# RL Circuit

## Homework Statement

The switch in the circuit has been closed for a long time before opening at t = 0
a. Find i(t) across R3 for t>0.
b. Find i(t) across R2 for t>0.

I have attached the circuit.

## The Attempt at a Solution

The only thing I know for this problem is that when a switch has been in a certain state for a long time an inductor acts essentially like a wire (no resistance) and when the state changes the inductor has infinite resistance.

#### Attachments

• HW7-1.jpg
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To solve this you need to know the formula for di/dt for RL circuits. Isn't this in your textbook or covered by lecture?

I apologize....I thought that I included the relevant equations.....but this is what I know:

What I don't understand is what the change in time is...I really don't know how to go about solving this problem...and I have no examples from lecture...all I have from lecture is basically the 2 equations I have included. Any help would be greatly appreciated...Thanks.

So I've done some work and this is what I've came up with...I'm not sure if this is even remotely close:

I applied KVL's around each loop

Am I even on the right track with this?