Finding Effective Capacitance in a Circuit | Voltage Across Capacitor

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    Capacitor Voltage
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Discussion Overview

The discussion revolves around finding the effective capacitance in a circuit involving multiple capacitors and the implications for calculating voltage across those capacitors. It includes elements of homework-related problem-solving and conceptual clarification regarding capacitance calculations.

Discussion Character

  • Homework-related
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions why the effective capacitance formula (1/c1 + 1/c2)^-1 requires multiplication by 2, suggesting confusion about its application.
  • Another participant proposes a method involving three equations to find the resultant voltage across the capacitors, indicating a more complex approach to the problem.
  • Some participants express difficulty in understanding the calculations presented, noting the lack of explanations for the formulas used.
  • There is a mention of a multiple-choice aspect to the problem, with one participant highlighting that several answer choices lack the correct units, suggesting a potential shortcut to the solution.

Areas of Agreement / Disagreement

Participants do not appear to reach a consensus on the effective capacitance calculation or the best approach to finding the voltage across the capacitors. Multiple competing views and methods are presented.

Contextual Notes

Some assumptions regarding the circuit configuration and the definitions of terms like effective capacitance may be missing or unclear. The discussion also indicates unresolved mathematical steps in the participants' reasoning.

Who May Find This Useful

Students working on circuit analysis, particularly those dealing with capacitors and voltage calculations, may find this discussion relevant.

delsoo
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Homework Statement


here's my question and the working in the same photo.. my question is to find to find the effective capacitance in the circuit i use (1/c1 +1/c2)^-1 , why should can't just take effective c =
(1/c1 +1/c2)^-1 but must times 2 ? since (1/c1 +1/c2)^-1 is already effective capacitance. please ignore the irrelevant part . sorry for the messy work

Homework Equations





The Attempt at a Solution

 

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Why should effective capacitance be the criterion for obtaining the resultant voltage across the capacitors?

One way:
You can write 3 equations in 3 unknowns: Qb, Q1 and Q2 where
Qb is the charge on each plate before reconnection,
Q1 is the charge on plate 1 after reconnection
Q2 is the charge on plate 2 after reconnection

Then V after reconnection is obvious.
 
Last edited:
Can you explain what you calculated? It is hard to understand that with those unexplained formulas.

By the way, as this is a multiple choice question, there is a shorter way to find the right answer: three out of four answers do not have the correct units.
 
mfb said:
Can you explain what you calculated? It is hard to understand that with those unexplained formulas.

By the way, as this is a multiple choice question, there is a shorter way to find the right answer: three out of four answers do not have the correct units.

Ho ho, good point! Lousy choices!
 

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