Capacitor: Cathode/Anode Convention

[justadream]

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I have in my notes that for:

Charged Capacitor:
Cathode: Negative
Anode: Positive


Discharging Battery:
Cathode: Positive
Anode: Negative


What about a DISCHARGING CAPACITOR? What would be the convention here? Is that the same as a charged capacitor?

 

[Cawolf]

I think the best way to think about it is to look for where reduction is occurring. The electrode that is receiving electrons is being reduced, and is therefore labeled the cathode.

A fully charged capacitor has a highly reduced plate that is negatively charged - cathode.

A discharging capacitor results in electron movement the opposite way of when it was being charged.

The plate with higher electron density (negative charge) will lose electrons that flow towards the positive charge - becoming oxidized, and by convention an anode.

So I would say that the plates of a discharging capacitor are analogous with a cell by charge/name due to the direction of electron flow.

Sorry for the long post, but I have not seen them named before, and this is my way of reasoning it out.

 

[justadream]

@Cawolf

So you're saying a discharging capacitor should be treated like a normal discharging battery.

 

[Cawolf]

Yes. Except that the potential difference is decreasing exponentially instead of remaining constant.

 

[justadream]

@Cawolf

Btw: For the "Charged capacitor", does:
Cathode: Negative
Anode: Positive

apply to BOTH
1) When you are in the process of charging
2) When you have finished charging

 

[Cawolf]

It technically only applies while charging, because when the electrons are stationary (charged), there is no oxidation or reduction occurring. I think it is safe to call it the same as the connection to whatever is charging it is still closed, so the conditions are the same. I think that is how question writers would refer to it as well. They definitely wouldn't switch the nomenclature if discharging has not started.