13.1. The Big Idea http://www.ck12.org
13.1 The Big Idea
Conservation of chargeis the fourth of the five conservation laws in physics. There are two types of charge: positive
and negative; the law of conservation of electric charge states that the net charge of the universe remains constant.
As with momentum and energy, in any closed system charge can be transferred from one body to another and can
move within the system but cannot leave the system.
Electromagnetismis associated with charge and is a fundamental force of nature, like gravity (which for us is
associated with mass). If charges are static, the only manifestation of electromagnetism is theCoulomb electric
force.In the same way the gravitational force that an object exerts upon other objects, and that other objects exert
on it, depends on the amount of mass it possesses,the Coulomb electric forcethat an object experiences depends
on the amount ofelectric chargethe object possesses. 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 —allof these forces arise in the mutual attraction and
repulsion of charged particles.
Although the law determining the magnitude of the Coulomb electric force has the same form as the law of gravity,
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 opposite
types of electric charge, gravity will dominate in large bodiesunless there is a separation of charge.