1. Today 2/24  Read 18.6 about E-Fields note we put E-field first and Force second  E-Field Lines Chapter 18.7 Today  Lab: “Electrostatics” Read 18.4 in text for background  HW:None assigned

2. Electrostatics Lab: This should be Fun! Tools: electroscope “proof plane” metal cup ground wire charging rod and glass delicate gold foil proof plane

3. Proof Plane: What happens… (Start with the proof plane uncharged)...when the metal touches a charged insulator? proof plane...when the metal touches an uncharged plate?...when the metal touches a charged plate? some rubs off nothing charge moves through the conductors …when the metal touches the center of the plate???

4. Two identical positive charges, A and B, are arranged as shown. The distance from point C to A is twice the distance from point C to B. Which of the following best represents the electric field at point C? e d c b a A BC

5. e d c b a A BC

6. Field Lines If we want to draw a picture of the E-Field everywhere at once we must fill space with X’s and arrows.

7. Pepe le Pew:

8. Where is Pepe?

10. The closer we get to the source, the closer together the lines of STINK and the bigger the PU. PU!

11. What if it’s a HOT DAY? More STINK means more lines.

12. Field Lines If we want to draw a picture of the E-Field everywhere at once we must fill space with X’s and arrows. Red “E-Field lines” display the information more clearly.

13. Field Lines If we want to draw a picture of the E-Field everywhere at once we must fill space with X’s and arrows. Red “E-Field lines” display the information more clearly.

14. Electric Field Lines:  direction of E-field vector at any point is parallel to the lines near that point  magnitude of E-field vector at any point is proportional to line density (line spacing)  number of lines leaving or entering a charge is proportional to the size of the charge (more charge, more lines)  away from positive charge and toward negative charge

15. What direction would the force point on a small positive charge at 1,2,3? Compare the size of the force exerted on a small charge at a. 1 and 2 b. 2 and 3 The test charge is doubled when at 2 a. how does the force change? b. how does the electric field change?

16. What direction would the force point on a small positive charge at 1,2,3? Compare the size of the force exerted on a small charge at a. 1 and 2 b. 2 and 3 The test charge is doubled when at 2 a. how does the force change? b. how does the electric field change? 1 larger

17. What direction would the force point on a small positive charge at 1,2,3? Compare the size of the force exerted on a small charge at a. 1 and 2 b. 2 and 3 The test charge is doubled when at 2 a. how does the force change? b. how does the electric field change? 2x Stays the same 3 larger 1 larger