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Chapter 21

An electric force of 4.5 x 10 -5 N is measured between two particles. One particle has a charge of 2.0 x 10 -6 C & the other has a charge of 3.0 x 10 -8 C. Calculate the distance between them. Chapter 21. Electric Fields.

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Chapter 21

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  1. An electric force of4.5 x 10-5 N is measured between two particles. One particle has a charge of2.0 x 10-6 C & the other has a charge of 3.0 x 10-8 C. Calculate the distance between them.

  2. Chapter 21 Electric Fields

  3. Electric force like gravitational force is inversely proportioned to the square of the distance between the two points of concern

  4. Electric Field (E) • A vector quantity that relates the force exerted on a charge to the amount of the charge

  5. Electric Field (E) Fon q q E =

  6. Electric Field (E) Fon q = qE

  7. Calculate the electric field strength when a 25 N force is exerted on a charge of + 5.0 x 10-6 C

  8. Typical Field Strengths Field Value (N/C) TV tube 1 x 105 Spark r 3 x 106 H orbital 5 x 1011

  9. Electric Field Lines • Lines representing the force vectors in an electric field

  10. Electric Field Lines +

  11. Electric Field Lines -

  12. Electric Field Lines - +

  13. Electric Field Lines • Always point from positive to negative

  14. Electric Field Lines • Do not exist , but provide a model of a field

  15. The electric field between two parallel plates is uniform

  16. + -

  17. Electric Potential • The electric potential difference of charges measured in volts

  18. Electric Potential • As with heat, we can only measure potential difference (DV)

  19. Electric Potential Difference (DV) • The change in potential energy per unit charge

  20. Electric Potential Difference (DV) • The work done moving a charge thru a field charge

  21. Electric Potential Difference (DV) • Measured in J/C • J/C = volt (V)

  22. Electric Potential Difference (DV) W on q q DV =

  23. Electric Potential Difference (DV) DU = W

  24. Electric Potential Difference (DV) DUq q DV =

  25. Electric Potential Difference (DV) W on q q DV =

  26. Electric Potential Difference (DV) W = Fd

  27. Electric Potential Difference (DV) Fd on q q DV =

  28. Electric Potential Difference (DV) F q DV = x d

  29. Electric Potential Difference (DV) F q E =

  30. Electric Potential Difference (DV) DV = Ed

  31. Basic Equations • V = Ed • W = qV • F = qE

  32. Equipotential • When the electric potential difference is 0

  33. Equipotential • Charge rearranges itself to reach equipotential

  34. Equipotential • When two spheres have the same charge, the larger one has lower electric potential

  35. Equipotential • When two spheres have the same electric potential, the larger one has the greater charge

  36. Equipotential • When a charged object comes in contact with a neutral one, the charge is • equally distributed

  37. Equipotential • Because of the size of Earth, when objects touch Earth, their charge is passed to the Earth

  38. Grounding • When a charged object touches Earth, all its charge flows to Earth creating equipotential

  39. Electric Fields • All charges are on the outside of a conductor

  40. Electric Fields • In pointed object, the field strength is greatest at the point

  41. Capacitor • A device designed to store a charge

  42. Capacitance • The ratio of charge to electric potential difference

  43. Capacitance (C) q DV C =

  44. Farad (F) • Unit for capacitance measured in coulombs per volt: F = C/V

  45. Basic Equations • V = Ed • W = qV • F = qE • q = CV

  46. A charge of 1.6 x 10-6 C is stored to create a capacitance of 4.0 x 10-3 F acting over 2.0 mm. Calculate: V, E, F, & W

  47. A charge of 1.5 x 10-6 C is stored to create a capacitance of 4.0 x 10-3 F acting over 2.0 mm. Calculate: V, E, F, & W

  48. A charge of 3.2 x 10-4 C is stored to create a capacitance of 8.0 mF acting over 4.0 mm. Calculate: V, E, F, & W

  49. Charge =1.6 x 10-6 C Force = 3.2 x 10-3 N Distance = 64 nm. Calculate: V, E, C, & W

  50. Calculate: 3.2 x 10-144x 1.5 x 10162 8.0 x 10-256 7.5 x 10175x 4.0 x 10122 =

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