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Two tuning forks with frequencies 250 Hz and 256 Hz produce beats. If a maximum of sound intensity is observed at a certain instant, after what time interval is a minimum of intensity first observed at the same location?

1. 1/18 s
2. 1/4 s
3. 1/3 s
4. 1/12 s

Correct answer: 1/12 s

Solution

Beat frequency = 256 - 250 = 6 Hz. The beat period is 1/6 s. Maxima occur every full beat period; a minimum (destructive interference) occurs halfway between two consecutive maxima. Therefore time from maximum to next minimum = (1/6)/2 = 1/12 s.

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