In the given circuit the internal resistance of the $18\,V$ cell is negligible. If $R_1 = 400 \,\Omega ,\,R_3 = 100\,\Omega $ and $R_4 = 500\,\Omega $ and the reading of an ideal voltmeter across $R_4$ is $5\,V,$ then the value of $R_2$ will be ........... $\Omega$
JEE MAIN 2019, Medium
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$\frac{12}{400}=\frac{6}{600}+\frac{6}{R_{2}}$
$\Rightarrow \quad \frac{1}{200}=\frac{1}{600}+\frac{1}{R_{2}}$
$\Rightarrow \quad \mathrm{R}_{2}=300\, \Omega$
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