NEET Physics Wave Mechanics NEET PYQ-Wave Mechanics

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\[=340\,m{{s}^{-1}}\])     [NEET 2014]

A) 4

B) 5

C) 7

D)      6

Correct Answer: D

Solution :

For pipe closed at one end

\[{{f}_{n}}=n\left( \frac{v}{4l} \right)\] here n is an odd number.

\[=n\left[ \frac{340}{4\times 85\times {{10}^{-2}}} \right]\]

\[=n[100]\]

Here, n is an odd number, so for the given condition n can go up to \[n=11\] because for \[n=13\] condition will not be valid.

\[N=1,\text{ }3,\text{ }5,\text{ }7,\text{ }9,\text{ }11\]

So, number of possible natural oscillations could be 6.