1. Last Time Transient response when connecting a circuit How long until steady state is reached? Kirchhoff's Voltage Loop Law (Difference configuration of circuit). 1

2. Nichrome wire (resistive) Twice the Length Quantitative measurement of current with a compass Current is halved when increasing the length of the wire by a factor of 2. 2

3. Doubling the Cross-Sectional Area Nichrome wire If A doubles, the current doubles. 3

4. Today (Difference configuration of circuit). Charge and discharge capacitors Different way of connecting capacitors. (More details on resistance) 4

5. iClicker Questions When plug in two batteries instead of one, the current will be A.Double B.Halved C.unchanged 5

6. Why light bulb is brighter with two batteries? Work per second: Two Batteries in Series Two batteries in series can drive more current: Potential difference across two batteries in series is 2emf  doubles electric field everywhere in the circuit  doubles drift speed  doubles current. 6

7. How Do the Currents Know How to Divide? 7

8. Capacitor: Charging and Discharging ChargingDischarging

9. Similar to a large parallel plate capacitor s D Capacitor: Construction and Symbols There is no connecting path through a capacitor

10. Positive and negative charges are attracted to each other: how can they leave the plates? Fringe field is not zero! How is Discharging Possible? Electrons in the wire near the negative plate feel a force that moves them away from the negative plate. Electrons near the positive plate are attracted towards it.

11. E-E- E+E+ E net s z 0 Units:  Inside: Fringe: Step 4: check the results: Electric Field of a Capacitor 11 From Lecture 6

12. Capacitor: Discharge Electron Current Electric Field

13. Fringe field of a capacitor rises until E=0 in a wire – static equilibrium. Capacitor: Charging

14. Ultimately, the fringe field of the capacitor and the field due to charges on the wire are such that E=0 inside the wire. At this point, i=0. Why does current ultimately stop flowing in the circuit?

15. iClicker Question. Charging Which of the following is correct? A.The light bulb will glow all the time B.The light will not glow at all C.The light bulb will glow but will grow darker till completely off.

16. Demos: 6C-14 Charging and Discharging Capacitors

17. Thick filamentThin filament Which light bulb will glow longer? Why? 1)Round is brighter  capacitor gets charged more? 2)Long bulb glows longer  capacitor gets charged more? The Effect of Different Light Bulbs After current stops, Voltage across capacitor = Voltage across battery no matter which bulb is used. Capacitor charged by same amount in both cases.

18. Use two different capacitors in the same circuit In the first moment, which capacitor will cause the bulb to produce more light? Which capacitor will make the light bulb glow longer? Fringe field: IClicker Question: Effect of the Capacitor Disk Size A.Upper longer, lower brighter B.Upper longer, upper brighter C.Lower longer, lower brighter D.Lower longer, upper brighter

19. In the first moment, which capacitor will cause the bulb to produce more light? Fringe field: Which capacitor will make the light bulb glow longer? iClicker question: Effect of the Capacitor Disk Separation A.Upper longer, lower brighter B.Upper longer, upper brighter C.Lower longer, lower brighter D.Lower longer, upper brighter

20. In the first moment, which capacitor will cause the bulb to produce more light? Fringe field: Which capacitor will make the light bulb glow longer? Insulator Effect of Insulator in Capacitor A.Upper longer, lower brighter B.Upper longer, upper brighter C.Lower longer, lower brighter D.Lower longer, upper brighter

21. Initial moment: brighter? Will it glow longer? Parallel Capacitors Fringe field: Capacitors in parallel effectively increase A

22. Will it glow at all? How do electrons flow through the bulb? An Isolated Light Bulb A.Yes B.No because it’s an open circuit.

23. I 1 = I 2 + I 3 Charge conservation: I i > 0 for incoming I i < 0 for outgoing Capacitor transients: not a steady state! Cannot use Kirchhoff rule for a part of a capacitor (area 1 or 2) But can use for capacitor as a whole (area 3) The Current Node Rule in a Capacitor Circuit …in steady state