Electric Power

A hair dryer trips a breaker because it draws a lot of current, and current is what breakers watch. Power is the rate of energy delivery, measured in watts, and it depends on both how much charge moves per second (current) and how much energy each unit of charge carries (voltage). A phone charger sips maybe 5 watts. A hair dryer gulps over a thousand. Same outlet, same 120 V, wildly different current, because P = IV means current has to scale with power when voltage is fixed.

Inside a resistor, moving charges collide with the atoms of the material and lose energy to those collisions. That lost energy becomes heat, and in a filament it becomes light too. The three power formulas, P = IV, P = I^2R, and P = V²/R, all describe this same energy loss, just rearranged using Ohm's law so you can use whichever two quantities you already know. Pick the version that matches your given values and you skip an extra step.

This connects directly to why adding bulbs to a circuit changes their brightness. In series, more resistance means less current flows everywhere, so each bulb's I^2R drops and they dim. In parallel, each bulb still sees the full voltage, so adding one doesn't dim the others, but it does pull more total current from the source. Power is the quantity that ties current, voltage, and resistance back to something you can feel: heat, light, a breaker tripping.