Incandescent bulbs are designed by keeping in mind that the resistance of their filament increases with the increase in temperature. If at room temperature, $100 \mathrm{~W}, 60 \mathrm{~W}$ and $40 \mathrm{~W}$ bulbs have filament resistances $\mathrm{R}_{100}, \mathrm{R}_{60}$ and $\mathrm{R}_{40}$, respectively, the relation between these resistances is

  • [IIT 2010]
  • A

    $\frac{1}{R_{100}}=\frac{1}{R_{40}}+\frac{1}{R_{60}}$

  • B

    $\mathrm{R}_{100}=\mathrm{R}_{40}+\mathrm{R}_{60}$

  • C

    $\mathrm{R}_{100}>\mathrm{R}_{60}>\mathrm{R}_{40}$

  • D

    $\frac{1}{R_{100}}>\frac{1}{R_{60}}>\frac{1}{R_{40}}$

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  • [AIEEE 2012]

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