Hello everyone i'm confused...i was just doing RL and RC circuits without a driven source, they made sense after doing them a few 100 times. Now i'm at Driven RL circuits. My professor said:(adsbygoogle = window.adsbygoogle || []).push({});

iL(infinity) = 2mA

iL(0+) = 0.

From my understanding, i thought at infinity, the switch has been closed for a long period of time. If the switch is closed for a long period of time that means there would be no current flowing through the inductor, because you have to have changing current. So why isn't THe current of the inductor 0 at time infinity?>

At time 0+ that means the switch has just been closed, meaning your going to have a change in current. So wouldn't that be when the current through the inductor is 2mA?

Am i interpretting the unit step wrong?

2u(t) ?

this formula doesn't ask for time 0-, that means before the switch is closed, now at that point i can see how she would get iL(0-) = 0, becuase the current is totally disconnected!

Any help on explaining this would be great! :)

Also by doing it her way, she got the right answer in the back of the book.

THen she found VL, the voltage on the inductor and got the opposite, she wrote:

VL(0) = 2 mA* 3k = 6v

vL(infinity) = 0;

VL = 6e^(-t/5E-6);

x = 15mH/3k = 5E-6;

She also wrote this which i think explains why,

Current in inductor and Voltage on a capacitor can NOT change instantly

Voltage on inductor and current in a capacitaor can change indstantly

So is this why she has iL(0+) = 0? it takes time for the 2 mA to go through the inductor?

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# Driven RL circuit, why at infinity is this the current 2, and yet at 0+, its 0?

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