RAJASTHAN PMT Rajasthan - PMT Solved Paper-2010

  • question_answer
    In order to double the frequency of the fundamental note emitted by a stretched string, the length is reduced to\[\frac{\text{3}}{\text{4}}\text{th}\] of the original length and the tension is changed. The factor by which the tension is to be changed is

    A)  \[\frac{\text{3}}{8}\]                                    

    B)  \[\frac{2}{3}\]

    C)  \[\frac{8}{9}\]                  

    D)         \[\frac{9}{4}\]

    Correct Answer: D

    Solution :

    The frequency\[n=\frac{1}{2l}\sqrt{\frac{T}{m}}\]                                 \[n\propto \frac{\sqrt{T}}{l}\] The ratio of tensions                 \[\frac{{{T}_{2}}}{{{T}_{1}}}={{\left( \frac{{{n}_{1}}}{{{n}_{1}}} \right)}^{2}}{{\left( \frac{{{l}_{2}}}{{{l}_{1}}} \right)}^{2}}\]                       \[={{(2)}^{2}}\times {{\left( \frac{3}{4} \right)}^{2}}\]                       \[=\frac{9}{4}\]


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