## Voltage over a capacitor in a RC-circuit.

Why is the voltage over the parallel-connection containing the capacitor Vc= Q/C

It makes a little (intuitive) sense to me, but I would like to see the proof if possible. Thanks.
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 Why is the voltage over the parallel-connection containing the capacitor Vc= Q/C
Are you asking...
1) why is the voltage on the capacitor = Q/C?
or
2) why is the voltage on the parallel combination of R and C the same as the voltage on the capacitor alone?

 I'm asking 2.

## Voltage over a capacitor in a RC-circuit.

The voltage must be the same because both components are connected between the same nodes.

 And if you want to know why the voltage must be the same between the same two nodes, the reason is that the only field we're dealing with here is an electric field set up by the charges on the capacitor plates. But an electric field is a conservative field, meaning that if we take a test charge between two points, A and B, in the field, the work done by the field on the charge is the same for whichever route we go from A to B. So the work done on the test charge per unit charge it carries, i.e. the potential difference or voltage, is the same for all routes. In your case the routes of interest are via the capacitor and via the resistor!
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