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Current Electricity question

2012 · Q144
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Current Electricity question

2012 · Q144

NEETPhysicsCurrent ElectricityMCQ+4 / −1
If voltage across a bulb rated 220 volt-100 watt drops by 2.5% of its rated value, the percentage of the rated value by which the power would decrease is
  1. A
    20%
  2. B
    2.5%
  3. C
    5%
  4. D
    10%
View written solutionFree

Correct answer: C

Resistance of bulb is constant

P=V2R⇒Δpp=2ΔVV+ΔRRP = {{{V^2}} \over R} \Rightarrow {{\Delta p} \over p} = {{2\Delta V} \over V} + {{\Delta R} \over R}P=RV2​⇒pΔp​=V2ΔV​+RΔR​

∴Δpp=2×2.5+0=5%\therefore {{\Delta p} \over p} = 2 \times 2.5 + 0 = 5\%∴pΔp​=2×2.5+0=5%

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