Monthly Archives: March 2018

Parallel Plate Capacitor Electric Fields

The purpose of the parallel plate capacitor simulation is to let the user explore the almost uniform electric and potential fields in a parallel plate geometry.  A complete worksheet is available to guide students in this exploration.  Note the following: 

  • The fields are very uniform in between the plates
  • The number of E-lines is proportional to the charge in Coulombs (C)  
  • The E-field strength is proportional to the density of the E-lines
  • The voltage gradient is proportional to the E-field strength
  • Very low density E-field extends outside the parallel plates, called the “fringing field” 
  • The “fringing field” located at the capacitor ends is non-uniform

In order access the capacitor simulation website, use the following information:

Student Worksheet Downloadable Word Doc

We used the following word document as a lab procedure in the PHY112 class.  However, it can be used possibly in PHY101 as well, because questions are qualitative.


Points for Discussion
  • The electric field is a force field: The force on a positive charge has direction parallel to the electric field lines. The magnitude of force is proportional to the density of the E-field lines.
  • All electric field lines start on the positive plate and terminate on the negative plate.
  • The “fringing field” is a weak E-field found at the open ends of the capacitor.  The field is weak and gets weaker the farther one gets from the charged plates.  However, if you study the fields at the highest level of charge, and at the very corner of the metal plates, you will see that the E-field is especially large right there.  This is due to an accumulation of charge at the corners of the plates.