Electrostatics

In the 1600s and 1700s, electricity was thought to be a liquid. Materials which allowed the liquid to flow through were called conductors. Materials that did not allow the liquid to flow through were called insulators.

Today we know that some materials can hold an electrical charge. We know the charge is not a liquid. Electrostatics is the study of static electricity in materials.

The medium of electrical flow is the electron. Each electron has a negative charge. A material holding a negative charge contains an excess of electrons. A material holding a positive charge contains a lack of electrons. Two materials with like charges repel each other. Two materials with opposite charges attract each other.

Example: If glass is rubbed with silk, the glass gains a positive charge and the silk gains a negative charge.
If we have these two charged glass balls hanging from two strings, the two glass balls would repel each other because both hold a positive charge.

In this tutorial, we will talk about charged points rather than charged object because it is easier to illustrate the distance between charged points. If we had two charged points (each hanging on its own string): one with a positive charge and one with a negative charge, the two charged points would be attracted to each other.

The repulsion and attraction of charged points is very similar to magnetism in that the same general rule applies: opposites attract and likes opposes. A south pole of one magnet is attracted to the north pole of another magnet. The south pole of one magnet is repelled from the south pole of the other magnet.

Figure One shows two charged points. According to Coulomb's Law, the force between the two charged points is proportional to the product of the charges and inversely proportional to the square of the distance between the two charged points.

Force = constant * (charge1*charge2)/(distance²) Equation One

Where

The Force (of attraction or repulsion) is a vector and it's magnitude is measured in newtons,

The constant is a dielectric constant in newton meters squared per coulomb squared

Each charge is measured in coulombs,

And the distance between the two charged points is measured in meters.

This is illustrated in figure one. The force F is the force pushing point q2 away from point q1. The magnitude of the force is determined by equation one.

In the equation in figure one, F is the vector force, q1 and q2 are the charges of the respective charged points and d is the distance between the charged points

Figure two shows three charged points (q1, q2 and q3) and shows how Coulomb's Law is applied.

Figure three shows the three charged points from figure two and shows the resultant forces.

The force F1 is found via applying Coulomb's Law to q1 and q2.

The force F2 is found via applying ohms law to q2 and q3.

The Force F is the result of F1 and F2 as shown in figure four. Hence the Pythagorean Theorem can be applied to find the magnitude of F.

References:
I have a Bachelor of Science in Electrical Engineering.

Understanding Physics
Isaac Asimov
ISBN 0-88029-251-2