RC Circuit Discharge Conceptual Question

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Discussion Overview

The discussion centers on the conceptual understanding of the discharge behavior of an RC circuit when a switch is closed. Participants are exploring the implications of closing the switch on the voltage and current flow in the circuit, particularly focusing on nodes B and C and the capacitor's behavior.

Discussion Character

  • Conceptual clarification, Debate/contested

Main Points Raised

  • One participant notes that when the switch is closed, the two 6kΩ resistors become irrelevant, questioning why a current would flow from the capacitor from node B to node C.
  • Another participant points out that while node B is at zero volts before and after the switch is closed, the voltage across the capacitor may change, implying that this could affect current flow.
  • A third participant asserts that the solution manual is incorrect, suggesting that the voltage across the capacitor remains constant at 3 volts.
  • One participant agrees with the assertion that the voltage across the capacitor should always be 3 volts, reinforcing the previous claim.

Areas of Agreement / Disagreement

Participants express disagreement regarding the behavior of the capacitor's voltage when the switch is closed, with some asserting it remains constant while others suggest it may change.

Contextual Notes

The discussion does not resolve the assumptions regarding the behavior of the capacitor or the implications of closing the switch on the circuit's voltage and current flow.

DaleSwanson
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http://i.imgur.com/ZCcaZpq.png
ZCcaZpq.png


I have the solution manual, so this is more just a question of why, rather than what.

I understand that with the switch open:
vA = 3v
vB = vC = 0v
i0 = 0.25 mA

When the switch closes it creates a short that makes the two 6kΩ resistors irrelevant. What I don't understand is why anything should change then. The solution manual tells me that a current would flow from the capacitor from B to C, but why? It seems like nodes B and C should be at 0v both before and after the switch is closed.
 
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Yes, node B is at zero both before and after the switch is closed, but after the switch is closed, what is the voltage across the capacitor? Is it any different than before the switch is closed?
 
You are right--book is wrong.
 
As far as I can tell the voltage across the capacitor should always be 3v.
 

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