1. Chapter 25 Capacitance-II In the last lecture: we calculated the capacitance C of a system of two isolated conductors. We also calculated the capacitance for some simple geometries. In this chapter we will cover the following topics: -Methods of connecting capacitors (in series, in parallel). -Equivalent capacitance. -Energy stored in a capacitor. -Behavior of an insulator (a.k.a. dielectric) when placed in the electric field created in the space between the plates of a capacitor. -Gauss’ law in the presence of dielectrics. (25 - 1)

2. HITT A. the work done by the field is positive and the potential energy of the electron-field system increases B. the work done by the field is negative and the potential energy of the electron-field system increases C. the work done by the field is positive and the potential energy of the electron-field system decreases D. the work done by the field is negative and the potential energy of the electron-field system decreases E. the work done by the field is positive and the potential energy of the electron-field system does not change An electron moves from point i to point f, in the direction of a uniform electric field. During this displacement: i j

3. (25 - 9)

4. (25 - 10)

5. (25 - 11)

6. (25 - 12)

16. A question What is the equivalent capacitance between the points A and B? A.1 μF B. 2 μF C.4 μF D.10μF E.None of these AB What would a 10V battery do, i.e. how much charge will it provide, when it is connected across A and B? 40 μC

17. - - - - - + + + + + dq' q'q'-q' V' q'q' q V Charge Voltage O A B (25 - 13)

18. - - - - - + + + + + q-q d AA (25 - 14)

19. q-q q'q' q q -q' -q V V V V'V' (25 - 15)

20. q -q q'q' q q -q' -q V V V V'V' (25 - 16)

21. conductordielectric q (25 - 17)

22. (25 - 18)

23. (25 - 19)

24. S S (25 - 20)

25. (25 - 21)

26. HITT A parallel-plate capacitor has a plate area of 0.2m 2 and a plate separation of 0.1 mm. To obtain an electric field of 2.0 x 10 6 V/m between the plates, the magnitude of the charge on each plate should be: A. 8.9 x 10 -7 CB. 1.8 x 10 -6 C C. 3.5 x 10 -6 CD. 7.1 x 10 -6 C E. 1.4 x 10 -5 C

27. A question Each of the four capacitors shown is 500 μ F. The voltmeter reads 1000V. The magnitude of the charge, in coulombs, on each capacitor plate is: A. 0.2B. 0.5C. 20D. 50E. none of these

28. Question A parallel-plate capacitor has a plate area of 0.3m 2 and a plate separation of 0.1mm. If the charge on each plate has a magnitude of 5x10 -6 C then the force exerted by one plate on the other has a magnitude of about: A. 0B. 5NC. 9ND. 1 x10 4 N E. 9 x 10 5 N

29. Question A parallel-plate capacitor has a plate area of 0.3m 2 and a plate separation of 0.1mm. If the charge on each plate has a magnitude of 5x10 -6 C then the force exerted by one plate on the other has a magnitude of about: A.0 B.5N C.0. 9N D.1 x10 4 N E.9 x 10 5 N The electric field = σ/2ε o why?