Question

The current (i) at time $t=0$ and $t=\infty$ respectively for the given circuit is

• A. $\frac{18E}{55},\frac{5E}{18}$
• B. $\frac{10E}{33},\frac{5E}{18}$
• C. $\frac{5E}{18},\frac{18E}{55}$
• D. $\frac{5E}{18},\frac{10E}{33}$

Answer 1

Answer: (D)

At $t=0$, current through inductor is zero,
hence $R_{eq}=(5+1)\Vert (5+4)=\frac{18}{5}$
$i_1=\frac{E}{18/5}=\frac{5E}{18}$
At $t=\infty ,$ inductor becomes a simple wire and now the circuit will be as shown in figure
hence $R_{eq}=(5\Vert 5)+(4\Vert 1)=\frac{33}{10};(\Vert \Rightarrow$ parallel $)$
$i_2=\frac{E}{33/10}=\frac{10E}{33}$