Consider a simple series RC circuit at steady state (capacitor is full).
I've been told that once the capacitor is full we can literally "cut" the circuit because no current can flow.
That argument makes sense, but because the capacitor is full, doesn't that also mean it has a potential difference across it? In other words, the capacitor is a new battery? Then we should apply Kirchhoff Law in the circuit if we want to find the current? (even though I just said it was zero).
What is going on? What is this contradiction?
There is no current in the circuit yet clearly the potential difference in the capacitor is NOT zero.
I've been told that once the capacitor is full we can literally "cut" the circuit because no current can flow.
That argument makes sense, but because the capacitor is full, doesn't that also mean it has a potential difference across it? In other words, the capacitor is a new battery? Then we should apply Kirchhoff Law in the circuit if we want to find the current? (even though I just said it was zero).
What is going on? What is this contradiction?
There is no current in the circuit yet clearly the potential difference in the capacitor is NOT zero.
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When the battery is first connected, current flows and the capacitor begins to charge. As it charges, the potential difference across the capacitor gradually increases. As it does so, the current flowing into the capacitor gradually decreases, because the potential difference building on the capacitor is approaching the voltage of the battery. When the P.D. across the capacitor reaches the same voltage as the battery, current ceases to flow. At this time you can disconnect the fully charged capacitor from the circuit. No current will flow because there are no longer any connections to the capacitor. However, if you now connect a resistor across the capacitor, current will again flow, gradually decreasing until the capacitor's charge is gone.
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The capacitor isn't really a battery, because the potential difference is due to charge separation, rather than work being done by a chemical reaction. I don't think this is central to your question, though.
I assume that by "cut the circuit", you mean breaking the wire somewhere. If that's the case, then yes, you can use Kirchhoff's Loop Law to find the current. Just remember that the resistance of the break is infinite. So if you apply Kirchoff's Loop Law, you'll get a current of zero, as expected.
(Remember that potential differences only cause currents in resistors. For example, batteries have a potential difference across them as they sit in their packages on the store shelves, but no current is flowing.)
I assume that by "cut the circuit", you mean breaking the wire somewhere. If that's the case, then yes, you can use Kirchhoff's Loop Law to find the current. Just remember that the resistance of the break is infinite. So if you apply Kirchoff's Loop Law, you'll get a current of zero, as expected.
(Remember that potential differences only cause currents in resistors. For example, batteries have a potential difference across them as they sit in their packages on the store shelves, but no current is flowing.)