CMC Medical CMC-Medical VELLORE Solved Paper-2008

  • question_answer
    Two stretched strings of same material are vibrating under same tension in fundamental mode. The ratio of their frequencies is 1: 2 and ratio of the length of the vibrating segments is 1 : 4. Then the ratio of the radii of the strings is

    A)  2 : 1                                      

    B)  4 : 1

    C)  3 : 2                                      

    D)  8 : 1

    E)  4 : 5

    Correct Answer: D

    Solution :

                    \[n=\frac{1}{2l}\sqrt{\frac{T}{\pi {{r}^{2}}d}}\]where\[l\]is length, T is tension, r is radius and d is density. Given,   \[\frac{{{n}_{1}}}{{{n}_{2}}}=\frac{1}{2},\]\[\frac{{{l}_{2}}}{{{l}_{1}}}=\frac{1}{4}\] \[\therefore \]  \[\frac{{{n}_{1}}}{{{n}_{2}}}=\frac{{{l}_{2}}}{{{l}_{1}}}\sqrt{\frac{r_{2}^{2}}{r_{1}^{2}}}\] \[\Rightarrow \]               \[{{\left( \frac{{{n}_{1}}{{l}_{1}}}{{{n}_{2}}{{l}_{2}}} \right)}^{2}}=\frac{r_{2}^{2}}{r_{1}^{2}}\] \[\Rightarrow \]               \[\frac{{{r}_{1}}}{{{r}_{2}}}=\frac{{{n}_{2}}{{l}_{2}}}{{{n}_{1}}{{l}_{1}}}=2\times 4=8:1\]


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