1. Electric Charge O All ordinary matter contains both positive and negative charge. O You do not usually notice the charge because most matter contains the exact same number of positive and negative charges. O An object is electrically neutral when it has equal amounts of both types of charge.

2. Electric Charge O Objects can lose or gain electric charges. O The net charge is also sometimes called excess charge because a charged object has an excess of either positive or negative charges. O A tiny imbalance in either positive or negative charge on an object is the cause of static electricity.

3. Electric Charge O Electric charge is a property of tiny particles in atoms. O The unit of electric charge is the coulomb (C). O A quantity of charge should always be identified with a positive or a negative sign.

4. Electric Forces O Electric forces are created between all electric charges. O Because there are two kinds of charge (positive and negative) the electrical force between charges can attract or repel.

5. Electric Forces O The forces between the two kinds of charge can be observed with an electroscope.

6. Electric Forces O Charge can be transferred by conduction.

7. Electric Current O Current is the movement of electric charge through a substance. Current (amps) Charge that flows (coulombs) Time (sec) I = q t

8. Calculate Current O Two coulombs of charge pass through a wire in five seconds. O Calculate the current in the wire.

9. Coulomb's Law O Coulomb’s law relates the force between two single charges separated by a distance. Force (N) Constant 9 x10 9 N. m 2 /C 2 Distance (m) F = K q 1 q 2 r 2 Charges (C)

11. Coulomb's Law O The force between two charges gets stronger as the charges move closer together. O The force also gets stronger if the amount of charge becomes larger.

12. Coulomb's Law O The force between two charges is directed along the line connecting their centers. O Electric forces always occur in pairs according to Newton’s third law, like all forces.

13. Coulomb's Law O The force between charges is directly proportional to the magnitude, or amount, of each charge. O Doubling one charge doubles the force. O Doubling both charges quadruples the force.

14. Coulomb's Law O The force between charges is inversely proportional to the square of the distance between them. O Doubling the distance reduces the force by a factor of 2 2 = (4), decreasing the force to one- fourth its original value (1/4). O This relationship is called an inverse square law because force and distance follow an inverse square relationship.

15. Calculating Force O Two balls are each given a static electric charge of one ten-thousandth (0.0001) of a coulomb. O Calculate the force between the charges when they are separated by one-tenth (0.1) of a meter. O Compare the force with the weight of an average 70 kg person.

16. Fields and Forces O The concept of a field is used to describe any quantity that has a value for all points in space. O You can think of the field as the way forces are transmitted between objects. O Charge creates an electric field that creates forces on other charges.

17. Fields and Forces O Mass creates a gravitational field that exerts forces on other masses.

18. Fields and Forces O Gravitational forces are far weaker than electric forces.

20. Drawing the Electric Field

21. Electric Fields and Electric Force O On the Earth’s surface, the gravitational field creates 9.8 N of force on each kilogram of mass. O With gravity, the strength of the field is in Newton per kilogram (N/kg) because the field describes the amount of force per kilogram of mass.

22. Electric Fields and Electric Force O With the electric field, the strength is in Newton per coulomb (N/C). O The electric field describes the amount of force per coulomb of charge.