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BCECE Engineering BCECE Engineering Solved Paper-2004

  • question_answer
    The resistance of a bulb filament is 100\[\Omega \] at a temperature of \[100{}^\circ C\]. If its temperature                 coefficient of resistance be \[0.005/{}^\circ C\], its resistance will become 200\[\Omega \] at a temperature of:

    A) \[300{}^\circ C\]                              

    B)        \[400{}^\circ C\]

    C)        \[500{}^\circ C\]                              

    D)        \[200{}^\circ C\]

    Correct Answer: B

    Solution :

    Let resistance of bulb filament is \[{{R}_{0}}\]at\[0{{\,}^{o}}C\]  then from expression \[R={{R}_{0}}[1+\alpha \,\Delta \theta ]\] we have, \[100={{R}_{0}}[1+0.005\times 100]\] and    \[200={{R}_{0}}[1+0.005\times x]\] where\[x\]is temperature in\[{{\,}^{o}}C\]at which resistance becomes\[200\,\Omega .\] Dividing the above two equations, we have \[\frac{200}{100}=\frac{1+0.005x}{1+0.005\times 100}\]                 \[\Rightarrow \]               \[x=400{{\,}^{o}}C\]


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