equipotential

Meaning: An equipotential is a line, surface, or region where every point has the same electric potential. A charge moved along it has no change in potential energy, so the field does no work. The electric field is therefore perpendicular to the equipotential and points toward lower potential. Examples: concentric spheres around a point charge, planes parallel to capacitor plates, and a conductor in electrostatic equilibrium.

Equation: W = qΔV = 0, where W is the work done by the field (J), q is the charge (C), and ΔV is the potential difference between the two points (V). In a uniform field, E = |ΔV|/d, where E is the field magnitude (V/m) and d is the separation of two equipotentials (m).

On the MCAT: Passages show equipotential lines around charges or between plates. You may be asked for field direction (perpendicular to the lines, toward lower V), to compare field strength (closer lines mean a stronger field), or to decide whether work is done moving a charge between two points. That work depends on the potentials at the endpoints, not the path.

Common confusion: Equipotential does not mean zero field, and it does not mean V = 0. The field can be strong, but it has no component along the surface. The constant value of V depends on the chosen reference point.