electrical potential

Meaning: Electric potential at a point is the potential energy a unit positive test charge would have there. It is set by the source charges and exists whether or not a test charge is present. By convention V = 0 at infinity, so a positive source gives positive potential nearby and a negative source gives negative potential. A positive charge released in a field moves toward lower potential, and a negative charge moves toward higher potential. Potential is a scalar, so potentials from several charges add as ordinary numbers.

Equation: V = U/q = kQ/r, where V is electric potential (volts, V = J/C), U is electric potential energy (J), q is the test charge (C), k is Coulomb's constant (about 9.0 × 10⁹ N·m²/C²), Q is the source point charge (C), and r is the distance from it (m).

On the MCAT: Expect a point-charge or parallel-plate setup. You may be asked to sum potentials from two charges, find the work to move a charge (W = qΔV), or compare equipotential lines, which are always perpendicular to field lines. In a uniform field, E = |ΔV|/d, in V/m. The field points toward decreasing potential.

Common confusion: Potential (V, in J/C) is not potential energy (U, in J); U = qV, so the sign of q matters for U but not for V. Also, zero field does not mean zero potential. At the midpoint of two equal like charges E = 0 but V is not zero. At the midpoint of a dipole V = 0 but E is not zero.