Potential difference across capacitor in a network

[Suyash Singh]

Homework Statement

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

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

 

[phyzguy]

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?

 

[Suyash Singh]

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?

 

[cnh1995]

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.

 

[CWatters]

+1

I think it is a badly written question. Is that the exact wording?

 

[Suyash Singh]

+1

I think it is a badly written question. Is that the exact wording?

yes it was asked in All India CBSE board 2013.

 

[Suyash Singh]

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.

 

[CWatters]

Even if the 0V node was specified the polarity of the voltages isn't defined. Consider this circuit...

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

 

[Suyash Singh]

thanks guys.I think the question maybe wrong.It happens frequently and all depends on the student's luck in such cases as examiners do not use their own brain and just compare with the model answers provided to them.

http://www.hindustantimes.com/educa...om-68-to-95/story-NTupvC1xJIS86FWv7bnZzN.html