Need help finding current on RC circuit

AI Thread Summary
The discussion revolves around calculating the current in an RC circuit with three capacitors and one resistor after the capacitors have lost 80% of their initial stored energy. The user initially outlines their approach to finding the necessary charge and current using relevant equations, including energy and current formulas. They express a desire for verification of their solution, which involves logarithmic calculations and the final current value of approximately 13.9 A. There are technical difficulties with sharing images of the circuit diagram, which hindered responses from other users. Ultimately, the user resolves the image issue, allowing for a clearer discussion of their calculations.
Ruskointhehizzy
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Homework Statement


In the circuit shown in the figure each capacitor
initially has a charge of
magnitude 3.60nC on its plates. After the switch S is closed, what will be the
current in the circuit at the instant that the capacitors
have lost 80.0% of their initial stored energy?
the shown 3 capacitors are 10, 15, and 20 pF and the one resistor has 25ohms - all in series with one switch S.

Homework Equations


E = 1/2Q^2/c = QV/2
V_c(t)=Q/c * (1-e^(-t/RC))
i = Q/RC * e^(-t/RC)

I have since solved this but I would really appreciate it if I could get this checked for correctness.
Thank you.
IMG_2196.JPG


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I think I have figured out my mistake but please can I still get a check to see if my solution is correct?
first I find what Q needs to be to get .2E
to do this I say:
E0 = ½Q2/C, E = ½ ( √.2 Q )2/C = .2(½ Q2/C) = .2E0
I then use this to find -t
-t = RCln(Q/Q0) = RCln(√.2Q0/Q0) = RCln(√.2)
then finally
i = - Q/RC * e-t/RC = Q/RC * eRCln(√.2)/RC = Q/RC * eln√.2 = = -(3.6nC/(25Ω*4.62pF)) * √.2
i = = -3.6e-9C * √.2 / ( 25Ω * 4.62e-12F) = 13.9A
 
We can't see your images, which is probably why nobody has responded.
 
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phyzguy said:
We can't see your images, which is probably why nobody has responded.
Yeah I tried to post a image with a link to my google drive but it didn't let me - then when I tried to remove it wouldn't let me.
I finally resorted to posting it in the comments lmao.
Did you have a chance to check over my solution? I hope I got this correct I've been stuck on it for awhile
 
I don't see the figure anywhere. Have you tried just dragging the figure into the comment entry window?
 
FactChecker said:
I don't see the figure anywhere. Have you tried just dragging the figure into the comment entry window?
oh that worked thank you

that was just my first wrong attempt - I will change the op
 

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