Question

A constant voltage of $25\, V$ is applied to a series $L-R$ circuit at $t=0$, by closing a switch. What is the potential difference across the resistor and the inductor at time $t=0$ ?

• A. 0 V , 25 V
• B. 12.5 V , 1.25 V
• C. 10 V , 15 V
• D. 25 V , 0 V

Answer 1

Answer: (A)

At, $t=0$, switch closes

Current $i=i_{0}\left[1-e^{-t R / L}\right]$
So, at $t=0, i=0$
So, potential across inductor $=25\, V$
and across resistor $=0\, V$