electric potential
Summary
Electric potential is the electric potential energy per unit charge at a point, V = U/q, measured in volts (J/C). For a point charge V = kQ/r, a scalar that adds algebraically. A positive charge released from rest moves toward lower potential, a negative charge toward higher.
Detail
Meaning: Electric potential at a point is the potential energy per unit positive charge placed there. It is set by the source charges, not by the test charge. Only differences matter: a positive charge released from rest moves toward lower potential, a negative charge toward higher. Potential is a scalar, so contributions from several point charges add algebraically with sign. Equipotential lines are perpendicular to field lines, and moving a charge along one takes no work.
Equation: V = U/q = kQ/r, and ΔV = −Ed in a uniform field. V is potential (V = J/C), U is potential energy (J), q is test charge (C), k = 9.0 × 10⁹ N·m²/C², Q is source charge (C), r is distance (m), E is field strength (V/m or N/C), d is displacement along the field (m).
On the MCAT: Expect summing kQ/r for several charges, predicting which way a charge moves, or finding kinetic energy gained across a potential difference (KE = qΔV). Parallel-plate and equipotential diagrams also appear; closer spacing of equipotentials means a stronger field.
Common confusion: Potential is not potential energy. U = qV, so the sign of q matters. Zero potential does not mean zero field: midway between equal and opposite charges V = 0 but E ≠ 0.
Sources
- Physics (Giancoli)
- Fundamentals of Physics (Halliday, Resnick, Walker)
- University Physics (Young and Freedman)
Written for the MCAT and checked before it was published. For study reference only. Spotted an error? Let us know.