-Electric Potential Energy and Electric Potential due to Point Charges AP Physics C Mrs. Coyle

Electric Potential Due to a Point Charge V abs = k Q / r

Electric Potential due to a Point Charge The absolute potential of any position in its electric field is:V abs = k Q / r. When the charge Q creating the field is positive, the potential is positive; when the central charge Q is negative, the potential is negative. As r  ∞, the absolute potential is defined to be zero.

Potential Difference due to a Point Charge

The electric potential is independent of the path between points A and B It is customary to choose a reference potential of V = 0 at r A = ∞ Then the potential at some point r is

Electric Potential vs Distance from a Positive Point Charge The red line shows the 1/r nature of the potential. If the central point charge is negative, V is negative and the graph is a hole.

Electric Potential with Multiple Charges The electric potential due to several point charges is the sum of the potentials due to each individual charge  This is an example of the superposition principle  The sum is the algebraic sum  V = 0 at r = ∞

Equipotential Lines Simulation of Field with Equipotential Lines hill.com/sites/ /student_view0/chapter21/elec tric_fields_applet.htmlglencoe.mcgraw- hill.com/sites/ /student_view0/chapter21/elec tric_fields_applet.html

Graphs of V and E vs r for a point charge E decreases more sharply

Problem 1 If the central charge was +10 mC, what is the potential at surface A where r A = 3 meters and at surface B where r B = 1 meter? Ans: 3X10**7 V, 9X10**7 V

Problem 2 Calculate the Potential and the Electric Field at the midpoint. What does this graph represent? Ans: -Net E = 2kq/r 2 towards the right -Net V = 0

Problem Find E and V at center of square in terms of q, r.