# Need help on solving a RL circuit with switch

• Engineering

## Homework Equations

Find v(t) for t < 0 and t > 0 in the circuit.

## The Attempt at a Solution

I tried to find the i through the inductor for both t=0- and t=infinity, but I did not get the same result as the answer given in the txtbook which is 96e-4t V. According to the answer given from the txtbk, if I'm not wrong, i(t) shud be i(t)=48e-4t A, and then to find v at the 2 ohm resistor, i(t) X 2 and u get v(t).

I do not really understand why, I've been on this qn for 1 hr and stil can't understand it.
Please help and thank you.

## Answers and Replies

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berkeman
Mentor

## Homework Equations

Find v(t) for t < 0 and t > 0 in the circuit.

## The Attempt at a Solution

I tried to find the i through the inductor for both t=0- and t=infinity, but I did not get the same result as the answer given in the txtbook which is 96e-4t V. According to the answer given from the txtbk, if I'm not wrong, i(t) shud be i(t)=48e-4t A, and then to find v at the 2 ohm resistor, i(t) X 2 and u get v(t).

I do not really understand why, I've been on this qn for 1 hr and stil can't understand it.
Please help and thank you.
What's I_o?

Io is I0, the value should be calculated when t=o-

berkeman
Mentor
Io is I0, the value should be calculated when t=o-
It's a bit confusing for me, but to clarify... So the switch is opened at t=0? And right before then, there is 1*I_o flowing to the left, and 3*I_o flowing to the right? To add up to the 4*I_o that is supplied by the dependent current source in the middle?

vela
Staff Emeritus
Science Advisor
Homework Helper
Education Advisor
I think the idea is that at t=0, the 3-ohm branch is disconnected and the 8-ohm branch is connected. The controlled source is a voltage source since it has the + and - signs in it, not an arrow.

I noticed there's a little o symbol right below the arrow for current i. Is that significant?