Equipotential Surfaces and Capacitors

• All points on an equipotential surface have the same electric potential (i.e. the same voltage).
• The electric force neither helps nor hinders motion of an electric charge along an equipotential surface.
• Electric field lines are always perpendicular to an equipotential surface.
• Electric potential is analogous to altitude; one can make maps of each in very similar ways.
• The electric field strength can be determined by looking at the local spatial gradient of the electric potential:

                                change in potential
               electric field = --------------------
                                     distance
  

• A capacitor is a device which stores positive and negative charges in separate places.
• The capacitance of a device tells how much charge it can store for a given voltage across it:

                               charge            coulombs
               capacitance = -----------         -------- = farads
                               voltage             volts
  

• The energy stored in a capacitor is

  
               energy stored = 0.5 * (capacitance) * (voltage)^2
  

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Copyright © Michael Richmond. This work is licensed under a Creative Commons License.