What is the final charge and potential difference on each capacitor?

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Homework Help Overview

The discussion revolves around a circuit involving three capacitors (C1, C2, C3) with specified capacitances and a voltage applied across two points. The original poster seeks to determine the final charge and potential difference on each capacitor after a switch is thrown, indicating a change in the circuit configuration.

Discussion Character

  • Exploratory, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss relationships between the charges and voltages across the capacitors, with attempts to derive expressions for the charge on C1 based on the charges on C2 and C3. There is a focus on using the equation Q=CV and the implications of voltage relationships in the circuit.

Discussion Status

Some participants have confirmed the calculations for the charge on C1, indicating a level of agreement on the results obtained. However, the discussion remains open as the original poster continues to seek validation of their findings.

Contextual Notes

The discussion is constrained by the need to adhere to homework guidelines, which may limit the extent of assistance provided. There is also an implicit assumption regarding the correct application of circuit principles and equations.

ooohffff
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Homework Statement


In the circuit shown in the figure, C1 = 1.0 µF, C2 = 1.9 µF, C3 = 2.8 µF, and a voltage Vab = 30 V is applied across points a and b. After C1 is fully charged the switch is thrown to the right. What is the final charge and potential difference on each capacitor?

24-33.gif


Homework Equations



Q=CV

The Attempt at a Solution



I found everything (V1, Q2, V2, Q3, V3) except for Q1. I tried doing Q1 = CeffV1, but the answer was wrong.
 
Last edited:
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Ok so since V1=V2+V3, I did Q1/C1 = Q2/C2 + Q3/C3. Solving for Q1, I get Q1 = C1[ Q2/C2 + Q3/C3].

Q2=Q3=q

Q1=C1*q[1/C2 + 1/C3]

Plugging in the numbers, when q = 15.9μC, I get Q1 = 1.4*10-5 C. Does that look right?
 
Last edited:
ooohffff said:
Plugging in the numbers, when q = 15.9μC, I get Q1 = 1.4*10-5 C. Does that look right?
That looks right for the final charge on C1, yes.
 
gneill said:
That looks right for the final charge on C1, yes.
Thank you!
 

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