Which quantity requires using the sign of the charge when calculating energy from a potential?

• A. Electric potential energy
• B. Electric potential
• C. Electric field
• D. Voltage

Answer: (A)

Energy from a potential is found by multiplying the potential by the charge: U = qV. The sign of the charge matters because it sets the sign of the energy. A positive charge in a positive potential has positive energy, while a negative charge in the same potential yields negative energy. Since energy depends on both the potential and the charge, you must include the sign of the charge to get the correct energy value. The quantity that this relation describes is electric potential energy—the energy a specific charge has due to its location in the electric potential. The electric potential itself is energy per unit charge, and the electric field relates to the potential by E = -∇V; voltage is just the potential difference, which sets the scale for energy once the charge sign is known.