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A closed organ pipe has a fundamental frequency of 1.5 kHz. The number of overtones that can be distinctly heard by a person with this organ pipe will be (Assume that the highest frequency a person can hear is 20,000 Hz)

1. 4
2. 7
3. 6
4. 5

Correct answer: 6

Solution

A closed pipe supports odd harmonics: 1.5, 4.5, 7.5, 10.5, 13.5, 16.5, 19.5 kHz are all <= 20 kHz (7 frequencies). The fundamental is 1.5 kHz, so the number of overtones distinctly heard = 7 - 1 = 6.

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