# I Help clarifying capacitors, dielectrics, E field, potential

1. May 21, 2017

### Notaphysicsmajor

Hello there,

I was wondering if anyone wouldn't mind helping clarify what is occurring with a charged capacitor for me.

I understand that in a charged capacitor one conducting plate is negatively charged and one is positively charged due to the distribution or rearrangement of electrons. There is then an electric field that occurs in the space between the two plates, as well as potential energy.

Now perhaps I just need a quick review, but what's the difference between the electric field and the potential energy? I know that the electric field is force, and that potential energy is work, but what does that exactly mean? To me, electric field means that it is the force that will be applied to another charge if it were present. Potential energy is the amount of work done on a charge moving it from one position to another. Is this correct?

Now with dielectrics, I understand through the equation on why a dielectric or insulator increases the capacitance, but how does this do this exactly from a physics stand point? I understand that due to the differently charged capacitor plates there is an electric field that transpires and when the dielectric is added the charges will rearrange in that the positive ends will point towards the negatively charged capacitor plate while the negativel ends will be facing the positive capacitor plate. Is it because of the extra charges on the dielectric that allow the capacitor to hold more charges onto it due to the fact that it allows more charges to accumulate onto the capacitor plates since it will be able to pair or have an attraction with the charges on the dielectric? How does this affect the electric field and potential?

2. May 21, 2017

### Staff: Mentor

The electric field is the gradient of the potential: $E=-\nabla \phi$

3. May 21, 2017

### Chandra Prayaga

The electric field is not a force. Force is a push or a pull which is exerted on an object. The electric field is a vector that exists at every point in space. Suppose you choose a point anywhere, and the elctric field vector there is E. If you place a point charge q there, the force on the point charge is qE. If you place a different point charge there, the force will be different, even though the electric field is the same.
The change in electric potential energy is the negative of the work done by the electric force on the charge as the charge moves from one point to another.