the
observer decreases. This is because
A the wavelength of the sound wave decreases
B the speed of the fire engine increases
C the frequency of the siren decreases
D the distance travelled by each wavefront increases
why the answer is D but not C?
doppler effect
2014-03-17 12:58 am
回答 (3)
2014-03-17 1:29 am
✔ 最佳答案
When the source (i.e. the siren) is moving, the actual frequency emitted by the siren doesn't change. The moving of the source gives rise to a longer separation between successive wavefronts behind the source. Thus the wavelength appears to be longer, which leads to a lower pitch.圖片參考：https://s.yimg.com/rk/HA00458726/o/409102332.jpg
2014-03-17 2:08 am
正確答案是 D。因聲源不斷遠去，聲源所發出的震盪需走更遠的距離才可到達「觀察者」的耳朵，這便使「觀察者」每秒所接收到的震盪次數减小，從而使音調下降了。
2014-03-17 1:30 am
Simple - C is the make-up answer.
All other answers relate to Doppler effect. However, C is not related.
The frequency of the siren is controlled by the fire engine, which can be changed even the fire engine is stationary. This has nothing to do with the Doppler effect.
All other answers relate to Doppler effect. However, C is not related.
The frequency of the siren is controlled by the fire engine, which can be changed even the fire engine is stationary. This has nothing to do with the Doppler effect.
收錄日期: 2021-04-13 20:18:34
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20140316000051KK00562