Physlet Illustration: Electric Charge and Potential Energy



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In this simulation, two parallel plates, located at y= +4 mm and  y= -4 mm are fixed at ± 4 Volts, respectively. The electric field lines between the plates are shown. A particle (m = 1 gm, q = +1 mC) is released from rest at a point near the top (positive) plate. Its velocity is shown in m/s. Can you verify that the total energy of the particle is conserved?


  1. The electric field between the plates is uniform. How, then, does the electric potential vary at different points between the plates?
  2. Pause the animation at some point. What is the particle's position? What is the electric potential at that position? What, then, is the particle's electric potential energy?
  3. How fast is the particle moving at this point? What is its kinetic energy ?
  4. What is the sum of kinetic and potential energies?
  5. Now, restart the animation and pause at a later time. Repeat your calculations. Is the total energy the same?


See Walker, Section 20-2

Illustration written by Steve Mellema