JCECE Engineering JCECE Engineering Solved Paper-2005

  • question_answer
    An electric bulb is marked \[100\,\,W,\,\,230\,\,V\]. If the supply voltage drops to \[115\,\,V\], what is the total energy produced by the bulb in\[10\,\,\min ?\]

    A) \[30\,\,kJ\]                        

    B) \[20\,\,kJ\]

    C) \[15\,\,kJ\]                        

    D) \[10\,\,kJ\]

    Correct Answer: C

    Solution :

    From Joule's law, the total energy produced by bulb is                 \[H=\frac{{{V}^{2}}}{R}t\] Also,      \[P=\frac{{{V}^{2}}}{R}\] Given,\[P=100\,\,W,\,\,V=230\,\,volt\] \[\therefore \]  \[R=\frac{{{(230)}^{2}}}{100}=529\,\,\Omega \] Hence, heat produced\[=\frac{{{V}^{2}}}{R}\times t\] or            \[H=\frac{115\times 115}{529}\times 10\times 60\]                                 \[=15\,\,kJ\]


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