This chapter looks at some of the many components used in electronics. There are three types of resistors in common use: carbon, wire wound and carbon preset or variable. The wire-wound type is usually chosen where high voltage is present. It is also more accurate than the carbon variety. The most common, apart from actually writing the value on the capacitor, is to use the same colour code as for resistors. The types of inductors and transformers used in electronics work on the same principles. Probably the main difference is the use of ferrite as a core for inductors that are used to tune for radio frequencies. Most electricity supply systems are alternating current (a.c.) and since many appliances require a direct current (d.c.) supply, it is necessary to change a.c. to d.c. Unlike installation circuits, electronic circuitry is almost entirely constructed using soldered joints. The formation of such joints is critical to ensure healthy circuit performance.