Electric fields

• An electric field is a region of space where a charged particle will experience a force
• Charging by friction


  An object has electrons added or removed from it by friction
• Charging by contact


  A charged rod is touched on the surface of the object and some of its charge is transferred
• Charging by induction


  A charged rod is brought close to the object and then the object is earthed and the rod is removed
• Electrical conductor


  Charges are free to move
• Electrical insulator


  Charges are not free to move
• Gold leaf electroscope 


  This is an instrument for detecting and measuring static electricity or voltage
• Van de Graaff generator

  This machine uses static electricity to produce very high voltages
• Forces between two charged particles - Coulombs law

  F = k( Q1Q2/ r^2)
• Electric field lines


  Electric field lines represent the field around a charged object
• Distance between field lines represents the strength of the field, the closer they are the stronger the field
• The direction of the field lines is shown by an arrow from positive to negative - the direction a small positive test charge would move
• Field lines will never

  • Start or stop in empty space - they start/stop on a charge or at infinity
  • They will never cross
• Equipotentials are perpendicular to the field lines
• Electric field strength equation

  E = F / Q
• Electric field strength in a uniform field equation

  E = V/D