RC Circuit - Post-Lab Questions

AI Thread Summary
The discussion focuses on understanding the voltage behavior of capacitors in RC circuits during charging and discharging. For charging from zero voltage, there is confusion about whether to set VMaximum to zero and the necessity of knowing VBattery. The second question addresses how long it takes for a capacitor to discharge to less than 1% of its initial voltage, with calculations suggesting approximately 4.61 time constants are needed. Participants express uncertainty about the initial problems, indicating a need for additional information to solve them effectively. Overall, the conversation highlights the complexities of analyzing RC circuits and the importance of understanding the underlying equations.
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Homework Statement



What is the voltage across a capacitor after a time of two constants when charging from zero voltage. When discharging from a fully charged condition?

Homework Equations



VCapacitor = VBattery(1 - e-t/2T)

VCapacitor = VMaximum * e-t/2T

The Attempt at a Solution



I'm confused at how to start. I can do the algebra...

Charging from zero voltage - so would I set VMaximum to 0? Wouldn't I need to know VBattery? That wouldn't make sense to me. If I can get an idea of how to approach this problem, I should be able to solve it no problem. Thanks!

----------------------------------------------------------------------------------------

Homework Statement



With V = Vo*e-t/RC, it mathematically takes an infinite time for a capacitor in an RC circuit to discharge. Practically, how many time constants does it take for a capacitor to discharge to less than 1% of its initial voltage?

Homework Equations



V = Vo*e-t/RC

The Attempt at a Solution



0.01*Vo = Vo*e-t/RC
0.01 = e-t/RC
100 = et/RC
ln(100) = t/RC
2*ln(10)*RC = t

So, I'm saying that it takes approximately 4.61 time constants.

Would this be correct? Thanks!
 
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For the first problem, I think your teacher wants a symbolic answer such as ".5V"

Your 4.61 time constants is right.
 
I'm not even sure how to work either of the first two problems? It seems like I should need to know more information...
 
Anyone? I've been trying to work the first two still, and I just can't get past the fact that I think that I need more information.
 

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