HVAC Star Practice Exam

Electrical potential difference is a measure of energy available per unit charge to move charges through a circuit. The unit that expresses energy per charge is the volt, defined as one joule per coulomb. That’s why potential difference is measured in volts.

Current is the rate at which charge flows (unit ampere), resistance is the opposition to current (unit ohm), and power is the rate of energy transfer (unit watt). The relationship V = I × R links voltage to current and resistance, reinforcing why volts are used for potential difference. For example, moving 1 coulomb of charge through a 1-volt difference involves 1 joule of energy, i.e., 1 volt.