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RC Circuit - Post-Lab Questions

  • Thread starter chrisfnet
  • Start date
  • #1
39
0

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!
 

Answers and Replies

  • #2
393
0
For the first problem, I think your teacher wants a symbolic answer such as ".5V"

Your 4.61 time constants is right.
 
  • #3
39
0
I'm not even sure how to work either of the first two problems? It seems like I should need to know more information...
 
  • #4
39
0
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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