phy (waves)
2010-03-13 8:00 am
A loudspeaker is emitting sound waves with freq. 600Hz. The waves are reflected by a car which is moving towards it at 10m/s. Find the beats heard by a man standing near the loudspeaker.
回答 (2)
2010-03-13 8:30 pm
Take speed of sound in air = 330 m/s
Apparent frequency of sound received by the approaching car, using the Doppler shift formula.
= 600[(330+10)/330] m/s = 618.18Hz
The reflected wave also suffers a Doppler shift in frequency. The apparent frequency heard by the man
= 618.18[330/(330-10)] m/s = 637.5 Hz
Hence, beat frequency heard
= (637.5 - 600) Hz = 37.5 Hz
Apparent frequency of sound received by the approaching car, using the Doppler shift formula.
= 600[(330+10)/330] m/s = 618.18Hz
The reflected wave also suffers a Doppler shift in frequency. The apparent frequency heard by the man
= 618.18[330/(330-10)] m/s = 637.5 Hz
Hence, beat frequency heard
= (637.5 - 600) Hz = 37.5 Hz
2010-03-13 8:43 am
The car can be regarded as a moving source of freq. 600 Hz and approaching at 10 m/s
So apparent freq. heard by a stationary observer newa the loudspeaker = 600 x 330/(330 - 10) = 618.75 Hz
So beat freq. detected = 18.75 Hz
So apparent freq. heard by a stationary observer newa the loudspeaker = 600 x 330/(330 - 10) = 618.75 Hz
So beat freq. detected = 18.75 Hz
參考: Myself
收錄日期: 2021-04-29 17:34:39
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