AP Physics 1 Question 128: Answer and Explanation
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8. A string of fixed tension and linear mass density is attached to a vibrating speaker. It is observed that a speaker frequency of 60 Hz does not produce standing waves in the string. Which explanation for this phenomenon is correct?
- A. The string length is not a multiple of half the wavelength of the wave.
- B. The wave speed on the string is fixed.
- C. 60 Hz is in the lowest range of audible sound.
- D. The wavelength of the wave produced by the speaker is equal to the speed of waves on the string divided by 60 Hz.
Correct Answer: A
A-Standing waves on a string only exist when the wave pattern produces a node at each end. A wavelength is measured node-to-node-to-node; so half a wavelength is node-to-node. If the string length isn't a multiple of this node-to-node distance, then some fraction of a wave pattern would be left on one end rather than a node. That can't happen on a fixed string, so no standing waves exist.