1. Electrostatics

2. Insulators and Conductors
In insulators, electrons are bound in “orbit” to the nucleus in each atom.
When charge is placed on an insulator, it stays in one region and does not distribute.
Wood, plastic, glass, air, and cloth are good insulators.
Conductors
CHARGED INSULATOR
In conductors electrons can move from atom to atom, thus electricity can “flow”.
When charge is placed on a conductor, it redistributes to the outer surface.
Metals (copper, gold, and aluminum) are good conductors.
CHARGED CONDUCTOR

3. Polarization Polarization is the separation of charge
In a conductor, “free” electrons can move around the surface of the material, leaving one side positive and the other side negative.
In an insulator, the electrons “realign” themselves within the atom (or molecule), leaving one side of the atom positive and the other side of the atom negative.
Polarization is not necessarily a charge imbalance!

4. Charging by Friction
POSITIVE
Rabbit's fur
Glass
Mica
Nylon
Wool
Cat's fur
Silk
Paper
Cotton
Wood
Lucite
Wax
Amber
Polystyrene
Polyethylene
Rubber ballon
Sulfur
Celluloid
Hard Rubber
Vinylite
Saran Wrap
NEGATIVE
When insulators are rubbed together, one gives up electrons and becomes positively charged, while the other gains electrons and becomes negatively charged.
Materials have different affinities for electrons. A triboelectric series rates this relative affinity.
A material will give up electrons to another material below it on a triboelectric series.
Common examples of charging by friction:
• small shocks from a doorknob after walking on carpet with rubber-soled shoes
• plastic foodwrap that sticks to a container
• sweater pulled over your head that sparks
• laundry from the dryer that clings
• balloon rubbed with hair sticks that to a wall

5. Charging by Conduction
When a charged conductor makes contact with a neutral conductor there is a transfer of charge.
CHARGING NEGATIVELY
CHARGING POSITIVELY
Electrons are transferred from the rod to the ball, leaving them both negatively charged.
Electrons are transferred from the ball to the rod, leaving them both positively charged.
Remember, only electrons are free to move in solids.
Notice that the original charged object loses some charge.

6. Charging by Induction
Induction uses the influence of one charged object to “coerce” charge flow.
Step 1. A charged rod is brought near an isolated conductor. The influence of the charge object polarizes the conductor but does not yet charge it.
Step 2. The conductor is grounded to the Earth, allowing charge to flow out between it and the Earth.

7. Charging by Induction (cont.)
Step 3. The ground is removed while the charge rod is still nearby the conductor.
Step 4. The rod is removed and the conductor is now charge (opposite of rod).
An object charged by induction has the opposite sign of the influencing body.
Notice that the original charged object does not lose charge.

8. Charge Smallest charge unit: charge of 1 electron
1 electron = x10-19Coulomb