Electric power is just voltage times current, until alternating current complicates things
A watt is one joule of energy moved every second, and in a simple circuit you find the power by multiplying voltage by current. That tidy rule hides some oddities: electrons actually travel the opposite way to the current on a diagram, and in AC circuits some energy just sloshes back and forth.
Power is the rate at which work is done. Voltage is the work needed to push one unit of charge between two points, and current is how much charge passes per second, so their product gives watts. For a simple resistor, combining that with Ohm's law yields equivalent forms: current squared times resistance, or voltage squared divided by resistance. Convention says current flows the way positive charge would move, but the charge carriers in wires are negatively charged electrons drifting the other way; the two descriptions are equivalent.
Every component is either a source or a load. In a generator or battery, charges are forced uphill against the electric field, turning mechanical or chemical energy into electrical energy. In a bulb, motor or heater, charges run downhill and give that energy up as light, motion or heat. A rechargeable battery switches roles: a source while running a device, a load while on its charger. Engineers count power flowing into a component as positive, which gives loads positive consumption and sources negative.
Alternating current reverses twice every cycle. With pure resistance nothing changes, but coils and capacitors store energy and hand it back each cycle. The part that does useful net work is real power; the part that merely oscillates is reactive power; and multiplying the RMS voltage by the RMS current gives apparent power. The three form a right triangle, and the ratio of real to apparent power, the power factor, always falls between minus one and one.
Michael Faraday worked out the principles behind most generation in the 1820s and early 1830s, and moving a wire loop between magnet poles is still how power stations make electricity, whether driven by burning fuel, nuclear fission, water or wind. Alessandro Volta built the first battery in 1800. A nation's electricity use per person tracks its industrial development.
Source: Electric power
