# RC circuit natural response, two capacitors

Discussion in 'Homework Help' started by stinz, Oct 19, 2008.

1. ### stinz Thread Starter New Member

Sep 25, 2008
1
0
Hello, I could use some help to analyze this circuit.
The problems are as follows:

1. Find the current i0(t) for t>0
2. Find the voltage v0(t) for t>=0
3. Find the energy,w(t), stored in the circuit when t->infinity

I've managed the first problem by finding the equivalent capacitance when t>0 which I found to be 100nF.
Problem 2, I'm not sure where to start. Problem 3 cannot be solved without solving problem 2.

Help would be much appreciated

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2. ### Ratch New Member

Mar 20, 2007
1,068
3
stinz,

You first have to determine the initial voltage on the capacitors at t=0. Then by the classical differential equation method or the Laplace method solve what the current is when the two capacitors discharge through the resistor. It will be some exponential function.

Ratch

3. ### hitmen Active Member

Sep 21, 2008
159
0
I am not sure if I got the correct answer cos I only deal with one capacitor question.

for t<0 , V8k = 200V
V150nf = 200V
V300nf = 180V

for t>0 io(t) = 10mA
Vo(t) = 180V

Total energy = E8K + E2k + E150nF + E300nf
= 25(8) + 10(2) + 0.5(150*10^-9)(200)(200) + 0.5(300power-9)(180)(180)

= 220W.

My answers could be wrong. Take care.

But I am confident that answers for t<0 is correct. Take care and get back to us cos I also wish to know the answr

Mar 20, 2007
1,068
3
hitmen,