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Basic Electric Potential Theory 
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#1
Sep2810, 09:05 PM

P: 1

Alright, so there is a very basic theory involving capacitors and electric potential that is throwing me off. I have a very basic problem here: http://img444.imageshack.us/img444/2251/73619554.png
Assume the switch is closed and the capacitor is fully charged. From here I'm prompted to find the final voltage across the capacitor. Pretty obvious, you use V=IR, but I'm missing out on the value of "R". In this problem it is just R2, which is given to you. My problem is that I do not understand how the voltage across that resistor is equivalent to the voltage across that fully charged capacitor. It'd really help to explain as slowly as possible, because it is a basic idea that is kicking my butt in more complicated problems. Thanks to all. 


#2
Oct110, 03:07 PM

P: 1,261

Use kirchoff's loop rule around R2 and the capacitor. When you move from a point in a circuit, back to the same point, the net voltage change must be zero. This is the same thing as saying that the voltage difference between a point and itself is zero.
So, if a point on the top wirebetween the resistor and capacitorhas a given voltage difference from a point on the bottom wirebetween the resistor and capacross the resistor, it has to be the same as across the capacitor.... because they're the same two points. Does that make any sense? 


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