Why is the RC circuit homework statement giving different results than expected?

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Homework Help Overview

The discussion revolves around an RC circuit problem where participants are analyzing the behavior of a capacitor at time t=0 and comparing calculated results to expected outcomes. The subject area is electrical circuits, specifically focusing on capacitor behavior and current calculations.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • Participants discuss the initial conditions of the circuit, particularly the role of the capacitor at t=0 and its effect on the circuit's behavior. Questions are raised about the nature of the shorting wire and its relevance to the circuit's configuration at the moment the switch is closed.

Discussion Status

The discussion is ongoing, with participants expressing confusion over the problem statement and the results they are obtaining. Some participants have calculated a current of 6 amps at t=0, while others question the correctness of the book's answer of 7 amps. There is no explicit consensus on the accuracy of the provided answers, but there is a shared sense of uncertainty regarding the problem's phrasing.

Contextual Notes

Participants note that the problem is written in a way that is unfamiliar to some, which may contribute to the discrepancies in their calculations. The assumption that the capacitor behaves as a wire at t=0 is a key point of discussion.

cupid.callin
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Homework Statement


attachment.php?attachmentid=33576&stc=1&d=1301168110.jpg


The Attempt at a Solution



As at t=0 the capacitor behaves as a wire ... so the circuit at t=0 will be like:

attachment.php?attachmentid=33577&stc=1&d=1301168676.png


q at any time for this circuit will be,

[tex]q \ = \ CE(1-e^{-t/\tau}) + Q_oe^{-t/\tau}[/tex]

differentiating it will give current,

[tex]i \ = \ \frac{Ee^{-t/\tau}}{R} \ - \ \frac{Q_oe^{-t/\tau}}{\tau}[/tex]

putting values give 6

but answer is 7
 

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Is the 1Ω shorting wire temporary? -- that is to say: is it removed before the switch is closed?
 
No ... but the question asks use for t=0 ... i.e. when capacitor behaves as a wire ... so it will short circuit the resistor ... :)
 
SOme help please ??
 
Yup, at t=0, capacitor A has zero potential across it.

At time t=0, what's the potential across capacitor B ?
 
Sorry for the delay. The problem is written in an unfamiliar way (at least for me).

I also came up with 6 amps @ t=0.
 
so that means that the answer in book is wrong?
 
I think it must be wrong.
 

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