voltage drop

Meaning: Voltage drop is the potential difference between the two ends of a component. It is the electrical energy per unit charge converted to other forms, usually heat in a resistor. Potential falls in the direction of conventional current through a resistor. Kirchhoff's loop rule says the potential changes around a closed loop sum to zero, so the drops across the elements balance the emf of the source. In series, the current is the same through each resistor, so the larger resistance gets the larger drop. In parallel, each branch has the same voltage drop and the current divides among them.

Equation: V = IR, where V is the voltage drop across the resistor (volts, V), I is the current through it (amperes, A), and R is its resistance (ohms, Ω).

On the MCAT: A passage gives a battery and several resistors. You find the equivalent resistance, get the current from I = emf/Req, then find the drop across one resistor. Questions also ask how a drop changes when a resistor is added or removed, or which bulb is brightest, using P = IV. Ideal wires are treated as having negligible drop.

Common confusion: Students say current is used up in a resistor. In a series path the current is the same entering and leaving, and what falls is the potential, meaning energy per charge. Parallel resistors do not split the voltage. They share the same drop, and the current divides.