What Is a Resistor?

A resistor is a passive electronic component that opposes the flow of electric current. Its resistance is measured in ohms (Ω).

Resistors are used for current limiting, voltage division, biasing, signal conditioning, feedback and many other electronic functions.

Carbon Film Resistors

Carbon film resistors are common general-purpose components. They are inexpensive and suitable for many low-power electronic circuits.

Metal Film Resistors

Metal film resistors generally provide better tolerance and stability than many basic carbon film resistors. They are commonly used where more accurate resistance values are useful.

Wirewound Resistors

Wirewound resistors are made by winding resistance wire around a suitable core. They can be manufactured for relatively high power levels and are useful in applications where significant heat must be handled.

Power Resistors

Power resistors are designed to dissipate more heat than ordinary small signal resistors. They may be physically larger and are often used in power supplies, amplifiers, motor circuits and load banks.

Variable Resistors

Variable resistors allow their resistance to be adjusted. Potentiometers and trimmer potentiometers are common examples.

Potentiometers are frequently used as volume controls, adjustment controls and voltage dividers.

Resistor Tolerance

Tolerance specifies how much the actual resistance can differ from the nominal marked value.

For example, a 1 kΩ resistor with 5% tolerance can have an actual resistance within the specified tolerance range around 1 kΩ.

Power Rating

The power rating indicates how much electrical power the resistor can dissipate under its specified conditions.

The basic resistor power relationship is:

P = I²R

and also:

P = V²/R

Common Resistor Types

Type	Typical Use
Carbon film	General-purpose circuits
Metal film	Accurate and stable circuits
Wirewound	Higher-power applications
Power resistor	High heat dissipation
Potentiometer	Adjustable resistance
Trimmer	Calibration and adjustment

Conclusion

Choosing a resistor involves more than selecting the resistance value. The resistor type, tolerance, power rating, physical size and application should all be considered.