RAJASTHAN ­ PET Rajasthan PET Solved Paper-2012

  • question_answer
    If two wires made of tinned copper having identical cross-section but different lengths \[{{l}_{1}}\]and\[{{l}_{2}}\]respectively are used as fuse wires, then the fuses will melt at same value of current in both of them

    A)  True

    B)  False

    C)  Insufficient data

    D)  None of the above

    Correct Answer: A

    Solution :

     We know that, \[R=\rho \frac{l}{a}\] \[R=\rho \frac{l}{\pi {{r}^{2}}}\] \[\therefore \]Heat produced per second \[={{I}^{2}}\times \rho \frac{l}{\pi {{r}^{2}}}\] Rate of loss of heat per unit surface area, \[H=\frac{{{I}^{2}}\rho \frac{l}{\pi {{r}^{2}}}}{2\pi rl}=\frac{{{I}^{2}}\rho }{2{{\pi }^{2}}{{r}^{3}}}\] As the heat is independent of\[l\]so both the wires will fuse at the same value of current because they have same\[\rho \]and r.


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