A resistor is a specialized electrical component that provides resistance as a circuit element. Resistors are passive, which means they are not affected by the current they carry.
Resistors have two primary functions within a circuit:
- Reduce current flow
- Lower voltage
Resistors are usually made of metal or carbon wire. They are designed to keep a constant value when in use and produce heat instead of light when used inside an electrical component. As the circuit works, resistors dissipate heat, which is not used. On the other hand, the metal portion of a light bulb is a type of resistor that does emit light.
There are three types of resistors:
Fixed resistors are the most common. They can be found inside many different types of electronic components and serve to protect them from too much current flow.
Traditional variable resistors are continually altered as they work. A common type of variable resistor is found in the volume control on a radio. Another type of variable resistor is called a potentiometer, or a pot. Pots are usually small and work by having their resistance control adjusted once and fixed, often with a screwdriver.
Two common types of special resistors include light-dependent resistors, which change resistance as light levels change. Similarly, thermistors change resistance as the temperature changes.