The Theory of Electricity All substances are made of protons (positive) and electrons (negative). Undisturbed objects have a neutral charge, since the number of protons and electrons is equal. What is the charge on this object?

Some objects, when rubbed, pick up electrons from the material that is doing the rubbing. As a result the rubbed object becomes negatively charged and the material becomes positively charged.

This table lists materials in order of their electron affinity The tendency of a substance to hold on to electrons is called electron affinity Tend to lose electrons Tend to gain electrons (+) Human skin (dry) Glass Human hair Nylon Cat fur Silk Cotton Steel Wood Amber Ebonite Plastic wrap Teflon (-) This table lists materials in order of their electron affinity

The 3 Laws of Electrical Charges 1) Opposite charges attract each other. 2) Like charges repel each other. 3) Charged objects attract neutral objects.

How do objects become charged? 1. Friction: when object rub against each other

2. Contact: when electrons transfer from the charged object to the neutral object that it touches

3. Induction: the movement of electrons within an object caused by a nearby charged object, without direct contact

Making Use of Static Electricity 1. Spray Painting The paint coming out of the nozzle gains a negative charge through friction… The car is grounded (neutral) – therefore the paint is attracted to the car! Less waste and a smooth finish. Car is grounded because of rubber tires or a ground strap (piece of rubber hanging from the car).

2. Electrostatic Precipitators Particulate matter (PM) passes through a mesh that charges it negatively. Then the PM is attracted to positively charged collecting plates along the smoke stack. Used in industrial plants such as cement, steel and lumber.