residtors are used to limit current flowing to a device or to limit voltage for other compo-nents, or to serve as circuit. Resistors may be classified as fixed or variable in their types. Some common resistance components are as follows : heating elements , resistors ( fig. 6-1), varia-ble resistors , thermistors ( fig. 6-2) , light-dependent resistors ( ldrs, fig. 6-3) and diodes.