1. January 14, 2005Electrostatics1 Lecture 1-3 Charge Completed January 14, 2005

2. Electrostatics 2 Whatsup? Short Quiz Today Complete the topic of Charge There is a WebAssign for this chapter. Chapter 21 should have been read. Next Week  Monday = MLK Holiday  Wed, Fri – the Electric Field (Ch- 22)

3. January 14, 2005 Electrostatics 3

4. January 14, 2005 Electrostatics 4 Quick Review When objects are rubbed together or pulled apart, the two surfaces are found to be CHARGED. Two kinds of Charge –  Positive (The rubber rod after dead cat)  Negative (The glass rod after being rubbed with wool or silk.)

5. January 14, 2005 Electrostatics 5 Charge can be TRANSFERRED OR SEPARATED Contact Induction (With some “Grounding”) Polarization

6. January 14, 2005 Electrostatics 6 That Balloon … Sorry – ours was yellow.

7. January 14, 2005 Electrostatics 7 Another Experiment ?? ------------------- Charged Rod Initially Neutral Metal Sphere

8. January 14, 2005 Electrostatics 8 Types of Materials Insulators  negative charges can move only with great difficulty Metal  negative charges move quite easily. Semiconductor  Ability for the negative charge to move depends on the impurities in the material as well as the temperature. Semi-Metals  Don’t ask!

9. January 14, 2005 Electrostatics 9 What is this “charge” thing? There are two charged particles we will be concerned with:  Electrons  Protons Electrons have a charge of –e Protons have a charge of +e ALL charges are an integral multiple of this fundamental charge “e”

10. January 14, 2005 Electrostatics 10 The Atom LIGHT

11. January 14, 2005 Electrostatics 11 What is e?? |e|=1.6 x 10 -19 Coulombs Exact value in textbook

12. January 14, 2005 Electrostatics 12 How Do We Know??? Millikan Oil Drop Experiment A Critical Balance

13. January 14, 2005 Electrostatics 13 The Electroscope & Induction Again

14. January 14, 2005 Electrostatics 14

15. January 14, 2005 Electrostatics 15 electrons

16. January 14, 2005Electrostatics16 Let’s Work a Few Problems if we have time.

17. January 14, 2005 Electrostatics 17 In the figure, particle 1 of charge +1.0 µC and particle 2 of charge -4.0 µC, are held at separation L = 11.0 cm on an x axis. If particle 3 of unknown charge q 3 is to be located such that the net electrostatic force on it from particles 1 and 2 is zero, what must be the coordinates of particle 3? x=[-11] cm y=[0] cm

18. January 14, 2005 Electrostatics 18

19. January 14, 2005 Electrostatics 19 Let’s Try It!

20. January 14, 2005 Electrostatics 20 A mechanics problem from the past! 

21. January 14, 2005 Electrostatics 21 Free Body Forces?

22. January 14, 2005 Electrostatics 22

23. January 14, 2005 Electrostatics 23 Find force on lower left particle.