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CET Karnataka Medical CET - Karnataka Medical Solved Paper-2006

  • 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 \[i=\frac{30}{10}=3\Omega \] 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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