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Question:

The number of possible natural oscillations of air column in a pipe closed at one end of length 85 cm whose frequencies lie below 1250 Hz are: (velocity of sound = 340 m/s)

4

7

6

5

Solution:

Fundamental frequency of a closed organ pipe is
f1=V/4l=340/4×0.85=100Hz
The natural frequencies of the organ pipe will be
f=100Hz,300Hz,500Hz,700Hz,900Hz,1100Hz
which are below 1250 Hz