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Welcome Back. Exam returned Wed or Friday. Problem 1 – We did it in class Problem 2 - A Web Assign Problem Problem 3 - Superposition Quiz on Friday (Capacitors) New WebAssign Posted … Wait until Wednesday to try. Chapter 25. Capacitors. Battery. Remember distributed Charges.

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Welcome Back

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  1. Welcome Back • Exam returned Wed or Friday. • Problem 1 – We did it in class • Problem 2 - A Web Assign Problem • Problem 3 - Superposition • Quiz on Friday (Capacitors) • New WebAssign Posted … Wait until Wednesday to try. Capacitors

  2. Chapter 25 • Capacitors Battery Capacitors

  3. Remember distributed Charges Capacitors

  4. Infinite Metal Plates + +++++++ - - - - - - - Capacitors

  5. Addemup + +++++++ - - - - - - - E=0 E=0 Capacitors

  6. Not quite infinite … Capacitors

  7. Capacitor • Composed of two metal plates. • Each plate is charged • one positive • one negative • Stores Charge • Can store a LOT of charge and can be dangerous! Capacitors

  8. A Simple Electric Circuit ? Capacitors

  9. Don’t ask questions because I don’t know the answers! Zn Metal Cu Metal Aqueous Solution of Capacitors

  10. What’s Next? • Zn(solid) Zn2+ +2e- • Electrons Hang Around • Zn ion goes into the solution. • Cu2+(solution) +2e-Cu depositing on Cu electrode Capacitors

  11. Capacitors

  12. For Additional Information Consult your Friendly Neighborhood Chemistry Professor! Capacitors

  13. Demo Capacitors

  14. d Air or Vacuum E - Q +Q Gaussian Surface Area A V=Potential Difference Gauss on Capacitors Same result from other plate! Capacitors

  15. d Air or Vacuum E - Q +Q Symbol Area A V=Potential Difference Two Charged Plates(Neglect Fringing Fields) Capacitors

  16. d Air or Vacuum E - Q +Q + Area A V=Potential Difference Note Consider a +q charge at the (-) plate. Move it to the (+) plate Work to do this is W=Fd=qEd also W=q(Vf-Vi)=qV Therefore Ed=V E=V/d E=V/d Capacitors

  17. Device • The Potential Difference is APPLIED by a battery or a circuit. • The charge q on the capacitor is found to be proportional to the applied voltage. • The proportionality constant is C and is referred to as the CAPACITANCE of the device. DEFINITION Capacitors

  18. UNITS Capacitors

  19. Look again Capacitors

  20. Continuing… • The capacitance of a parallel plate capacitor depends only on the Area and separation between the plates. • C is dependent only on the geometry of the device! Capacitors

  21. Diversion on Capacitors

  22. Two Metal Plates a Capacitor Make. Capacitors

  23. More is better! Capacitors

  24. Implementation - Variable Capacitors

  25. How do you do that? Capacitors

  26. Roll it up, Scottie Capacitors

  27. Stacked Disks, etc. Capacitors

  28. Units of e0 pico Capacitors

  29. Simple Capacitor Circuits • Batteries • Apply potential differences • Capacitors • Wires • Wires are METALS. • Continuous strands of wire are all at the same potential. • Separate strands of wire connected to circuit elements may be at DIFFERENT potentials. Capacitors

  30. Size Matters! • A Random Access Memory stores information on small capacitors which are either charged (bit=1) or uncharged (bit=0). • Voltage across one of these capacitors ie either zero or the power source voltage (5.3 volts in this example). • Typical capacitance is 55 fF (femto=10-15) • Question: How many electrons are stored on one of these capacitors in the +1 state? Capacitors

  31. Small is better in the IC world! Capacitors

  32. TWO Types of Connections SERIES PARALLEL Capacitors

  33. V V CEquivalent=CE Parallel Connection C1 C2 C3 Capacitors

  34. q -q q -q V C1 C2 Series Connection The charge on each capacitor is the same ! Capacitors

  35. V1 V2 q -q q -q C1 C2 V Series Connection Continued Capacitors

  36. For Bunches of Capacitors Capacitors

  37. Capacitors

  38. Example C1=12.0 uf C2= 5.3 uf C3= 4.5 ud C1 C2 series (12+5.3)pf V C3 Capacitors

  39. E=e0A/d +dq +q -q More on the Big C • We move a charge dq from the (-) plate to the (+) one. • The (-) plate becomes more (-) • The (+) plate becomes more (+). • dW=Fd=dq x E x d Capacitors

  40. So…. Capacitors

  41. Parallel Plate Cylindrical Spherical Not All Capacitors are Created Equal Capacitors

  42. Spherical Capacitor Capacitors

  43. Calculate Potential Difference V (-) sign because E and ds are in OPPOSITE directions. Capacitors

  44. Continuing… Lost (-) sign due to switch of limits. Capacitors

  45. Real Materials • Consist of atoms or molecules bonded together. • Some atoms and molecules do not have dipole moments when isolated. • Some do. • Two types to consider: • Polar • Non-Polar Capacitors

  46. Polar Molecule E Capacitors

  47. Polar Materials Capacitors

  48. Capacitors

  49. Apply an Electric Field Some LOCAL ordering Large Scale Ordering Capacitors

  50. Adding things up.. - E + Net effect REDUCES the field Capacitors

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