First slide
Stationary waves
Question

An organ pipe is closed at one end has fundamental frequency of 1500 Hz. The maximum number of overtones generated by this pipe which a normal person can hear is :

Difficult
Solution

Critical hearing frequency for a person is 20,000Hz.  
If a closed pipe vibration in Nth mode then frequency of vibration n=(2N1)v4l=(2N1)n1
(where n1 = fundamental frequency of vibration)
Hence 20,000 =(2N1)×1500N=7.17
Also, in closed pipe 
Number of over tones = (No. of mode of vibration) –1
                                    = 7 – 1 = 6.

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