NEET AIPMT SOLVED PAPER SCREENING 2012

  • question_answer
    When a string is divided into three segments of lengths \[{{l}_{1}},{{l}_{2}}\] and \[{{l}_{3}},\] the fundamental frequencies of these three segments are\[{{v}_{1}},{{v}_{2}}\] and \[{{v}_{3}}\] respectively.   The   original fundamental frequency (v) of the string is

    A) \[\sqrt{v}=\sqrt{{{v}_{1}}}+\sqrt{{{v}_{2}}}+\sqrt{{{v}_{3}}}\]

    B) \[v={{v}_{1}}+{{v}_{2}}+{{v}_{3}}\]

    C) \[\frac{1}{v}=\frac{1}{{{v}_{1}}}+\frac{1}{{{v}_{2}}}+\frac{1}{{{v}_{3}}}\]

    D) \[\frac{1}{\sqrt{v}}=\frac{1}{\sqrt{{{v}_{1}}}}+\frac{1}{\sqrt{{{v}_{2}}}}+\frac{1}{\sqrt{{{v}_{3}}}}\]

    Correct Answer: C

    Solution :

    The fundamental frequency of string \[v=\frac{1}{2l}\sqrt{\frac{T}{m}}\] \[\therefore \]  \[{{v}_{1}}{{l}_{1}}={{v}_{2}}{{l}_{2}}={{v}_{2}}{{l}_{3}}=k\]                          ?(i) From Eq. (i) \[{{l}_{1}}=\frac{k}{{{v}_{1}}},{{l}_{2}}=\frac{k}{{{v}_{2}}},{{l}_{3}}=\frac{k}{{{v}_{3}}}\] Original length\[l=\frac{k}{v}\] Here,   \[\begin{align}   & l={{l}_{1}}+{{l}_{2}}+{{l}_{3}} \\  & \frac{k}{v}=\frac{k}{{{v}_{1}}}+\frac{k}{{{v}_{2}}}+\frac{k}{{{v}_{3}}} \\  & \frac{1}{v}=\frac{1}{{{v}_{1}}}+\frac{1}{{{v}_{2}}}+\frac{1}{{{v}_{3}}} \\ \end{align}\]    


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