There are three main types of charges ◦ Charging by Friction

◦ Charging by Contact

◦ Charging by Induction

Have you ever walked across the room, touched a doorknob and received a shock? ◦ This was the result of an electrostatic charge.

◦ Whenever two materials rub against each other it is likely that one material will leave with more electrons than it started with, the other with less.

◦ Link

Some materials are very greedy and always steal electrons from things they come in contact with and others are more willing to give them up.

We can figure out which one will take and which one will give by using the electrostatic series (p. 275)

The higher up on the list the material is the more it wants to lose electrons so it ends up having a positive charge. The lower it is on the list the more it wants to gain electrons so it ends up with a negative charge.

Remember the example of the man rubbing his feet on the carpet and then touching the doorknob? ◦ Charging by Friction – When his feet rubbed against

the carpet.

◦ Charging by Contact – When he touched the doorknob.

Charging by Friction occurs when two objects are neutral and charges are made by the friction.

Charging by Contact occurs when one object is charged and the other is neutral.

Sometimes a charge can be transferred without actual contact; it just takes the two materials getting close together.

Diagram Explanation

1. A negatively charged rod moves close to a neutral block.

2. The positive charges in the block move closer to the end by the negatively charged rod.

3. The negative charges in the block move away from the rod.

An electrical insulator is a substance in which electrons cannot move freely from atom to atom.

If an insulator gets charged with extra electrons they will stay until something with a stronger force takes the electrons.

If you touch an insulator you can get a very big shock because of the large build up.

◦ Ex. Cars have paint and wax on them which are

both good insulators. When the air rushes over the car when it’s driving a charge is build up. You get out of the car and ZAP!

Charge can’t go through insulators though so they can be very helpful. ◦ Ex. Cord on a kettle – The electricity flows in the

wire that is wrapped in a material that is an insulator. When you touch the cord you don’t get a shock because the electricity cannot travel through the material.

A conductor is a substance in which electrons can move freely from one atom to the other.

If a conductor gets charged the charges can move freely along the material.

The wire in side the kettle is a conductor and the electric charge can travel from the plug all the way to the kettle which uses it.

There are two main ways that we discharge an object. ◦ Grounding

◦ Discharge at a point

Connect a charged object to the ground.

The electric charge can travel from the object and into the earth.

Electrons build up on an object and continuously repel each other. When they repel each other they get pushed off the point.