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Charge Distributions on Insulators & Conductors

Instructor: Betsy Chesnutt

Betsy teaches college physics, biology, and engineering and has a Ph.D. in Biomedical Engineering

Although conductors and insulators can both be charged, the excess charge ends up distributed very differently! In this lesson, learn about how excess charge is distributed on different types of conductors and insulators.

Insulators vs. Conductors

When an object acquires some excess charge, what happens? Does the charge stay where you put it or does it move? Well, that depends on what type of material the object is made of. Certain materials, called conductors, allow electric charge to move pretty freely through them. Most metals are good conductors, so when a metal object is given some charge, it's free to move around. Other materials, like plastic and rubber, are called insulators because they don't allow electric charges to move through them.

Let's take a look inside an insulator and a conductor to see what makes them different. Inside both conductors and insulators, there are many tiny atoms, and inside each atom, there are positively charged protons and negatively charged electrons. Protons are always tightly bound to each other within the nucleus of each atom, so they don't move around in conductors OR insulators. In contrast, electrons are in a cloud around the nucleus. In insulators, all of the electrons are strongly bound to each atom and aren't free to move around from atom to atom. In conductors, some of the electrons are loosely bound to each atom so they can easily move around, allowing charge to flow and redistribute throughout the conductor.

Charge Distribution in a Regularly Shaped Conductor

Conductors allow charges to move around because they have a lot of highly mobile charge carriers (electrons). How do the charges know where to go? Remember that charges that are the same will always repel each other, so if there are excess electrons anywhere in a conductor, they will push away from each other until they get as far from each other as they can.

Where will they end up? Imagine that you're stuck in a room with a bunch of other people and all of you want to get as far away from each other as possible. You can't leave the room, so where do you all go? To the outside walls of the room! You push each other away until you can't go any further. The excess electrons in a negatively charged conductor do exactly the same thing. They push each other away until they all end up on the outer surface. No charges will remain inside the conductor once it reaches equilibrium and the charges stop moving.

If the surface of the conductor is smooth and regular, like a sphere, the charges will push each other away until they all end up exactly the same distance from each other.

Charge will be evenly distributed over the surface of a regularly shaped conductor.
charge distribution on a regularly shaped conductor

Charge Distribution in an Irregularly Shaped Conductor

How does the charge distribution change if the surface of the conductor is NOT smooth and regular? In this case, there will be more charge where the surface curves more sharply and a smaller buildup of charge at locations where the surface is less curved or flat. This buildup of charge on sharp points creates large electric fields near these points, which makes it more likely that sparks will be generated.

Charge is NOT distributed evenly over the surface of an irregularly shaped conductor.
charge distribution on an irregular conductor

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