C=q/v

[MedPR]

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Why doesn't increased voltage increase capacitance? If you have higher voltage, doesn't that mean more current assuming constant resistance? And if you pump more current through a capacitor, shouldn't the capacitor then be able to hold more charge?

I mean, I understand that if voltage is conducted across the two plates of a capacitor, that the capacitance goes down, but I don't know why the voltage conducted from the battery through the wires wouldn't increase capacitance.

If you poke a hole in a 50mL cup and pour water in it, the cup's capacity will be less than 50mL.

If you pour 40mL into a 50mL cup, it will only hold 50mL. If you increase how much you pour though, the cup will be able to hold up to 50mL. Isn't this the same as increasing the voltage from the battery?

 

[milski]

You need some rest, some of your ideas about cups are disturbing. 😉 Or most likely - typos.

The analogy between a cup and a condenser is a reasonably good one. You have to keep in mind that if there is no current flowing through it you are always talking about a cup with no hole in it. It does not matter how fast you pour the water in it - it will hold exactly the same amount every time.

If there is a leak: If the water is draining faster than you pour it, the cap will be able to take an infinite amount of water without overflowing. When you stop adding water, it will be empty (almost immediately).

If the water is draining slower, you will eventually fill the cup and then you'll be able to add water at the rate at which it is draining. When you stop adding, for a short period the cup will be holding its nominal amount - same as full cup.

 

[MedPR]

You need some rest, some of your ideas about cups are disturbing. 😉 Or most likely - typos.

The analogy between a cup and a condenser is a reasonably good one. You have to keep in mind that if there is no current flowing through it you are always talking about a cup with no hole in it. It does not matter how fast you pour the water in it - it will hold exactly the same amount every time.

If there is a leak: If the water is draining faster than you pour it, the cap will be able to take an infinite amount of water without overflowing. When you stop adding water, it will be empty (almost immediately).

If the water is draining slower, you will eventually fill the cup and then you'll be able to add water at the rate at which it is draining. When you stop adding, for a short period the cup will be holding its nominal amount - same as full cup.

I meant that if you only had 40mL of water, you couldn't fill the cup to it's capacity. If you had more water (voltage), you could fill the cup to capacitance. I'm not seeing how it isn't the same with voltage. If you pour more and more water into the cup, it will eventually reach max capacity, but if you don't pour enough, it will never reach max capacitance.

 

[milski]

I meant that if you only had 40mL of water, you couldn't fill the cup to it's capacity. If you had more water (voltage), you could fill the cup to capacitance. I'm not seeing how it isn't the same with voltage. If you pour more and more water into the cup, it will eventually reach max capacity, but if you don't pour enough, it will never reach max capacitance.

Voltage (or more proper - potential) in no way determines the amount of charge that is going to flow. Voltage in your water analogy will be from how high you're pouring the water, not how much water you have to pour. You can consider in both cases to be pouring from a hose connected to a huge reservoir.

Voltage/potential describes how much a charge 'wants' to move between two points. It does not tell you anything about the amount of charges at either place or moving between the two points. If you wanted to make an analogy with gravity, you could say that your kitchen table has a "gravity voltage/potential" of 1 m. The gravity does not really care if you put a tiny pin or a huge stone on your table - the potential energy to move any of them from the floor to the kitchen will be weight*1m or weight * "gravity voltage".

 

[MedPR]

Does increased current lead to increased capacitance?

 

[milski]

Does increased current lead to increased capacitance?

No. Capacitance is property of the condenser itself, not of the way you charge it. You will charge it faster with higher current.

I might have an idea what's confusing you. You have to be careful with the water analogies - capacitance is characteristic that tells you how much energy you can store, not how much charge. If you charge the capacitor at higher voltage it will hold more charge and more energy. That does not mean that its capacitance has changed. The capacitance is the ration of the charge and voltage and will stay the same.

 

[MedPR]

No. Capacitance is property of the condenser itself, not of the way you charge it. You will charge it faster with higher current.

I might have an idea what's confusing you. You have to be careful with the water analogies - capacitance is characteristic that tells you how much energy you can store, not how much charge. If you charge the capacitor at higher voltage it will hold more charge and more energy. That does not mean that its capacitance has changed. The capacitance is the ration of the charge and voltage and will stay the same.

Yes, I think that's why I was confused. It makes sense now. Thanks!