Uttarakhand PMT Uttarakhand PMT Solved Paper-2005

  • question_answer The two electric bulbs have 40 watt and 60w rating at 220V. Then the ratio of their resistance will be:

    A)  1 : 4             

    B)  3 : 2

    C)  4 : 3             

    D)  2 : 3

    Correct Answer: B

    Solution :

     Here: \[{{P}_{1}}=40W,{{P}_{2}}=60W\] voltage = 220V Using the relation for power \[P=\frac{{{V}^{2}}}{R}\propto \frac{1}{R}\] Or \[R\propto \frac{1}{P}\] Hence, \[\frac{{{R}_{1}}}{{{R}_{2}}}=\frac{{{P}_{2}}}{{{P}_{1}}}=\frac{60}{40}=\frac{3}{2}\] Ratio of\[{{R}_{1}}\]and\[{{R}_{2}}\]is\[3:2\]


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