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JCECE Engineering JCECE Engineering Solved Paper-2009

  • question_answer
    A \[30\,\,V,\,\,90\,\,W\] lamp is to be operated on a \[120\,\,V\]\[DC\] line. For proper glow, a resistor, of\[...\Omega \] should be connected in series with the lamp.

    A) \[40\]                                   

    B) \[10\]

    C) \[20\]                                   

    D) \[30\]

    Correct Answer: D

    Solution :

    Resistance of the lamp                 \[{{R}_{0}}=\frac{{{V}^{2}}}{p}=\frac{{{(30)}^{2}}}{90}=10\Omega \] Current in the lamp                   \[i=\frac{30}{10}=3A\] When lamp is operated on a\[120\,\,V\], then resistance                 \[R'=\frac{V'}{i}=\frac{120}{3}=40\Omega \] Thus, for proper glow, the resistance required to the put in series will be                 \[R=R'-{{R}_{0}}=40-10=30\Omega \]


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