al phy(urgent

2011-01-31 8:24 am

The diagram shows a device used to demonstrated the interference of sound waves .Sound from the loudspeaker L diverts into two paths LAD and LBD.Path LBD can be varied in length. Initially, a maximum is detected at D . As B is pulled out through a distance pf 2.0 m ,two minima and two other maxima are detected.
Give two reasons why sound from the loudspeaker is still heard when a minimum is detected

回答 (1)

天同

2011-01-31 5:08 pm

✔ 最佳答案

Since a diagram is not given, I could only answer the question in a general sense.

I suppose the distances LAD and LBD are not equal. As such, if the speaker is regarded as a point source, the intensity of sound decreases with the square of distance (the inverse square law). Hence, the intensities of sound from the two paths are not the same, when they interfere, complete destructive interference would not occur.

The second reason is that there are sound scattering from the surroundings. This would give a "background" noice to the detector.

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