1. Ch. 32 Electrostatics Electricity at rest

2. Electric Forces Arise from subatomic particles – Positive nucleus surrounded by negative electrons Charge: physical property that causes particles to experience a force 2 TYPES: Positive Negative

5. Conservation of Charge Since matter is neither created nor destroyed, subatomic particles are neither created not destroyed. Subatomic particles may be transferred from one object to another, but overall, charge is conserved!!!

6. Standard unit of Charge Coulomb (C ) The charge of an electron is 1.6 x 10 -19 C

7. A pair of identical coins are electrically charged. One with a charge of + 15  C and the other a charge of – 8  C. When they are brought together, what is the charge of each after contact? Net Charge = + 15  C – 8  C = 7  C The coins are identical, therefore they will share the charge equally. 3.5  C charge for each coin!

8. Coulomb’s Law The force between the charges is directly proportional to the product of their charges and inversely proportional to the distance between F = k q 1 q 2 k= constant = 9 x10 9 N m 2 d 2 C 2 q 1 = charge 1 q 2 = charge 2 d = the distance between q 1 & q 2

9. F = k q 1 q 2 d 2 q1q1 q2q2 d k = 9.0 x 10 9 N  M 2 /C 2 What other equation does this remind you of????

10. Practice Problem F = k q 1 q 2 d 2 What is the electrostatic force between a pair of electrons 1 m apart? k = 9.0 x 10 9 N  M 2 /C 2 The charge of an electron is 1.6 x 10 -19 C

11. Practice Problem F = k q 1 q 2 d 2 What is the electrostatic force between a pair of electrons 1 m apart? k = 9.0 x 10 9 N  M 2 /C 2 The charge of an electron is 1.6 x 10 -19 C F = (9.0 x 10 9 N  M 2 /C 2 ) (1.6 x 10 -19 C) (1.6 x 10 -19 C) (1 m) 2 F = 2.3 x 10 -28 N

12. What is the electrostatic force between a 5 x 10 -6 C charge and a 3 x 10 -8 C charge that are 0.25 m apart?

13. F = k q 1 q 2 d 2 F =

14. What is the electrostatic force between a 5 x 10 -6 C charge and a 3 x 10 -8 C charge that are 0.25 m apart? F = k q 1 q 2 d 2 F = (9.0 x 10 9 N  m 2 /C 2 ) (5 x 10 -6 C )(3 x 10 -8 C ) (0.25 m) 2 = 0.0216

15. Conductors & Insulators

16. Charging 3 Methods that result in charging: – Friction – Contact – Induction

17. Charging Friction: When electrons are transferred by friction from one object to another Contact Induction

18. Charging Friction Contact: when electrons are transferred from one object to another by direct contact Induction

19. Charging Friction Contact Induction: when electrons are caused to move by the presence of a nearby charge.

20. Charge Polarization Occurs in insulators Rearrangement of the positions of charges within the atoms and molecules

21. The End In Class: Practice Problem Solving with coulomb’s Law