ELECTRIC CHARGE

1. Charge

Some objects have a scalar property called CHARGE. Charge can be either POSITIVE (denoted by "+"), or NEGATIVE (denoted by "-").

Objects which have LIKE charges REPEL one another.

Objects which have UNLIKE charges ATTRACT one another.

The SYMBOL for the charge on an object is Q (or q), and the UNIT OF CHARGE is the COULOMB, (C).

2. Coulomb's law

Two charges will exert a force on each other (either a force of attraction or a force of repulsion, depending on the charges). This force was investigated by Coulomb, who formulated what is now known as Coulomb's Law:

Coulomb's Law
"The magnitude of the electric force between two point charges is directly proportional to the product of the charges and inversely proportional to the square of the distance between them."

Referring to the diagram on the right, this means that if we have two point charges, Q1 and Q2, separated by a distance r, then

In the above equation, the constant of proportionality, k, is a fundamental physical constant called COULOMB'S CONSTANT, which has the value of 9.00 x 109 N·m2·C-2.


3. Conservation of charge

Charge can be transferred from one object to another. The algebraic sum of the charges on the two objects will be the same before and after the transfer. (This is sometimes called the Law of Conservation of Charge, discovered by Benjamin Franklin).

Law of Conservation of Charge
"The total charge of any isolated system is constant and independent of changes that take place within the system ."

If Q1 and Q2 are the charges on two objects 1 and 2, then if a transfer of charges takes place without external influences, and the new charges are Q1' and Q2', then

The subatomic particle which has a single positive charge is called the PROTON. Its charge is 1.60210 x 10-19 C.

The subatomic particle which has a single negative charge is called the ELECTRON. Its charge is -1.60210 x 10-19 C.


4. Additional questions