Analysis of RLC Circuit v(t): Find Voltage with Ohm's Law

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SUMMARY

The analysis of the RLC circuit reveals that it is critically damped with w0 and a0 both equal to 20. The initial voltage calculation using Ohm's Law yielded an incorrect V(inf) of 36V, which should be corrected to 4V by applying Thevenin's theorem to the circuit. The current through the switch at t=0- is calculated to be 0.125A, leading to an initial voltage of V(0-) = -1V. The discussion emphasizes the importance of correctly applying circuit analysis techniques to derive accurate results.

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So I found the circuit is series, w0 and a0 equal 20 so it is critically dampened. For V(inf) I used current divider to get the equation (.1 A *120 ohm)/40 ohm = .3 A. Then I used ohms law to find v(t) = .3*120 = 36 V.

I then wrote down the circuit at t<0, t>0, and t=inf. I am stuck at this point.
 
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so t<0 will give you your initial conditions
t inf will give you your steady state value.
T>0 will give you the differential equation that you are looking for.

write out the differential equation first and solve it, either in time or frequency domains
 
Your V(inf) calculation is wrong. Substitute the two resistors to the right and the current source with a Thevenin equivalent: 40Ω in series with a 4V voltage source.
So V(inf) = 4V.

The current through the switch, I(0-) will be (4V - (-6V) ) / ( 40Ω + 40Ω ) = 0.125A (from right to left ).

So V(0-) = -6V + 0.125A*40Ω = -1V.
 

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