# Excess charge on insulators and conductors

• Ruby_338
In summary, excess charge on an insulator stays in one place while on a conductor it spreads uniformly due to the presence of mobile charges. This can be explained by the fact that conductors have mobile charges, while insulators do not. These mobile charges tend to move away from each other and follow the electric field, causing the excess charge to spread uniformly on the surface of a conductor.
Ruby_338
From what I've learned, excess charge on an insulator stays where it is but excess charge on a conductor spreads uniformly throughout its surface. Why does this happen? Can this be explained in terms of electrostatic potential?

Ruby_338 said:
From what I've learned, excess charge on an insulator stays where it is but excess charge on a conductor spreads uniformly throughout its surface. Why does this happen? Can this be explained in terms of electrostatic potential?

Sure! Under static condition, what is the electric field inside an idealized conductor?

Zz.

I mean, why doesn't it stay in one place like in an insulator?

Ruby_338 said:
I mean, why doesn't it stay in one place like in an insulator?

Do you know what makes a conductor a conductor, and an insulator and insulator? The amount of mobile charges in it! Insulators do not have any (or many) mobile electrons (or holes), while a conductor/metal, by definition has these things called "conduction electrons" which can move around very easily and are not tied to any particular sites in the conductor.

When there are mobile charges, they tend to move as far away from one another as possible, AND, they tend to follow where there are, if any, electric fields. It is why I asked if you know what is the electric field inside a conductor under static condition.

Zz.

Dale and Ruby_338
I see. Thanks.

## 1. What is the difference between a conductor and an insulator?

A conductor is a material that allows the flow of electric current, while an insulator is a material that does not allow the flow of electric current. Conductors have a high number of free electrons, while insulators have very few.

## 2. Why do insulators have excess charge on their surface?

Insulators have excess charge on their surface because they are not able to conduct electricity, so the charge cannot flow through the material. This causes the charge to accumulate on the surface of the insulator.

## 3. How does the excess charge on conductors and insulators affect their properties?

The excess charge on conductors can be easily distributed throughout the material, while on insulators, the charge stays on the surface. This affects their properties such as their ability to conduct electricity and their surface tension.

## 4. What causes insulators to become charged?

Insulators can become charged due to friction, where electrons are transferred from one object to another. They can also become charged due to induction, where an external electric field causes the movement of electrons within the insulator.

## 5. How is the excess charge on insulators and conductors measured?

The excess charge on insulators and conductors can be measured using an electroscope or an electrometer. These instruments can detect the presence and magnitude of electric charge on a surface.

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