First slide
Standing waves
Question

The air column in a one end closed tube is oscillating in first overtone with frequency 270 Hz. Now a tube of same diameter and length is joined to the open end of the closed tube so as to make a longer pipe closed at one end. Then the fundamental frequency of air column in the composite pipe is 

Moderate
Solution

If l be the length of the closed tube, then  f=3.v4l
Length of the composite pipe is 2l.
  f'= Fundamental frequency = v4(2l)=12.f3=2706Hz=45Hz

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