A diode is an electrical switch commonly made of semiconductor material, such as silicon. It consists of two terminals: positive (anode) and negative (cathode). It is often used as a rectifier, which is a device that converts AC to DC with current flowing in one direction. Rectifiers can be found in electronic components such as radios, DC power supplies and high-voltage transmitters. Diodes take on many forms, such as vacuum tube diodes, semiconductor diodes and mercury-arc valves. A diode operates in conjunction with a resistor within a circuit.