J & K CET Engineering J and K - CET Engineering Solved Paper-2003

  • question_answer
    Two wires made up of the same material are of equal lengths but their radii are in the ratio of\[1:2\]. On stretching each of these two strings by the same tension, the ratio between the fundamental frequencies is                 

    A)  \[1:4\]          

    B)  4 : 1               

    C)  \[2:1\]          

    D)  \[1:2\]               

    Correct Answer: C

    Solution :

    The fundamental frequency of a wire is given by \[n=\frac{1}{2l}\sqrt{\frac{T}{m}}\] where I is length of wire, T the tension and m the mass per unit length. \[m=\frac{mass\text{ }of\text{ }wire}{length\,of\,wire}\] \[=\frac{\pi {{r}^{2}}L\times density}{L}=\pi {{r}^{2}}d\] \[n=\frac{1}{2l}\sqrt{\frac{T}{\pi {{r}^{2}}d}}\] \[\Rightarrow \] \[n=\frac{1}{2rl}\sqrt{\frac{T}{\pi d}}\] \[\therefore \] \[\frac{{{n}_{1}}}{{{n}_{2}}}=\frac{{{r}_{2}}}{{{r}_{1}}}=\frac{2}{1}\]


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