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 :

Options

A. 80 cm
B. 100 cm
C. 120 cm
D. 140 cm

Answer

C

Explanation

For closed pipe, fundamental frequency is
`f _(1) = (v)/(4L)`
For open pipe, secon overtone `= f _(3) = (3v)/(2L.)`
Here it is given that `f _(1) =f _(3)`
`therefore (v )/(4L) =(3v)/( 2L.) implies L. = 6L = 6 xx 20 = 120 cm`