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Basic Electric Potential Theory

by mcpoopants
Tags: basic, electric, potential, theory
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mcpoopants
#1
Sep28-10, 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.
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zhermes
#2
Oct1-10, 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 wire---between the resistor and capacitor---has a given voltage difference from a point on the bottom wire---between the resistor and cap---across 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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