Question

The number of possible natural oscillations of air column in a pipe closed at one end of length $85cm$ whose frequencies lies below $1250Hz$ are:
(velocity of sound $=340m{s}^{-1}$)

• A. $4$
• B. $5$
• C. $7$
• D. $6$

Answer 1

The correct option is D $6$

Fundamental frequency of a closed organ pipe is $f_1=\frac{V}{4l}=\frac{340}{4\times 0.85}=100Hz$
The natural frequencies of the organ pipe will be $f=100Hz,300Hz,500Hz,700Hz,900Hz,1100Hz$ which are below 1250 Hz