An electric bulb rated as $200\, {W}$ at $100 \,{V}$ is used in a circuit having $200\, {V}$ supply. The resistance $'R'$ that must be put in series with the bulb so that the bulb delivers the same power is $.....\,\Omega$
JEE MAIN 2021, Medium
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Power, $P =\frac{ V ^{2}}{ R _{ B }}$
$R_{B}=\frac{V^{2}}{P}=\frac{100 \times 100}{200}$
$R_{B}=50 \Omega$
To produce same power, same voltage should be across the bulb
Hence, $R=R_{B}=50 \Omega$
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