- Let Q = 2 × 10−9 C. What is the potential at a point P that is 2 cm
from Q?
Here’s How to Crack It
Relative to V = 0 at infinity, we have
Notice that, like potential energy, potential is a scalar. In the preceding example,
we didn’t have to specify the direction of the vector from the position of Q to the
point P because it didn’t matter. At any point on a sphere that’s 2 cm from Q, the
potential will be 900 V. These spheres around Q are called equipotential surfaces,
and they’re surfaces of constant potential. Their cross sections in any plane are
circles and are, therefore, perpendicular to the electric field lines. The
equipotentials are always perpendicular to the electric field lines.