RL Circuit with current source

1. May 8, 2014

dwn

1. The problem statement, all variables and given/known data

Image

2. Relevant equations

Current divider

3. The attempt at a solution

The only thing I see is that I solve for R1 and R2 for t < 0. Other than that I'm confused and not even sure I'm right about solving t<0.

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2. May 9, 2014

Staff: Mentor

Up until t=0, what is the equation for current through R2?

How does the circuit change at t=0?

3. May 9, 2014

dwn

Current Divider : 2 ( R1 + R2)/R1

The source is gone, stuck in the closed loop (essentially), and the inductor becomes the current source (the energy within the inductor decays exponentially).

4. May 9, 2014

Staff: Mentor

That fraction is > 1.0 ?

So what is the general form of the equation describing this decay?

5. May 9, 2014

dwn

Oh no I'm sorry, it should be 2* ((Rtotal/R1))
Rtotal = (R1*R2)/(R1 + R2)

Ie-Rt/L (R equivalent)

6. May 9, 2014

Staff: Mentor

Which resistor carries that current?

7. May 9, 2014

dwn

R2, if I'm not mistaken.

8. May 9, 2014

Staff: Mentor

Guessing is not advisable. Don't you have some way to work it out?

9. May 9, 2014

dwn

Of course, the reason I put that was bc the forum requires min 4 characters...

We choose the "unwanted" resistor to divide from the total because it has something to do with impedance (never covered this topic in class). I know the larger the resistance the less current flowing through it.

Last edited: May 9, 2014
10. May 9, 2014

dwn

The bread crumbs are not helping.