1. Coulomb’s Law

2. Electric Force Symbol: F el Symbol: F el Definition: the attractive or repulsive force between any 2 charged objects. Definition: the attractive or repulsive force between any 2 charged objects.

3. Coulomb’s Law Used to determine the force of the charge between two objects. Used to determine the force of the charge between two objects. Coulomb found that the force is inversely proportional to the squared distance between the two objects Coulomb found that the force is inversely proportional to the squared distance between the two objects F = 1 / d 2 (look familiar!?!?!?)

4. Coulomb’s Law F el = K x q 1 x q 2 d 2 d 2 F el = force of electric charge (N) F el = force of electric charge (N) K = electrical constant (9.0 x 10 9 Nm 2 /C 2 K = electrical constant (9.0 x 10 9 Nm 2 /C 2 q = amt. of charge on object (measured in Coulombs, C) q = amt. of charge on object (measured in Coulombs, C) d = distance between objects (meters) d = distance between objects (meters) Answer is (-) when force is attractive Answer is (-) when force is attractive Answer is (+) when force is repulsive Answer is (+) when force is repulsive

5. Inverse Square Law F el is proportional to 1/d 2 F el is proportional to 1/d 2 Ex. double distance Ex. double distance F el ’ = 1/ (2) 2 = ¼ F elF el ’ = 1/ (2) 2 = ¼ F el Ex. cut distance in ½ Ex. cut distance in ½ F el ’ = 1/ (1/2) 2 = 1/(1/4) = 4 F elF el ’ = 1/ (1/2) 2 = 1/(1/4) = 4 F el

6. Practice Cut the distance by 1/3 Cut the distance by 1/3 F el increases by 9 timesF el increases by 9 times

7. Coulomb Unit of charge Unit of charge 1C = 6.25 x 10 18 e - 1C = 6.25 x 10 18 e - A bolt of lightening transfers 1-20 Coulmbs A bolt of lightening transfers 1-20 Coulmbs

8. Coulomb’s Law Find F el : Find F el : 3.46 x 10 -4 N 3.46 x 10 -4 N q = 4.80 x 10 -7 Cq = 3.20 x 10 -7 C 2 m