JEE Main & Advanced Physics Wave Mechanics Question Bank Self Evaluation Test - Waves

  • question_answer
    The length of the wire between two ends of asonometer is 100 cm. What should be the positions of two bridges below the wire so that the three segments of the wire have their fundamental frequencies in the ratio of 1 : 3 : 5?

    A)  \[\frac{1500}{23}cm,\frac{2000}{23}cm\]

    B)  \[\frac{1500}{23}cm,\frac{500}{23}cm\]

    C) \[\frac{1500}{23}cm,\frac{300}{23}cm\]

    D) \[\frac{300}{23}cm,\frac{1500}{23}cm\]  

    Correct Answer: A

    Solution :

    [a] From formula, \[f=\frac{1}{x}\sqrt{\frac{T}{m}}\Rightarrow \frac{1}{f}\propto l\] \[\therefore \,\,{{l}_{1}}:{{l}_{2}}:{{l}_{3}}=\frac{1}{{{f}_{1}}}:\frac{1}{{{f}_{2}}}:\frac{1}{{{f}_{3}}}={{f}_{2}}{{f}_{3}}:{{f}_{1}}{{f}_{3}}:{{f}_{1}}{{f}_{2}}\] \[\left[ Given:{{f}_{1}}:{{f}_{2}}:{{f}_{3}}=1:3:5 \right]\] =15: 5: 3 Therefore the positions of two bridges below the wire are \[\frac{15\times 100}{15+5+3}cm\,\,\,and\,\,\,\frac{15\times 100+5\times 100}{15+5+3}cm\] i.e., \[\frac{1500}{23}cm,\frac{2000}{23}cm\]


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