How is energy transferred in a circuit calculated?

• A. Energy transferred = charge × voltage.
• B. Energy transferred = voltage × resistance.
• C. Energy transferred = current × resistance.
• D. Energy transferred = charge ÷ voltage.

Answer: (A)

Energy transferred in a circuit comes from doing work on charges as they move through a potential difference. The amount of energy transferred is the charge moved times the potential difference it experiences, so E = Q × V. Each coulomb of charge moving across a voltage V gains V joules of energy, giving the total energy as QV. You can also see this as E = VIt, since current I = Q/t, which makes E = V × I × t = QV, a consistent result. The other forms don’t give energy in joules: voltage times resistance has the wrong units, current times resistance also has the wrong units, and charge divided by voltage gives capacitance, not energy.