AP: Things to study for electric potentials test next week

1) Fields and potentials from point charge arrays.  Know what to do with differing signs when finding field intensities and when finding the electric potential.  Know how to calculate the work done when moving a charge around.

2) Fields and potentials of continuous distributions of charge.  Option 1: If I give you a charge and a geometry (e.g., spherical) you tell me the function of the field and the electric potential with respect to space (r).  Option 2: I give you the potential, you tell me the charge and find me a function of the field.

  • Know your symmetries: Spherical, Cylindrical, Planar
  • When finding the potential, integrate from most negative (or zero) to most positive–>this is lowest potential to highest potential.
  • Know how to differentiate between conductors and insulators INSIDE
  • Recognize that OUTSIDE of a shape it doesn’t matter if the object is a conductor or insulator
  • Be able to graph your E vs. r and V vs. r functions.  Be able to identify critical values on both the x- and y-axes.

3) Field mapping: Know the relationship between the field and the potential on both a graph and on a field plot (like the lab).  Know how to find equipotential lines from field lines and vice-versa.  Know how to calculate work done when moving charge between equipotentials.  Know that NO WORK IS DONE when moving charge along an equipotential.  Know that if the field is uniform (all lines going the same direction with the same spacing) then you can treat it like a parallel plate capacitor (V=Ed).  Know that field lines point toward negative charge, or in the direction of decreasing potential.

4) Capacitors: Know the definition of capacitance.  Know how to derive the formula for the capacitance of a parallel plate capacitor.  Know the factors which vary the capacitance for a parallel plate capacitor.  Know what happens when a dielectric is put in a capacitor.  Know series and parallel wiring rules for capacitors.


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