MCQ
A closed organ pipe of length $L$ and an open organ pipe contain gases of densities ${\rho _1}$ and ${\rho _2}$ respectively. The compressibility of gases are equal in both the pipes. Both the pipes are vibrating in their first overtone with same frequency. The length of the open organ pipe is
  • A
    $\frac{L}{3}$
  • B
    $\frac{{4L}}{3}$
  • $\frac{{4L}}{3}\sqrt {\frac{{{\rho _1}}}{{{\rho _2}}}} $
  • D
    $\frac{{4L}}{3}\sqrt {\frac{{{\rho _2}}}{{{\rho _1}}}} $

Answer

Correct option: C.
$\frac{{4L}}{3}\sqrt {\frac{{{\rho _1}}}{{{\rho _2}}}} $
c
(c) Frequency of first over tone of closed pipe $=$ Frequency of first over tone of open pipe 

$ \Rightarrow \frac{{3v}}{{4{L_1}}} = \frac{v}{{{L_2}}}$

$ \Rightarrow \frac{3}{{4{L_1}}}\sqrt {\frac{{\gamma P}}{{{\rho _1}}}} $$ = \frac{1}{{{L_2}}}\sqrt {\frac{{\gamma P}}{{{\rho _2}}}} $ 

$\left[ {\because v = \sqrt {\frac{{\gamma P}}{\rho }} } \right]$ 

$ \Rightarrow {L_2} = \frac{{4{L_1}}}{3}\sqrt {\frac{{{\rho _1}}}{{{\rho _2}}}} = \frac{{4L}}{3}\sqrt {\frac{{{\rho _1}}}{{{\rho _2}}}} $

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