JEE Main & Advanced Physics Current Electricity, Charging & Discharging Of Capacitors Question Bank Heating Effect of Current

  • question_answer If a 30 V, 90 W bulb is to be worked on a 120 V line, a resistance of how many ohms should be connected in series with the bulb [MP PMT 2002; KCET 2003]

    A)            10 ohm                                   

    B)            20 ohm

    C)            30 ohm                                   

    D)            40 ohm

    Correct Answer: C

    Solution :

                       Suppose resistance R is corrected in series with bulb. Current through the bulb \[i=\frac{90}{30}=3\,A\] Hence for resistance \[V=i\,R\]Þ \[90=3\times R\Rightarrow R=30\,\Omega \]

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