1. Electric Forces and Electric Fields
Chapter 18
Electric Forces and Electric Fields

2. 18.1 The Origin of Electricity
Total charge:
where
coulombs

3. 18.1 The Origin of Electricity
Example 1 A Lot of Electrons
How many electrons are there in one coulomb of negative charge?

4. 18.1 The Origin of Electricity
Example 1 A Lot of Electrons
How many electrons are there in one coulomb of negative charge?

5. 18. 1. 1. A brass key has a net positive charge of +1. 92  1016 C
A brass key has a net positive charge of  1016 C. Approximately, how many electrons must be added to the key to make it electrically neutral?
a) 770
b) 960
c) 1200
d) 1800
e) 2100

6. 18.2 Charged Objects and the Electric Force
It is possible to transfer electric charge from one object to another.
The body that loses electrons has an excess of positive charge, while
the body that gains electrons has an excess of negative charge.

7. 18.2 Charged Objects and the Electric Force
Or Silk
Or glass
LAW OF CONSERVATION OF ELECTRIC CHARGE
During any process, the net electric charge of an isolated system remains
constant (is conserved).

8. Complete the following statement: When a glass rod is rubbed with silk cloth, the rod becomes positively charged as
a) negative charges are transferred from the rod to the silk.
b) negative charges are transferred from the silk to the rod.
c) positive charges are created on the surface of the rod.
d) positive charges are transferred from the silk to the rod.
e) positive charges are transferred from the rod to the silk.

9. 18.2 Charged Objects and the Electric Force
Like charges repel and unlike
charges attract each other.