The nominal impedance Z = 4, 8, and 16 ohms (loudspeakers) is often assumed as resistance R Ohm's law equation (formula) V = I × R and the power law equation (formula) P = I × V P = power, I or J = Latin influare, international ampere, or intensity and R = resistance V = voltage, electric potential difference Δ V or E = electromotive force (emf = voltage)