The Big Idea
Conservation of charge is the fourth of the five conservation laws in physics. There are two charges, positive and negative, and the conservation of electric charge indicates that the total charge in the universe remains the same. In any closed system charge can be transferred from one body to another or can move within the system but the total electric charge remains constant.
Electromagnetism is associated with charge and is a fundamental force of nature, like gravity. If charges are static, the only manifestation of electromagnetism is the Coulomb electric force. In the same way that gravitational force depends on mass, the Coulomb electric force depends on the property known as electric charge. Like gravity, the Coulomb electric Force decreases with the square of the distance. The Coulomb electric force is responsible for many of the forces we discussed previously: the normal force, contact forces such as friction, and so on - all of these forces arise in the mutual attraction and repulsion of charged particles.
The law determining the magnitude of the Coulomb electric force has the same form as the law of gravity. However the electric constant is 20 orders of magnitude greater than the gravitational constant. That is why electricity normally dominates gravity at the atomic and molecular level. Since there is only one type of mass but two types of charge, gravity will dominate in large bodies unless there is a separation of charge.
The lessons in this chapter cover electrostatics at a conceptual level as well as a detailed mathematical approach using Coulomb's Law. Electric fields are covered. Voltage, electric potential lines and energy problem solving techniques are also covered.