A resistor works by restricting the flow of current, it can do this in one of three ways: firstly, by using a less conductive material, secondly by making the conductive material thinner and finally by making the conductive material longer. A lot of resistors are wire-wound, as the name suggests they consist of a conductive wire wound around an insulating middle, with other resistors rather than a physical wire wound around, it’s just a spiral of carbon, these are called carbon-film. Wire-wound resistors are more precise and stable than carbon-film resistors, the resistance of the resistor is controlled by the number of turns and thickness of the wire. There are many types of resistors but they all function on the same three principles as this is the only reliable way to control the resistance of the resistors.