What is the steady state voltage across the capacitor in this open circuit?

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Homework Help Overview

The problem involves determining the steady state voltage across a capacitor in an open circuit configuration. The context includes a multiple choice question with various potential voltage values related to a direct current (DC) source.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants discuss the behavior of the capacitor in steady state, with some suggesting that the capacitor behaves as an open circuit, while others question the implications of the circuit's configuration and the role of a potential switch or diode.

Discussion Status

The discussion includes various interpretations of the circuit setup and the behavior of the capacitor. Some participants provide reasoning for their conclusions, while others raise questions about the initial conditions and the assumptions made regarding the circuit elements.

Contextual Notes

There is mention of a gap in the circuit that may be intended to be bridged by a switch, and the orientation of the voltage source is noted as potentially affecting the behavior of a diode in the circuit. Additionally, the discussion touches on the initial charging behavior of the capacitor.

pyroknife
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The problem asks to find the steady state voltage across the capacitor. i attached the circuit (sorry for the poorly drawn and yes, that open part of the branch is supposed to be there) This is a multiple choice question where the answers are:
a) 0V
b) V_dc/2
c) V_dc/3
d) V_dc
e) 2*V_dc

In steady state, a capacitor behaves as an open.
If the capacitor was placed before the resistors, I think its voltage would be V_dc.
However, this capacitor is placed after the resistor.
In steady state, no current will flow through these 2 branches due to the open circuit, thus the voltage drop across the 2 resistors are 0.
This means that the ends of the capacitor are at the same voltage (V_dc). Thus the voltage difference is V_dc-V_dc=0.
So the answer is a. Am I right?
 

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pyroknife said:
The problem asks to find the steady state voltage across the capacitor. i attached the circuit (sorry for the poorly drawn and yes, that open part of the branch is supposed to be there)
I expect that gap is supposed to be bridged by a switch, otherwise the circuit is rather pointless.
 
NascentOxygen said:
I expect that gap is supposed to be bridged by a switch, otherwise the circuit is rather pointless.

The diode used to be where the gap is. But the orientation of the voltage source implies that the diode will become a gap because it will be reverse biased.
 
The capacitor (if it carries any charge) will discharge via the resistor path, until the capacitor voltage reaches zero.
 
NascentOxygen said:
The capacitor (if it carries any charge) will discharge via the resistor path, until the capacitor voltage reaches zero.

Yes. So I think my proof in my first post was correct.

Just for practice, if this was not steady state and the capacitor just began to charge, would its voltage be 0 still? I think that because initially when (time is just greater than 0) a capacitor behaves as a short branch.
 
pyroknife said:
Just for practice, if this was not steady state and the capacitor just began to charge, would its voltage be 0 still? I think that because initially when (time is just greater than 0) a capacitor behaves as a short branch.
Yes, but not for that reason. To change the voltage on a capacitor you have to add charge to it. Adding charge takes time. Immediately after t=0 there has been no time to add much charge, so the voltage across the capacitor plates hasn't changed.
 

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