1. HW1 return! FERPA-approved military fashion!

2. Equipotential and field lines: Equipotential lines field lines:

4. Equipotential lines and the Electric field: Quantitative relation

5. ? Equipotential lines and the Electric field: Quantitative relation

6. Equipotential lines and the Electric field: Quantitative relation

7. Small enough scale, looks like parallel plate field: In direction of

8. Small enough scale, looks like parallel plate field: (calculate) In direction of

9. Formally: Direction: downhill

10. Pretending that V(x) is like a topographic map: A)The Electric field always points in the direction of steepest descent! B) The magnitude of the electric field is given by the slope in that direction! alternate units for E : V/m

11. Estimating Electric field strength:

12. Something Unrelated ….

13. Example 17.22 where’s V = 0? 5 cm Two possibilities!

14. Example 17.22 where’s V = 0? 5 cm x Possibility #1

15. Example 17.22 where’s V = 0? x Possibility #2

16. Conductors!

21. Electric fields just outside of a conductor are strong where the conductor is pointy: Dielectric strength of a material = maximum electric field the Material can stand before breaking down. Dielectric strength of air = 3 × 10 6 V/m Example: Voltage of a 15 cm spark!

22. Capacitance:

23. Must be at different potentials!

24. Capacitance:

26. Parallel-plate capacitor: 10 cm 0.1 cm Square plates 10 cm

27. Parallel-plate capacitor: Q = ?

28. Parallel-plate capacitor: Dielectric constant! 0.1 cm 10 cm Dielectric! Square plates Quartz:  = 4.3

29. Leyden-jar demo V de G demo again, big and little spheres – spark size