Potential difference across capacitor in a network

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Homework Help Overview

The discussion revolves around determining the potential difference across the plates of a capacitor within a network, utilizing Kirchhoff's loop rule and the relationship between charge, voltage, and capacitance.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants explore the application of Kirchhoff's law and the implications of the equations related to charge and capacitance. Questions arise regarding the signs of the potential differences and the assumptions about reference points in the circuit.

Discussion Status

There is an ongoing exploration of different interpretations regarding the potential differences across the capacitor plates. Some participants suggest that the question may be poorly worded, while others discuss the implications of defining ground potential and the resulting polarity of voltages.

Contextual Notes

Participants note that the question's wording may lead to confusion, and there is a reference to the context of an examination setting where such ambiguities can affect student responses.

Suyash Singh

Homework Statement


Determine the potential difference across the plates of the capacitor of the network shown in the figure.

6cfd021e59d9eff49396f757df312d4af4ab835d.png

Homework Equations


kirchoff's loop rule
q=vc
3. The attempt at a solutio
applying kirchhoffs law
starting at bottom right point,
q/c2-E1+q/c1+E2=0
=>E2-E1=-q/c1-q/c2
now i am confused what to do further

the answer is
V1=-q/c1 and V2=q/c2
 
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You don't need Kirchoff's law. Look at the second of the two relevant equations that you wrote down. Give q and c, what is v?
 
phyzguy said:
You don't need Kirchoff's law. Look at the second of the two relevant equations that you wrote down. Give q and c, what is v?
v=q/c
but why is v1 negative and v2 positive?
 
Suyash Singh said:
v=q/c
but why is v1 negative and v2 positive?
Negative or positive with respect to what?
Looks like they are assuming the ground to be at the negative terminal of E2.
 
+1

I think it is a badly written question. Is that the exact wording?
 
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CWatters said:
+1

I think it is a badly written question. Is that the exact wording?
yes it was asked in All India CBSE board 2013.
 
cnh1995 said:
Negative or positive with respect to what?
Looks like they are assuming the ground to be at the negative terminal of E2.
the ground is taken at zero potential in our syllabus.
 
Even if the 0V node was specified the polarity of the voltages isn't defined. Consider this circuit...

Polarity.png


If E1 = 10V then V3 = 10V and V2 = -10V. See how the polarity depends on the direction of the arrow I drew on the circuit.

So I would argue that in your circuit all of the following are valid answers...

V1=+q/c1 and V2=+q/c2
V1=-q/c1 and V2=+q/c2
V1=+q/c1 and V2=-q/c2
V1=-q/c1, and V2=-q/c2
 
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