Ohm's law and the power law describe the relationship between the following four electrical entities: Entity. Unit. Symbols. Voltage. Volts. V. Current. Amps. A, i. Resistance. Ohms. ω, r. Power. Watts. W. Ohm's law: Voltage = Current x Resistance. Power law: Power = Voltage x Current. Set any two, and the other two can be calculated.