voltage

Meaning: Voltage, or potential difference ΔV, is the work per unit charge needed to move a charge between two points. A battery or other source does work on charges to maintain a voltage. A positive charge released in a field moves toward lower potential, and a negative charge moves toward higher potential. Voltage is a scalar and depends only on the two end points, not on the path.

Equation: ΔV = ΔU/q = IR = Ed. ΔV is potential difference (V), ΔU is change in electric potential energy (J), q is charge (C), I is current (A), R is resistance (Ω), E is uniform field magnitude (V/m), and d is separation along the field (m).

On the MCAT: Circuit passages ask you to apply Kirchhoff's loop rule. Voltage drops across series resistors add up to the source voltage, and parallel branches have the same voltage across each. For a capacitor, V = Q/C. Particle problems ask for the kinetic energy gained by a charge accelerated through a potential difference, KE = qΔV. Figures may show equipotential lines, where no work is done moving a charge along a line.

Common confusion: Voltage is measured across two points, not through a component; current is what flows through. Potential energy and potential are different quantities, linked by U = qV. Only differences in potential matter, because the zero point is a choice.