Question

In the given circuit, the current $I_1$ is

• A. 0.4 A
• B. -0.4 A
• C. 0.8 A
• D. -0.8 A

Answer 1

Answer: (B)

The circuit can be simplified as follows:

Applying $KCL$ at junction $A$
$I_3=I_1+I_2$ ....... (i)
Applying Kirchhoff's voltage law for the loop $ABCDA$
$-30I_1-40I_3+40=0$
$\Rightarrow -30I_1-40\left(I_1+I_2\right)+40=0$
$\Rightarrow 7I_1+4I_2=4$ .....(ii)
Applying Kirchhoff's voltage law for the loop $ADEFA$,
$-40I_2-40I_3+80+40=0$
$\Rightarrow -40I_2-40\left(I_1+I_2\right)=-120$
$\Rightarrow I_1+2I_2=3$ ......(iii)
On solving equations (ii) and (iii), $I_1=-0.44A$