Question

The fundamental frequency of a closed organ pipe of length `20 cm` is equal to the second overtone of an organ pipe open at both the ends. The length of organ pipe open at both the ends is
A. `80 cm`
B. `100 cm`
C. `120 cm`
D. `140 cm`

Answer 1

Correct Answer - C
Fundamental frequency of closed organ pipe
`f_c=(v)/(4l_c)`
Fundamental frequency of open organ pipe
`f_0=(v)/(2l_0)`
Second overtone frequency of open organ pipe
`=(3v)/(2l_0)`
From question,
`(v)/(4l_c)=(3v)/(2l_0)`
`l_0=6l_c=6xx20=120cm`