What is a Resistor – Definition, Symbol, Types, and Applications

This article describes the resistor, resistor definition, its symbol, types, and applications in various electrical and electronic circuits.

Resistor Definition

The resistor is a passive electrical component that opposes the flow of electric current. The passive property of the resistance causes it to consume the electric energy in the form of heat, and thus, it does not deliver the electrical energy. The opposition of the electric current by a resistor is called resistance, and it is denoted by the Ohm, and the symbol R represents resistance. The resistor is widely used in circuits to limit the current.

Working of Resistor

The electrons flowing through the resistor collide with the positive atom of the resistor’s material, and electrons collide with each other inside the resistor. The collision produces heat inside the resistor, and it is dissipated through the resistor’s body. This behavior of the electrons in the resistor causes a reduction in the speed of the electrons. Thus, the number of electrons crossing per unit area reduces. The reduction in the number of electrons causes a reduction in circuit current.

Types of Resistors

There are two types of resistors.

  1. Fixed Resistors
  2. Variable Resistors

(1). Fixed Resistor:

The resistance value of the fixed resistor remains constant. The resistance value of the fixed resistor is fixed by selecting the proper length and cross-section area during the design stage. These resistances are available in standard resistance values. The following figure shows the symbol of a fixed-type resistor.


The following are the types of fixed resistors.

  • Carbon composition resistors,
  • Carbon film resistors,
  • Metal-oxide film resistors,
  • Metal film resistors,
  • Wire wound resistors,
  • Surface mount resistors, etc.

(2). Variable Resistor:

As its name implies, the resistance of the variable resistor can be varied by changing the length or cross-section area. The resistor has three connecting terminals. Two connections are connected at both ends of the resistor, and the third connection is connected to the slider contact.

Moving the slider over the resistor’s body decreases its length. The change in the length causes the resistance value to reduce. We know that the resistance value is proportional to the length and inversely proportional to the cross-section area. The following figure shows the symbols of the variable resistor.


The variable resistors are available in wire wound and composition type. A potentiometer or pot has a three-terminal element with a slider arrangement. We can adjust the resistance by adjusting the slider.

Are resistors linear or non-linear devices? The resistor is a linear device as far as it follows Ohm’s law under certain conditions. However, resistors can have non-linear characteristics under certain conditions. Therefore, on the basis of this, resistors can be further categorized into;

  1. Linear Resistor
  2. Non-linear Resistor

(1). Linear Resistor Definition

If the current through the resistor increases in the same proportion as the increase in voltage, then we can say that the resistor is a linear resistor. If you draw a graph between voltage and current, you will get a straight line with a slope of 1/R for a linear resistor. Thus, the linear resistor definition is the resistor whose current linearly varies with the applied voltage.

The V-I characteristics of the linear resistor are shown in the below image.


The above graph shows that the resistor following Ohm’s law is linear.

(2). Non-Linear Resistor Definition 

Compared to linear resistors, non-linear resistors do not follow Ohm’s law. The graph between the voltage and current exhibits non-linearity, and the resistors with this property are known as non-linear resistors. The incandescent lamp and most of the semiconductor devices like diode, transistors, etc. have nonlinear resistance.

The following image shows the voltage and current characteristics of non linear resistor. The nonlinear resistors do not have a straight line, and their slope is not constant.


Applications of Resistors

The resistor is the basic building block of the electrical and electronic circuits. The following are the applications of resistors.

  • Current limiting applications in the electrical and electronic circuits
  • Dynamic braking of motors
  • Speed control of motors
  • Audio circuits
  • Video Circuits
  • light dimmer circuits
  • Fan regulators
  • Crane operation
  • Heating element

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