What is variable resistor?

A resistor whose resistance value can be adjusted as per requirement is called as Variable Resistor. It is basically an electro-mechanical transducer, which varies resistance by sliding contacts (wiper/slider) over a resistive element. The two most common used variable resistors are Rheostat and Potentiometer. We will see each of them in details.

Potentiometer (POT)

We usually refer Potentiometer as a POT. These POT are available in different values. The basic form of POT can represented as:

Circuit Symbol of Potentiometer
Circuit Symbol of Potentiometer

Features of Potentiometer

  • Total no. of terminals = 3
  • It can be seen as two resistors in series, where the slider position determines the resistance ratio of two resistors.
  • It divides voltage in ciruit. Hence it is also called as adjustable voltage divider. It is constructed as composition type resistor.
  • It has high working efficiency
  • It has high resolution as compared to Rheostat.

The potentiometer can be used in two configurations.learn-embedded-system

Voltage Divider Circuit

This type is used to control the amount of input voltage passing to output.

POT as Voltage Divider
POT as Voltage Divider


The basic form of Rheostat can represented as:

Circuit Symbol of Rheostat
Circuit Symbol of Rheostat

Features of Rheostat

  • Total no. of terminals = 2
  • It can be seen as a single variable resistor
  • It controls current flow in circuit. Hence it is constructed as wire wound resistor.
  • It has low working efficiency
  • It has low resolution (change in resistance w.r.t change in slider position)


It is a sub type of rheostat. The name itself implies meaning of resistor “Pre + set = Variable resistor already set to a definite value”It has two terminals and used where no need of repetitive resistance adjustment. When resistance adjustment is needed only at circuit designing stage and at normal use, then preset resistor is used. It is also called as ‘set and forgot’ or ‘Trimmer’ resistor.

This is it for this post. I believe now you’re familiar with variable resistor and its significance. There are voltage and current divider circuits. We’ll discuss them in our future post. Thanks for reading.

Get Free Courses & Webinars
You'll receive only high quality learning material, tips & tricks
I agree to have my personal information transfered to MailChimp ( more information )
We respect your privacy

About Roshankumar Bhamare

Roshankumar Bhamare received the Master degree in Electronics and Telecommunication engineering. He is currently a Lecturer in Engineering College. He is life member of Indian Society for Technical Education (ISTE). He is also a co-author of BINARYUPDATES.COM. His current interests include Electronics Design Automation (EDA) tools, Microcontroller based circuits.


Register | Lost your password?