Electric Potential V
INTRODUCTION
Coulomb’s Law
Gauss’ Law
There is only one fundamental law on electricity --- either
Coulomb’s law or Gauss’ law. The other three fundamental
laws of E&M are either about magnetism or about interplays
between electricity and magnetism.
Why a new, “non-fundamental” quantity V?
E i.e., F
V i.e., U (energy)
1. Allows direct calculation of energy and power.
2. Often, calculating V first and then E is easier than directly
calculating E.
3. Very useful in understanding and designing electric circuits.
PLAN
1. Definition of V in terms of U.
2. Calculating V from E.
3. Electric potential V due to a point charge
and a group of point charges.
Definition of V in terms of U
A system of charged particles
q
3q
2q
Initial state
Final state
Q1: Which state has a higher electric potential
energy U?
Q2: Is the work done by “you” positive or
negative?
Q3: Is the work done by the electrostatic force F
(or the electric field E) positive or negative?