4.1 Electric Fields

Fields

  • a region in which an object may experience a force
    • electric field, charged objects experience a force

Electric fields

  • produced by objects with a charge
  • represented by field lines that show the direction of a positively charged particle
  • charge is a property - like mass, temperature or speed
  • even if there are no charged objects around, the field is still there, it’s just 0
  • the denser the lines (the closer the lines are), the stronger the field
    • in diagrams with multiple objects, objects with more charge are drawn with more field lines
  • always drawn perpendicular (90°) to the surface of a charged particle or object
  • never cross - show the direction of the net force, not the individual forces from each charged object
  • to determine ratio, look at the density of the lines from the object
  • electric fields curve because it wants to go away, but is attracted to the negative

Types of charged objects

  • point charges
    • very small charged objects that don’t have a distributed mass
    • assume entire charge is located at one point in space
      • good models for protons, electrons
    • represented by circles
  • unit charge - unit means 1, so has a charge of 1 (positive or negative)
  • parallel charged plates
  • parallel charged plates and a point charge

Coulomb’s Law

  • inverse square law

    permittivity of free space - measure of how difficult it is to form an electric field

  • don’t get confused by this though - the law still works outside of a vacuum, net force may change for other reasons

  • can be rearranged to:

    • F/q = 1/constant = q/r^2