Variable Resistors: Definition, Working, Formula, and Applications

A variable resistor is a type of resistor whose resistance can be changed as per the requirement. The variable resistor permits the change in the current or voltage in an electric circuit as per Ohm’s law.

The term ‘variable’ means ‘changing’. Thus, the resistance of a variable resistor can be varied as per the requirements of the circuit. Variable resistors are important components for various electronic devices like volume controllers, voltage regulators, and calibration devices.

In this article, we will discuss variable resistors and will cover their various concepts, such as definition, working principle, circuit symbols, formula of resistance, and applications.

What is a Variable Resistor?

A variable resistor is a passive circuit element used in electrical and electronic circuits and devices to insert a resistance that can be changed as per requirements. It is also known as a potentiometer. It is simply a resistor which has an adjustable resistance.

It controls the strength of the electric current flowing in the circuit by changing its resistance value.

The circuit symbol a variable resistor is shown in the following figure.

symbols of  variable resistors

Working Principle

We get variation in the resistance by changing the effective length. This means the resistance of a variable resistor is changed by varying its length by some means.

A variable resistor typically consists of a long resistive element and a movable contact terminal called a wiper. The wiper can be moved along the length of the resistive element to adjust its effective length to change its resistance.

How to Calculate Resistance of Variable Resistor?

The value of the resistance depends on the position of the wiper on the resistive element.

variable resistance calculation

We can use the following formula to compute the resistance of a variable resistor for a given wiper position on the element:

formula for  Resistance of Variable Resistor

Where R is the resistance of the variable resistor in ohms for a given wiper position, R1 is the resistance of the element between ‘x’ and ‘y’, l is the total length of the element, and l1 is the distance between the wiper and end ‘y’ of the element.

For example, if a variable resistor has 100 Ω between ends ‘x’ and ‘y’. The total length of the element is 10 m. If the wiper is placed at a position on the element, where the distance between the point ‘y’ and the wiper is 4 m. Then, calculate the effective resistance.

Here, R1 = 100 Ω, l = 10 m, l1 = 4 m. Then, the resistance R of the resistor for the given wiper position will be,

numerical problem

Hence, it offers a resistance of 60 Ω for the given wiper position.

Advantages of Variable Resistor

The following are some important advantages.

  • They provide flexibility in the circuit, as it provides a variable resistance that can be changed as per need.
  • It provides precise and continuously adjustable resistance in the circuit.
  • They can be fixed easily into an electronic circuit.
  • They provide a cost-effective solution for adjustable resistance in a circuit.
  • It is a highly versatile component, as it can be used in various types of electronic circuits and devices.

Applications of Variable Resistors

The following are some key applications.

  • Used in electronic circuits to control the strength of the electric current. They act as a potentiometer and control the output voltage across the audio device. Logarithmic-type resistors are better than linear ones because they exactly match the human perception of loudness.
  • Used in fan regulators for speed control purposes.
  • They are also used in light dimmer switches to control the intensity of light produced by the lamps.
  • Applications in power supplies to regulate their output voltage and currents.
  • Used in audio devices and systems to control the volume, bass, and tone of the output sound.
  • Applications in various types of calibration devices and sensors for fine calibration of different types of instruments.
  • Used for adjusting the color, brightness, contrast, and position of the picture on a television screen.
  • They are used to control the speed, torque, and direction of motors, servos, fans, pumps, etc. 


In conclusion, in this article, we have described all the major concepts of variable resistors, including definition, working principle, formula, and applications. This resistor is a crucial circuit element used in various electronic circuits and devices to adjust the amount of voltage and current and its application increases the flexibility in circuit design by providing an easily adjustable resistance.

Leave a Comment