What does a capacitor actually do? Does it store electrical energy or

[Science Proff]

What does a capacitor actually do? Does it store electrical energy or does is store charge?
Please Explain.

 

[timthereaper]

It stores charge. A capacitor in its simplest form is two plates separated by a distance so that they don't touch. When you connect a capacitor to a voltage source, the electrons collect on one plate. The negative charge of the plate repels electrons on the other plate and causes current to flow on the other side of the capacitor. However, the plate can only store a certain amount of charge (limited by the voltage of the source) and once the other plate attains an equal net positive charge, eventually the voltage on the other side of the circuit dies out. The charge that is built up on the plate is a form of stored energy, so you could say the capacitor stores energy, but the energy is in the form of charge.

This is at least the way I got it explained to me in my Intro to EE class.

 

[vanhees71]

The energy stored by the capacitor in fact is the energy of the electric field between the plates!

This becomes an even more interesting example if you ask about the mass change of the capicitor between a charged and an uncharged state and what happens for a moving capacitor!