Question

For a certain organ pipe three successive resonance frequencies are observed at 425 Hz, 595 Hz and 765 Hz respectively. If the speed of sound in air is 340 m/s, then the length of the pipe is ___ m.

Answer 1

The frequencies are in the ratio of 5 : 7 : 9

Hence, it is a closed pipe.

$425Hz=5\left(\frac{v}{4l}\right)$

or

$l=\frac{5v}{4\times 425}$

$=\frac{5\times 340}{4\times 425}=1.0m$