Question

A pipe of length 85 cm is closed from one end. Find the number of possible natural oscillations of the air column in the pipe whose frequencies lie below 1250 Hz. The velocity of sound in air is 340 m/s.

• A. 6
• B. 4
• C. 12
• D. 8

Answer 1

Answer: (A)

6

In fundamental mode

$\frac{\lambda }{4}=0.85$

$\lambda =4\times 0.85$

$f=v/\lambda =\frac{340}{4\times 0.85}$

$=100Hz.$

$\therefore$ Possible frequencies = $nf$ (n is odd) = 100 Hz, 300 Hz,

500 Hz, 700 Hz, 900 Hz, 1100 Hz below 1250 Hz.