Electric potential energy per charge unit is called what?

• A. Current
• B. Resistance
• C. Power
• D. Voltage

Answer: (D)

Voltage is the electric potential energy per unit charge. Every charge placed in an electric field has potential energy U = qV, where q is the charge and V is the electric potential difference between two points. The unit of V is the volt, defined as one joule per coulomb, so a unit positive charge would have energy equal to V joules when moved across that potential difference. This is why voltage is described as energy per charge, while current is the flow of charge, resistance is how much a material opposes that flow, and power is the rate at which energy is transferred (P = VI). For example, moving a 3 C charge through a 2 V potential difference changes its energy by ΔU = qΔV = 3 × 2 = 6 joules.