Understanding Capacitors: Polarization and Charge Distribution

[zoner7]

This is not really a homework question; I simply don't understand a property of capacitors.

How come when some emf is attached to a simple circuit with a capacitor in it, the positive charge all gathers on one plate while the negative charge all gathers on the opposite plate? Why is there not an equal distribution of charge? Additionally, why are the positive charges flowing in the wires? When we discussed charged objects, it was only the electrons that were free to move... I need a giant explanation of all of this. i think i lost something along the way.

EDIT: Another quesrion:
I just read this excerpt from the text explaining dielectrics: "Less extreme fields can polarize an atom, in essence stretching it so that its electrons tend to be on one side and its positive nucleus is on the other. This turns the atom into a dipole, a body with positively and negatively charged regions."

If both ends of the capacitor are equally charged, how are we supposed to determine which side the electrons will veer towards and which side the protons will veer towards? Doesn't the dielectric need to be arranged in such a way that the net field is zero?

 

[Delphi51]

A capacitor does not allow charge to flow through. The emf pulls electrons away from one side, and pushes electrons into the other side. So + on one side (shortage of electrons) and - on the other side. Remember, the positive charges in the atomic nuclei are always present and usually canceled out by orbiting electrons. The + charge is attracted to the - charge so the capacitor will remain charged when the emf is taken away.

We often speak of positive or conventional charges flowing because historically for a long time there was no way to tell which charge was flowing and someone guessed it was positive. It hardly ever makes a difference which you use.

The charged capacitor has + on one side, - on the other so there is a strong electric field in the space in between. This field pulls one way on the atomic nucleus and the other way on the electrons, separating their centers slightly. You don't really need the field in the explanation - the electric force due to the positive charge causes this, and the negative charge on the other side doubles it.

 

[nlightner]

I can explain the phenomenon of charge distribution in capacitors and the role of dielectrics in this process.

Firstly, it is important to understand that capacitors are made up of two conductive plates separated by a non-conductive material, known as a dielectric. When an EMF (electromotive force) is applied to the circuit, it creates an electric field between the two plates of the capacitor. This electric field causes a separation of charges within the capacitor, with positive charges accumulating on one plate and negative charges on the other.

This unequal distribution of charges is a result of the properties of the dielectric material. Dielectrics are insulators, meaning they do not allow the flow of electrons. However, they can become polarized when placed in an electric field, meaning that the atoms within the dielectric material are slightly shifted, with the positive and negative charges being separated. This creates an opposing electric field within the dielectric, which counters the external electric field and leads to the separation of charges in the capacitor.

Now, to address your question about the flow of positive charges in the wires. As you mentioned, in our discussion of charged objects, it is only the electrons that are free to move. However, in a capacitor, the flow of charges is not through the dielectric material, but rather through the conductive plates and the wires connecting them. The positive charges on one plate will repel the positive charges in the wire, causing them to move towards the other plate, creating a flow of positive charges in the wire.

As for the role of dielectrics in determining the direction of charge flow, it is important to note that the dielectric material does not determine the direction of charge flow. It is the external electric field that determines the direction of charge separation and thus the direction of charge flow in the capacitor.

To address your second question about the arrangement of dielectrics, it is true that in order to have a net electric field of zero, the dielectric material needs to be arranged in a specific way. This is known as a "parallel plate capacitor," where the dielectric material is placed between two parallel plates with the same surface area. In this arrangement, the opposing electric fields created by the dielectric material cancel out, resulting in a net electric field of zero.

In summary, the unequal distribution of charges in a capacitor is a result of the properties of the dielectric material and the external electric field. The role