JEE Main & Advanced Physics Wave Mechanics Question Bank Critical Thinking

  • question_answer
    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 [IIT-JEE (Screening) 2004]

    A)            \[\frac{L}{3}\]                      

    B)            \[\frac{4L}{3}\]

    C)            \[\frac{4L}{3}\sqrt{\frac{{{\rho }_{1}}}{{{\rho }_{2}}}}\]      

    D)            \[\frac{4L}{3}\sqrt{\frac{{{\rho }_{2}}}{{{\rho }_{1}}}}\]

    Correct Answer: C

    Solution :

                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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