Plot a graph of voltage, V on the y-axis v current, I, on the x-axis. For a filament bulb, voltage and current are not directly proportional as the graph is not a straight line through the origin.

In other words, the watt's law formula is expressed as: Power = Voltage × Current. This simple equation is essential for understanding how electrical components consume and distribute energy in a ...

An example is a filament lamp. As current increases, the filament gets hotter and the resistance of the bulb increases. A thermistor is a device that’s resistance changes with temperature.