Final answer:
An equipotential surface is the equipotential surface of Earth's gravity field that most closely approximates the mean sea surface.
They are always perpendicular to electric field lines and can be represented by equipotential lines in two-dimensional space or a three-dimensional surface.
Step-by-step explanation:
An equipotential surface is the equipotential surface of Earth's gravity field that most closely approximates the mean sea surface.
Equipotential surfaces are the collection of points in space that are all at the same potential.
They are always perpendicular to electric field lines and can be represented by equipotential lines in two-dimensional space or a three-dimensional surface.