Stored energy among a capacitor arrangement

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    Capacitor Energy
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Homework Help Overview

The discussion revolves around a capacitor arrangement with given capacitances and a potential difference. The original poster seeks assistance specifically with calculating the stored energy for capacitor 1, while they have confirmed the correctness of other values related to charge and potential differences for the capacitors.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • The original poster attempts to use the stored energy equation but encounters difficulties, questioning the impact of the order in which the capacitors are charged. Some participants suggest that rounding issues with the voltage for capacitor 1 may affect the energy calculation.

Discussion Status

Participants are exploring the implications of significant figures and rounding on the calculations. There is no explicit consensus yet, but some guidance regarding the importance of precision in calculations has been offered.

Contextual Notes

There is mention of a graphic that is not visible to some participants, which may limit the understanding of the circuit setup. The original poster notes that their program allows for uncertainty in the calculations, which may be relevant to the discussion.

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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