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For more information, please see full course syllabus of AP Physics B
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Electric Field

  • Electric charges produce an electric field that fills the space. To find the value of the electric field E at a point, we place a very small point charge q at that point and measure the force F acting on the point charge; the electric field is then given by E = F / q. Note that the electric field is a vector, since F is a vector.
  • The electric field produced by a point charge Q at a distance r has a magnitude E = kQ/r^2. The field is directed radially outward if Q is positive and radially inward if Q is negative.
  • The electric field produced by a collection of point charges is equal to the vector sum of the fields produced by the individual point charges.
  • Between the plates of a charged parallel-plate capacitor, E = σ / ε0, where σ is the surface charge density on the plates and ε0 is the permittivity of free space.
  • Electric field lines are always tangent to the electric field at every point in space. The lines always begin at positive charge and end on negative charge, and their density is proportional to the field strength.
  • Under electrostatic conditions, any excess charge, added to a conductor, must reside on the conductor surface.

Electric Field

Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.

  • Intro 0:00
  • Definition of Electric Field 0:11
    • Q1 Produces Electric Field
    • Charges on a Conductor
  • Field of a Point Charge 13:10
    • Charge Point Between Two Fields
    • Electric Field E=kq/r2
    • Direction of the Charge Field
    • Positive Charge, Field is Radially Out
  • Field of a Collection of a Point Charge 19:40
    • Two Charges Q1,Q2
    • Q1 Positive, Electric Field is Radially Out
    • Q2 is Negative, Electric Field is Radially Inward
    • 4 Charges are Equal
  • Parallel Plate Capacitor 25:42
    • Two Plates ,Separated by a Distance
    • Fringe Effect
    • E=Constant Between the Parallel Plate Capacitor
  • Electric Field Lines 35:16
    • Pictorial Representation of Electric Field
    • Electric Lines are Tangent to the Vector
    • Lines Start at Positive Charge, End on Negative Charge
    • Parallel Line Proportional to Charge
    • Lines Never Cross
  • Conductors and Shielding 49:33
    • Static Equilibrium
    • No Net Moment of Charge
    • Electric Field is Perpendicular to the Surface of Conductor
  • Extra Example 1: Plastic Sphere Between Capacitor
  • Extra Example 2: Electron Between Capacitor
  • Extra Example 3: Zero Electric Field
  • Extra Example 4: Dimensional Analysis