The direction of this force must be OPPOSITE the E field because the electron carries a negative charge;
so, to the right .
Part 3—Potential
The nice thing about electric potential is that it is a scalar quantity, so we don’t have to concern ourselves
with vector components and other such headaches.
The potential at point P is just the sum of these two quantities. V = zero!
Notice that when finding the electric potential due to point charges, you must include negative signs ...
negative potentials can cancel out positive potentials, as in this example.
Gauss’s Law
A more thorough understanding of electric fields comes from Gauss’s law. But before looking at Gauss’s
law itself, it is necessary to understand the concept of electric flux.
Electric flux: The amount of electric field that penetrates an areaΦ (^) E = E · A
The electric flux, Φ (^) E , equals the electric field multiplied by the surface area through which the field
penetrates.
Flux only exists if the electric field lines penetrate straight through a surface. (Or, if the electric field
lines have a component that’s perpendicular to a surface.) If an electric field exists parallel to a surface,
there is zero flux through that surface. One way to think about this is to imagine that electric field lines are
like arrows, and the surface you’re considering is like an archer’s bull’s-eye. There would be flux if the
arrows hit the target; but if the archer is standing at a right angle to the target (so that his arrows zoom
right on past the target without even nicking it) there’s no flux.
In words, Gauss’s law states that the net electric flux through a closed surface is equal to the charge
enclosed divided by ε 0 . This is often written as
How and When to Use Gauss’s Law
Gauss’s law is valid the universe over. However, in most cases Gauss’s law is not in any way useful—no