Resistors are a type of passive electronic component that limits the flow of electrons through a circuit. Passive components can only consume power and cannot generate it. Resistors can be fixed or variable, but their resistance is always measured in ohms, which is represented by the greek capital-omega (Ω). Variable resistors are also known and categorized as potentiometers. Resistors are used in a variety of applications, including limiting electric current, voltage division, heat generation, matching and loading circuits, gain control, and setting time constants.