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.

http://suprfile.com/src/1/bx0wa2/lastscan.jpg [Broken]

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

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