Stored energy among a capacitor arrangement

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    Capacitor Energy
AI Thread Summary
The discussion focuses on solving a problem related to the stored energy in a capacitor arrangement with specific capacitances and a potential difference. The user has successfully calculated values for charge and potential difference for capacitors 2 and 3 but is struggling with the stored energy for capacitor 1. They suspect a rounding issue with the voltage value for capacitor 1, which may affect their calculations. Suggestions include maintaining more significant figures in calculations and considering the order of electron flow through the capacitors. The user is encouraged to provide a clearer image of the circuit for better assistance.
Destroxia
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BEFORE YOU READ THE REST: Problem (f) is the only one I need help with. Thank you! I have already confirmed all my other values as correct in my online program!

1. Homework Statement


In the figure a potential difference V = 150 V is applied across a capacitor arrangement with capacitances C1 = 14.8 µF, C2 = 4.27 µF, and C3 = 4.22 µF. What are (a) charge q3, (b) potential difference V3, and (c) stored energy U3 for capacitor 3, (d) q1, (e) V1, and (f) U1 for capacitor 1, and (g) q2, (h) V2, and (i) U2 for capacitor 2?

http://edugen.wileyplus.com/edugen/courses/crs7165/art/qb/qu/ch0/EAT_13632548498390_6123878003864797.gif

C1 = 14.8 µF
C2 = 4.27 µF
C3 = 4.22 µF
V1 = 33.5 V
V2 = 116.4 V
V3 = 150 V
q1 = 496.5 µC
q2 = 496.5 µC
q3 = 633 µC
U1 = (NO IDEA) I keep getting anywhere from .00830 to .00831 and .00832
U2 = .0289 J
U3 = .0475 J

Homework Equations



q = V*C

1/CT = 1/C1 + 1/C2 + ... + 1/Cn (for a series)

CT = C1 + C2 + ... + Cn (for parallel)

U = (1/2) q^2/C = (1/2)QV = (1/2)CV^2

The Attempt at a Solution



So basically, I have solved for everything except problem (f), which I don't understand because my values for U2 and U3 were correct.

I have tried every variation of the stored energy equation, and have tried all forms of significant figures (my program does uncertainty +/- 1 from the 3rd significant figure).

I have also wondered if maybe the fact that the electrons travel through C2 first, before reaching C1, that it may have some effect upon the stored energy of C1, and I have tried adding, subtracting, you name it, the two values.

I'm kind of stuck at this point.
 
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Your graphic isn't showing, it's probably behind a login:password. You can take a screenshot, clip it to just the circuit, and attach that.
 
The value of 33.5 V for capacitor 1 has a rounding issue that has a relevant impact. If you want to use this to get the energy, keep more digits. Apart from that, it looks fine, it is just a rounding issue.

(I don't see the image either, I reverse-engineered the setup based on the calculated values :D)
 
NascentOxygen said:
Your graphic isn't showing, it's probably behind a login:password. You can take a screenshot, clip it to just the circuit, and attach that.

mfb said:
The value of 33.5 V for capacitor 1 has a rounding issue that has a relevant impact. If you want to use this to get the energy, keep more digits. Apart from that, it looks fine, it is just a rounding issue.

Sorry about that guys, I was going to change the image but it said my thread was deleted so I couldn't find it until I got mfb's notification for some reason.

Anyway, I wonder why the program didn't place my value of 33.5 V as incorrect because it is based upon significant figures?

Here is the image anyway:

9qk1sz.jpg
 
RyanTAsher said:
(my program does uncertainty +/- 1 from the 3rd significant figure)
Probably due to this reason.
 
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