Which equation correctly expresses voltage as a function of power and current?

• A. V = P * I
• B. V = I / P
• C. V = P / I
• D. V = R * I

Answer: (C)

Power in a circuit equals voltage times current, P = V × I. To get voltage when you know power and current, rearrange that equation to solve for V: V = P / I. This matches the definitions and units—if you multiply voltage by current you get power, so dividing the known power by the known current yields the voltage.

The other forms don’t fit this scenario. V = P × I would mix power and current to an incorrect quantity with mismatched units, not volts. V = I / P has incorrect units for voltage. V = R × I is Ohm’s law, which expresses voltage in terms of resistance and current, not power. For example, if P is 60 W and I is 2 A, V = P / I = 30 V, and P = V × I = 60 W checks out.