Question

The switch in the circuit has been closed for a long time. At t=0 is opened find v_0(t) for t>=0

Answer 1

I don't get how they get i_g=80/40, where did they get the 40 from??

Answer 2

Any ideas?

Answer 3

The easiest way too look at it (at least for now) is to notice that when the circuit is closed, the inductor is a short circuit (at DC, it has zero impedance). so the current just flows into this short, and thus we only need consider two 50 Ohms in parallel (=25Ohm) + 15 Ohm = 40 Ohms

Answer 4

I used a voltage divider to find the voltage at 50 ohms then divided to 25

Answer 5

oh sorry yeah I combined the 50 and 50 to get 25 then used voltage divider do you know how to find the i_L(0^-)?

Answer 6

I don't see how they got 2(50)/100

Answer 7

current divider rule

Answer 8

but isn't the i_L(0-) with the 50ohms and20ohms?

Answer 9

if you combine the 2ohms 3ohms and 60 and 20 together on the left you get 20 ohms then I thought you had to use the current divider with the 20 ohms and the 50 on the left

Answer 10

no, I don't think any current flows into the 20 Ohm combination on the right; it just by-passes it completely