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Understanding Electric Fields: Concepts, Equations, and Calculations

Learn about electric fields, forces, potential, capacitance with equations and calculations. Understand field lines, equipotential, grounding, and more.

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Understanding Electric Fields: Concepts, Equations, and Calculations

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  1. Chapter 21 Electric Fields

  2. 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.

  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’ = q’E

  7. Calculate the electric field strength when a 25 N force at 37o NoE 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 req 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 in 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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