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  4. A 220 V , 50 Hz AC source is connected to a 25 V, 5 W lamp and an additional resistance R in series (as shown in figure) to run the lamp at its peak brightness, then the value of R (in ohm) will be .

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Q. A $220\, V , 50 \,Hz$ AC source is connected to a $25\, V, 5\, W$ lamp and an additional resistance $R$ in series (as shown in figure) to run the lamp at its peak brightness, then the value of $R$ (in ohm) will be _______.Physics Question Image

JEE MainJEE Main 2022Current Electricity

Solution:

$P = Vi$
$5=25 i$
$i=\frac{1}{5}$
$V_{R}=i R$
$(220-25)=\frac{1}{5} R$
$R=195 \times 5=975\, \Omega$