Summary
Resistors are used to cause a drop in voltage in circuits. They are used to control current flow.
Resistors are electrical components that resist a current running through them.
Putting a resistor in a circuit causes a drop in voltage across the resistor. So resistors are commonly used to control the voltage that reaches various components.
It is also important to remember that each electrical component also has a resistance of its own.
Most resistors that can carry large currents contain a coil of high-resistance wire wound around a ceramic former to dissipate heat.
Resistance is measured in ohms, represented by a Greek letter, omega, and so resistors are rated in ohms as well, to indicate how strongly they will oppose any current flowing through them.
Resistors also have a wattage rating. This is because resistors work by converting some of the electrical energy passing through them into heat.
Some types of resistors and examples:
- Fixed resistors are generally cylinders with connecting metal leads projecting along the axis of the cylinder at each end. Most 'axial' resistors carry a series of colored stripe markings, to indicate the amount of its resistance and its tolerance. Fixed resistors can be manufactured as very tiny devices without leads, and can be built into integrated circuits with many other miniaturized components.
- Variable resistors can be adjusted with a control so that the resistance changes, and are called rheostats or potentiometers. An audio volume control knob on an amplifier would be an example of a potentiometer.
- Thermistors are temperature-dependent resistors. There are two main types depending on whether the resistance of the device increases or decreases as the temperature rises.
- Metal Oxide Varistors have two different resistance values: a high resistance at low voltage and a low resistance at high voltage. The 'trigger voltage' of a varistor is the point at which its resistance changes.
