They are parts used in electrical circuits whose main function is to convert electrical energy into thermal energy, that is, they are used as heaters or as heat sinks.

Some examples of resistors used in our daily lives are: the filament of an incandescent lamp, the heater of an electric shower, the filaments that are heated in a greenhouse, among others.

In theoretical electrical circuits it is usually considered all the resistance found from resistors, that is, the connections between them are considered as ideal conductors (without resistance), and the representations are used: