Question

Find the voltage $V_{ab}$ in the circuit shown in figure.

• A. +3 V
• B. - 3 V
• C. +6 V
• D. -6 V

Answer 1

The correct option is B - 3 V

Given : $I_1=2$ A

As no current flows between x and y, thus $V_{xy}=V_x-V_y=-5$ V ...........(1)

Using Kirchhoff loop law in Box 2 : $-30+(4+6)I_2=0$ $⟹I_2=3$ A

Also $V_y-V_b=4I_2=4\times 3=12$ V .........(2)

Box 1 : $V_a-V_x=-2\times 5=-10$ V ..........(3)

Adding (2) and (3) we get $V_a-(V_x-V_y)-V_b=2$

$\therefore$ $V_a-V_b+5=2$ $⟹V_a-V_b=V_{ab}=-3$ V