Resistor

Introduction

A resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element. In electronic circuits, resistors are used to reduce current flow, adjust signal levels, to divide voltages, bias active elements, and terminate transmission lines, among other uses.

A close-up view of a variety of resistors.

History

The concept of resistance was first studied by Georg Simon Ohm in 1827. He discovered that the current passing through a conductor between two points is directly proportional to the voltage across the two points, introducing the concept of resistance and Ohm's law.

Construction and Composition

Resistors are typically constructed of metal wire or carbon and are designed to maintain a stable resistance value over a wide range of environmental conditions. The resistance material is often wrapped in a protective casing to protect it from physical damage and environmental effects that could alter its resistance.

A resistor cut open to reveal its internal construction.

Types of Resistors

There are many different types of resistors, each with its own specific characteristics and uses. Some of the most common types include fixed resistors, variable resistors, and special purpose resistors.

Fixed Resistors

Fixed resistors are the most common type of resistor. They have a predetermined resistance value that cannot be changed. They are often used in circuits where a specific amount of resistance is needed.

Variable Resistors

Variable resistors, also known as potentiometers or rheostats, have a resistance value that can be adjusted. They are often used in volume controls and other adjustable circuits.

Special Purpose Resistors

Special purpose resistors are designed for specific applications. For example, a thermistor's resistance changes with temperature, making it useful for temperature sensing circuits.

A variety of different types of resistors.

Resistor Color Code

The resistor color code is a standard way of showing the resistance value of a resistor. It uses a series of colors to represent numbers, which are then used to calculate the resistance.

Resistor Networks

Resistors can be combined in series and parallel to create resistor networks. These networks can be used to create a wide range of resistance values and to distribute electrical power throughout a circuit.

A circuit diagram showing a resistor network.

Applications

Resistors are used in virtually every electronic device. They are essential components in circuits and are used to control voltage and current levels, among other things.