A capacitor is connected to a battery for a long time, so it is fully charged. The battery is then disconnected from the capacitor. Then, a conducting wire is used to connect the two plates of the capacitor. Which of the following will happen?
A. The charges on the two plates will annihilate each other, and the voltage will become zero.
B. The charges on the two plates will remain unchanged, but the voltage will become zero.
C. The charges on the two plates will become zero, but the voltage will remain unchanged.
D. Both the charges and the voltage will remain unchanged.

Question

A capacitor is connected to a battery for a long time, so it is fully charged. The battery is then disconnected from the capacitor. Then, a conducting wire is used to connect the two plates of the capacitor. Which of the following will happen?
	A.	The charges on the two plates will annihilate each other, and the voltage will become zero.
	B.	The charges on the two plates will remain unchanged, but the voltage will become zero.
	C.	The charges on the two plates will become zero, but the voltage will remain unchanged.
	D.	Both the charges and the voltage will remain unchanged.

ookawaiioo · Answer

D, The plates are fully charged = no current will be induced. 

C*V = q(max)

anonymous · Answer

A, this will cause a short in the capacitor and will cause current to flow from the charged plate to the uncharged plate. Usually if you do this in real life and with high voltage, the conducting wire gets really hot from the high current or the capacitor explodes.

anonymous · Answer

This is what I'm talking about! http://www.youtube.com/watch?v=bavMk3a8qfk

theeric · Answer

I agree with jenxin. Option A looks best, but there is no annihilating going on. It's just that the electric field is about $\vec 0$ when electrons and protons are together.

Electrons are the charged particles that move around. And electrons are most often said to have negative charge. When the capacitor is charged, one side is full of them, and the other side doesn't have so many (leaving the protons alone so that it's a positive charge).

All that is needed to make the charges do that is the voltage!

Now, electrons will repel each other. And they'll be attracted to the protons. So, take away the voltage and find a way to connect the two sides, and then you'll have a rush of electrons moving to the other side.

The electrons move so they're evenly spread out, without the voltage. And, if the charge is even across the whole thing, the charge will be about $0$.

theeric · Answer

And oOKawaiiOo stated that $C\ V=Q$, or capacitance times the applied voltage is the magnitude of the charge on one side. If the applied voltage is $0$, you can see that the charge that the capacitor will hold is $0$.