1. Introduction to Forces and Fields
Static Electricity
Introduction to Forces and Fields

2. Ancient Greeks – observed attraction and repulsion between different materials
Matter is composed of atoms
Atoms are composed of protons, electrons and neutrons

3. Static Electricity

4. Present Model
Charge is created by a transfer of electrons, protons cannot move.
Excess electrons produce a negative charge.
Deficit of electrons produces a positive charge.
Neutral objects have equal numbers of electrons and protons

5. Atoms are electrically neutral
Electrons – negative (-)
Protons – positive (+)
Neutrons – no charge
Atomic Structure + n e
Nucleus (p + n)
Note: The charge in an atom (object) is the result of the transfer of electrons

6. An object the becomes negatively charged, gains electrons Eg) atom
10p
10e
12e
neutral
Net charge of -2e (ion)
10p
10e
Loses an e 9e
Net charge of +1 (ion)

7. Law of Conservation of Charge
Total charge within an isolated system remains constant
Charge is conserved (constant)
Objects that become charged result in a transfer of charge (electrons) and charge is neither created nor destroyed

8. Law of Electric Charge 1
There are two kinds of charge, (+) and (-) (neutral is not a charge)
Like charges repel - +
-electrical force of repulsion ( )

9. Law of Electric Charge 2 Unlike charges attract- +
-electrical force of attraction

10. Categories of Materials
1. Conductors
Electrons are free to move in materials such as metals.
An object with excess electrons comes into contact with a conductor
In conductors, electrons are easily transferred so they spread out over the entire object.

11. 2. Insulators
Electrons are not free to move in materials such as plastics and glass
Rubbing ebonite with fur produces a
negative charge on the ebonite
Rubbing glass with silk produces a
positive charge on the glass