QJEEM14Phec41: JEE Main 2014 Physics - Class 11 JEEM14Phec41 Solution: A pipe of length 85 c m is closed from one end. Find the number …

Length of pipe $$=85$$ $$cm$$ $$=0.85m$$

Pipe is closed from one end so it behaves as a closed organ pipe

Frequency of oscillations of air column in closed organ pipe is given by,

$$f=\frac{\left(2n-1\right)\upsilon }{4L}$$

$$f=\frac{\left(2n-1\right)\upsilon }{4L}\le 1250$$

$$\Rightarrow \frac{\left(2n-1\right)\times 340}{0.85\times 4}\le 1250$$

$$\Rightarrow 2n-1\le 12.5\approx 6$$

Possible value of n = 1, 2, 3, 4, 5, 6

So, number of possible natural frequencies lie below 1250 Hz is 6.