Question

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 5V, then the value $R_2$ will be :

• A. $300\Omega$
• B. $230\Omega$
• C. $450\Omega$
• D. $550\Omega$

Answer 1

Answer: (A)

$300\Omega$

$V_4=5V$
$i_1=\frac{V_4}{R_4}=0.01A$
$V_3=i_1{R}_3=1V$
$V_3+V_4=6V=V_2$
$V_1+V_3+V_4=18V$
$V_1=12V$
$i=\frac{V_1}{R_1}=0.03Amp$
$i_2=0.02Amp$
$R_2=\frac{V_2}{i_2}=\frac{6}{0.02}=300\Omega$