For instance consider the map of the Rawah Wilderness on the right. All points on the same line are at the same elevation, just as all points on the same equipotential lines are at the same voltage. Water will always flow downhill,hence the rivers are always perpendicular to the lines on the topographic map, similar to the way electric field lines are always perpendicular to equipotential lines. When lines are close together, the slope is steep, e.g. a cliff, just as close equipotential lines indicate a strong electric field. Lakes are at the same elevation, in the same way conductors are at the same potential. |
|
 The figure to the left
shows equipotential lines. The electric field at
point a can be found by calculating the
slope at a:
where
|
is the voltage difference
between the two lines near a, and 
is the distance between the two lines
nearest a.Rules for equipotential lines:
- Electric field lines are perpendicular to the equipotential lines, and point "downhill".
- A conductor forms an equipotential surface.
- When lines are close to each other, the electric field is strong.