Electrification - the process that produces electric charges on an object. Electrostatic charge - a charge confined to an object and not moving. Static electricity - stationary electricity in the form of an electric charge at rest.

A neutral object has a net charge of zero, equal numbers of positive and negative charges.

The Basic Law of Electrostatics Objects that are similarly charged repel each other; objects that are oppositely charged attract each other.

Electron mass: x kg Proton mass: x kg Neutron mass: x kg

Protons and neutrons are bound together by the strong nuclear force. Net charges are the result the transfer of electrons.

A positive charge is a net deficiency of electrons. A negative charge is a net excess of electrons.

Electroscope - a device used to detect electric charge. Aluminum vane - a light aluminum rod is deflected by electrostatic repulsion. Gold leaf - a fragile strip of gold leaf is deflected when charged.

A proof plane is a small metal disk with an insulating handle. The proof plane can be used to transfer a charge to an electroscope by touching the charged object and then the electroscope.

Touching the proof plane to a previously charged electroscope can determine an unknown charge. Like charge will increase the deflection, an opposite charge will decrease the deflection.

A conductor is a material through which an electric charge is readily transferred. An insulator is a material through which an electric charge is not readily transferred.

Metals have a crystal lattice composed of positively charged particles surrounded by a cloud of free electrons. This cloud of electrons is called the electron gas. These electrons are free to move throughout the lattice and are responsible for the metal’s high conductivity.

An insulator has few free electrons because all electrons are held tightly in the crystal lattice.

If a charged object is held close to a neutral object, the neutral object acquires a temporary opposite charge.

When a negatively charged object is held near an electroscope, no charge is transferred. If a path is provided for electrons to escape the electroscope while the repelling force is present, they will do so.

If the escape path is then removed before the repelling force is removed, the electroscope is left with a net positive residual charge. The same can be done with a positively charged source to produce a negative residual charge.

This is called an induced charge. The process is called induction.

When an isolated conductor is given a residual charge by induction, the charge is opposite in sign to that of the object inducing it.

When a charged object is touched to a neutral object, the charge is transferred by conduction. The two charges are the same as the original.

Any conducting object, properly isolated in space and charged by conduction, acquires a residual charge of the same sign as that of the body touching it.

If a charge is evenly dispersed over a sphere, the effect is such that the charge emanates from the center, thus it is called a point charge.

The quantity of charge on a body,q, is measured in coulombs. A coulomb is equal to the charge on 6.25 x electrons.

An electron has a charge of 1.60 x C. The sign of Q is -. A proton has a charge of 1.60 x C. The sign of Q is +.

The coulomb is a large unit, so the microcoulomb (  C) is often used. 1  C = C

Force Between Charges Coulomb found that the force between two point charges is directly proportional to the product of their magnitudes and inversely proportional to the square of the distance between them.

This is called Coulomb’s Law of Electrostatics. F is proportional to q 1 q 2 /d 2

A proportionality constant can be added to make this an equation. F = k q 1 q 2 /d 2

k is called the electrostatic constant. k is x 10 9 for a vacuum, and 8.93 x 10 9 for air. (We will use 9 x 10 9.) k is in Nm 2 /C 2. q 1 and q 2 are in coulombs. d is in meters, and F is in newtons.

Two one coulomb charges are separated by 1 meter. What is the force between them?

A +5  C charge and a -6  C charge are separated by a distance of 0.5 m. What is the force between the two charges?

Two electrostatic charges of 60.0  C and 50.0  C exert a repulsive force on each other of 175 N in air. Calculate the distance between the two charges.