Question

In the figure, the switch was closed for a long time before opening at t = 0. The voltage $V_x$ at $t=0^{+}$, is

• A. 25 V
• B. 50 V
• C. -50 V
• D. 0 V

Answer 1

The correct option is C -50 V

When switch was closed, circuit was in steady state,

$i_L\left(0^{-}\right)=2.5A$

$At,t=0^{+}$

$\Rightarrow V=IR$

$=2.5\times 20=50V$

$\therefore V_x=-50V$

(Polarity of $V_x$ is given reverse of V)