F.6 physics (sound waves) 急!

2009-02-10 12:58 am

1. If an observer receives 'sound waves' form two sources whose frequencies differ slightly, he may detect periodic rises and falls in the intensity known as 'beats'. Explain, with the aid of diagrams or graphs, what is meant by the terms 'sound waves' and 'beats'.

2. Light from two monochromatic sources whose wavelengths differ slightly is shone onto a screen. Discuss whether 'optical beats' ( i.e. a phenomenon identical to beats in sound) can be observed.

[ From New Way Physics for Advanced Level Wave Motion (Book2) ]

回答 (1)

天同

2009-02-15 9:48 am

✔ 最佳答案

1. [Sound wave] is a longitudinal vibration of air molecules with frequency between 20 Hz to 20,000 Hz (the audible range).
[Beats] are fluctuating volume of sound caused by superposition of two sound waves of slightly different frequencies.
The relevant diagrams can be found on the following web-page:
http://www.school-for-champions.com/science/sound_beat.htm
2. No.
Ordinary light is incoherent, i.e. there is a change of phase with time, any optical beat that produced will not be stable and this would average out any variation of light intensity.

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