# First Order circuit

1. Jun 3, 2014

### darwinharianto

the question is to find I(0)- and I(0)+
the I is at the

what I have attempted
finding Req on the right side
I eliminate the capacitor and Req = 12*6/(12+6) = 4
so Vc (0)- = Req/(Req+12) *18 = 9/2

T = Req*c= 4*1/12 = 1/3
so V(t) = 18/4 e^(-3T)

so I (0)- = V(t)/12 = 3/8 e^(-3t)

but I don't know how to find the I(0)+

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2. Jun 3, 2014

### ehild

Be a bit more specific: What are I(0)+ and I(0)-?

ehild

3. Jun 3, 2014

### darwinharianto

its the current that before and after time = 0
a moment right after for +
a moment right before for -

4. Jun 3, 2014

### baby_1

Hello darwinharianto
See the attachment.

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5. Jun 3, 2014

### darwinharianto

oic
thanks a lot

so no need for me to the e^x
because the assignment before got e^x for the V

6. Jun 4, 2014

### baby_1

Hello darwinharianto
as you know before t(-) we assume that our circuit is in steady state so we don't have exponential form.however after t(0) capacitor tries to be discharge with RC period time so exponential form will appear.
if you want exponential form of i after t(0) follow the attachment.

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7. Jun 5, 2014

### darwinharianto

thanks a lot :D
now I do understand it