potential difference

Meaning: Potential difference (voltage) is the change in electric potential energy per unit charge between two points. A positive charge released from rest moves toward lower potential; a negative charge moves toward higher potential. A battery maintains a potential difference that drives current.

Equation: ΔV = ΔU/q, where ΔV is the potential difference (volts, V = J/C), ΔU is the change in electric potential energy (J), and q is the charge moved (C).

On the MCAT: Expect a charge accelerated through a potential difference, gaining kinetic energy qΔV, or a parallel-plate setup with ΔV = Ed (E is field strength in V/m, d is separation in m). In circuits, V = IR (current times resistance), parallel branches share the same ΔV, series resistors split it, and potential changes sum to zero around a loop. Equipotential lines are perpendicular to field lines, so no work is done moving a charge along one.

Common confusion: Potential difference is not potential energy: ΔU = qΔV depends on the charge, but ΔV does not. Potential at a single point needs a chosen zero, such as ground, so only differences matter. Electrons move toward higher potential, so "high to low" describes positive charges only.