Junior Officer Surface Material Readiness Course Practice Test

Power in a DC circuit comes from the product of the driving force and the flow of charge. In this formula, E stands for voltage (the electromotive force) and I stands for current (the rate of flow). Multiplying voltage by current gives power, with the units volts times amperes equaling watts. If you bring in resistance, you’d substitute voltage using Ohm’s law (V = I × R), which leads to P = I^2 × R—a different, but equivalent, way to calculate power when you know current and resistance. The combination of current and resistance would give voltage, not power, in the original form, and multiplying power by current doesn’t fit the basic P = E × I relationship.