1. Tardigrade
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  3. Physics
  4. In the given circuit the internal resistance of the 18 V cell is negligible. If R1 = 400 Ω, R3 = 100 Ω and R4 = 500 Ω and the reading of an ideal voltmeter across R4 is 5 V, then the value of R2 (in Ω) will be:

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Q. 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 $R_2$ (in $\Omega$) will be:Physics Question Image

Current Electricity

Solution:

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Across $R_4$ reading of voltmeter, $V_4 = 5 V$
Current, $i_4 = \frac{V_4}{R_4} = 0.01 \,A$
$V_3 = i_1 \,R_3 = 1\,V$
$V_3 + V_4 = 6V = V_2$
$V_1 + V_3 + V_4 = 18 V$
$\Rightarrow V_1 = 12\,V$
$ i = \frac{V_1}{R_1} = 0.03 \,A$
$i = i_1 + i_2 $
$\Rightarrow i_2 = i - i , = 0.03 - 0.01 A = 0.02 \,A$
$\therefore R_2 = \frac{V}{i_2} = \frac{6}{0.02} = 300\,\Omega$