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Resistor

physical science Maturity 11-13 Next article →

A resistor is a passive, two-terminal electronic component. It works by implementing electrical resistance within a circuit.

Carbon and ceramic resistors of different power ratings
Carbon and ceramic resistors of different power ratings

This component is essential for managing how electricity behaves. Engineers use resistors to reduce current flow or adjust signal levels. They also use them to divide voltages or bias active elements. Resistors are ubiquitous, meaning they are found everywhere in electronic equipment.

3 Resistors
3 Resistors

To understand how a resistor works, we can use the hydraulic analogy. Imagine water flowing through a system of pipes.

ResistanceHydraulicAnalogy2
ResistanceHydraulicAnalogy2

If a pipe becomes clogged with hair, the water flows more slowly. It requires much higher pressure to maintain the same flow through the clog. Electricity behaves in a very similar way. Pushing current through a large resistance is like pushing water through a clogged pipe. It requires a larger push, known as voltage, to drive the same amount of electric current.

Scientists use Ohm's law to describe this relationship mathematically. This law states that the voltage across a resistor is proportional to the current passing through it. The constant of proportionality is the resistance itself.

Resistor symbol America
Resistor symbol America

The standard unit for electrical resistance is the ohm, represented by the symbol Ω. This unit is named after the scientist Georg Simon Ohm. Because resistors cover a massive range of values, we use derived units. These include the milliohm (1 mΩ) for small values and the megohm (1 MΩ) for very large ones.

Resistor symbol Europe
Resistor symbol Europe

Resistors can be organized into different types of networks. In a series connection, resistors are placed end to end. The total resistance of a series circuit is the sum of each individual resistance value.

resistors in series
resistors in series

In a parallel connection, resistors are placed side by side. The total resistance in parallel is calculated as the reciprocal of the sum of the reciprocals of the individual resistors.

resistors in parallel
resistors in parallel

Some networks combine both series and parallel connections. These complex networks may require sophisticated methods like the Y-Δ transform to solve.

When current flows through a resistor, electrical energy is converted into heat. This process is called power dissipation.

The power consumed is calculated by multiplying the voltage by the current. If a resistor's average power dissipation exceeds its maximum rating, it may suffer permanent damage. This can change its resistance or even cause the component to burn.

Danotherm HS50 power resistor
Danotherm HS50 power resistor

Excessive heat can also damage the circuit board or start a fire. To prevent this, some engineers use flameproof resistors that will not produce flames during an overload.

There are many different physical types of resistors. Fixed resistors have a resistance that stays mostly constant regardless of temperature or time. Variable resistors can be adjusted, such as a volume control or a lamp dimmer.

Potentiometer cutaway drawing
Potentiometer cutaway drawing

One historical type is the carbon composition resistor. These consist of a mixture of powdered carbon and an insulating material like ceramic.

Old Radio Resistors
Old Radio Resistors

While they can withstand high overloads, they are less popular today because they lack stability. They can also change value if they are exposed to high humidity or heat during soldering.

Resistors are also categorized by their form factor and mounting style. Some components are axial, meaning their leads come off the body in a straight line. Others are radial, with leads coming off the sides.

3 Resistors
3 Resistors

Modern electronics often use Surface Mount Technology (SMT) for very small components. Resistors are also found inside integrated circuits rather than as separate parts. Whether they are large power resistors or tiny surface-mount parts, they are the foundation of modern electrical systems.

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🖼️ Images & Media (23)
File:Resistor symbol America.svg
Resistor symbol America.svg
File:Resistor symbol Europe.svg
Resistor symbol Europe.svg
File:Carbon and ceramic resistors of different power ratings.jpg
Carbon and ceramic resistors of different...
File:ResistanceHydraulicAnalogy2.svg
ResistanceHydraulicAnalogy2.svg
File:resistors in series.svg
resistors in series.svg
File:resistors in parallel.svg
resistors in parallel.svg
Resistor warming thermal video.webm
File:Danotherm HS50 power resistor.jpg
Danotherm HS50 power resistor.jpg
File:USSR power resistor VZR 12W.JPG
USSR power resistor VZR 12W.JPG
File:Sil resistor.png
Sil resistor.png
File:3 Resistors.jpg
3 Resistors.jpg
File:Résistances anciennes annees 50.jpg
Résistances anciennes annees 50.jpg

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