AFMC AFMC Solved Paper-2010

  • question_answer
    There are two electric bulbs of 40 W and 100 W. Which one will be brighter when first connected in series and then in parallel?

    A) 40 W in series and 100 W in parallel

    B) 100 W in series and 40 W in parallel

    C) 40 W both in series and parallel will be uniform

    D) 100 W both in series and parallel will be uniform

    Correct Answer: B

    Solution :

    As \[\frac{{{R}_{1}}}{{{R}_{2}}}=\frac{{{P}_{2}}}{{{P}_{1}}}=\frac{100}{40}=\frac{5}{2}.\]Resistance of 40 W bulb is \[\frac{5}{2}\]times than 100 W. In series, \[P={{i}^{2}}R\]and in parallel, \[P=\frac{{{V}^{2}}}{R}.\]So, 40 W is series and 100 W in parallel will glow brighter.


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