Finding I(0)- and I(0)+ in First Order Circuit

In summary, the question is asking for the values of I(0)- and I(0)+, which represent the current right before and after time = 0 in a circuit. To find these values, the resistor equivalent (Req) on the right side must be calculated by eliminating the capacitor. Using this value, Vc (0)- can be found and then used to calculate the time constant (T) and the voltage at time (t). Finally, the current at time 0 can be found by dividing the voltage by the resistor value. However, to find the exponential form of the current after time 0, the capacitor discharge with an RC period must be taken into account.
  • #1
darwinharianto
42
0
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)+


sorry for bad English and bad picture
thx for replying in advance
 

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  • #2
Be a bit more specific: What are I(0)+ and I(0)-?

ehild
 
  • #3
ehild said:
Be a bit more specific: What are I(0)+ and I(0)-?

ehild

its the current that before and after time = 0
a moment right after for +
a moment right before for -
 
  • #4
Hello darwinharianto
See the attachment.
 

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  • #5
baby_1 said:
Hello darwinharianto
See the attachment.

oic
thanks a lot

so no need for me to the e^x
because the assignment before got e^x for the V
 
  • #6
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
baby_1 said:
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.

thanks a lot :D
now I do understand it
 

What is I(0)- and I(0)+ in First Order Circuit?

I(0)- and I(0)+ refer to the initial currents in a first-order circuit. I(0)- is the initial current in the inductor when the switch is closed, and I(0)+ is the initial current in the capacitor when the switch is opened.

Why is it important to find I(0)- and I(0)+ in First Order Circuit?

Finding I(0)- and I(0)+ is important because it helps in analyzing the transient behavior of the circuit. By knowing the initial currents, we can determine the voltages across the inductor and capacitor at the beginning of the circuit's operation.

How can I calculate I(0)- and I(0)+ in First Order Circuit?

I(0)- can be calculated by using the equation I(0)- = V(0-)/R, where V(0-) is the initial voltage across the inductor and R is the resistance in the circuit. I(0)+ can be calculated by using the equation I(0)+ = V(0+)/R, where V(0+) is the initial voltage across the capacitor.

What factors can affect the values of I(0)- and I(0)+ in First Order Circuit?

The values of I(0)- and I(0)+ can be affected by the initial conditions of the circuit, such as the initial voltage across the inductor and capacitor, the resistance in the circuit, and the time constant of the circuit.

Can I(0)- and I(0)+ be negative in First Order Circuit?

Yes, I(0)- and I(0)+ can be negative in certain cases. This happens when the initial voltage across the inductor or capacitor is greater than the voltage source in the circuit, leading to a negative initial current. However, in most cases, the initial currents are positive.

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