Question

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

• A. 12
• B. 8
• C. 6
• D. 4

Answer 1

Answer: (C)

The fundamental frequency
$n=\frac{v}{4l}=\frac{340\times 100}{4\times 85}=100Hz$
and as only odd harmonics are heard in a pipe closed at one end, the possible frequencies are $100,300,500,700,900,1100,1300$, etc.
$\therefore$ The frequencies below $1250$ are
$100,300,500,700,900$ and $1100$ .
Thus the number of possible natural oscillations is $6$ .