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

In this article, we shall discuss resistors, their definition, circuit symbol, types, and applications in various electrical and electronic circuits.

What is a Resistor?

A passive circuit element that is used to introduce electrical resistance in an electrical or electronic circuit is called a resistor. It is a passive circuit component as it only consumes electrical energy, and does not deliver electrical energy. The measurement of opposition that a resistor offers in the flow of current through it, is called resistance. The resistance is represented by the symbol R.

The resistor is a circuit element used to model the current-resisting behaviour of a material. We may also define the resistor in terms relation between voltage and current as, a circuit element for which the voltage across the element is directly proportional to the current through it, then the element is called a resistor.

Working of Resistor

In a resistor, electrons moving under the influence of an electric field collide with positive atoms of the resistor material again and again. After each collision, these electrons slow down and the number of electrons crossing per unit area is reduced. Consequently, the current through it is reduced, and the energy released on each collision is dissipated in the form of heat. In this way, a resistor opposes the flow of electric current.

Types of Resistors

The resistors can be of the following two types, namely-

• Fixed Resistors
• Variable Resistors

(1). Fixed Resistor:

A resistor whose resistance remains constant is called a fixed resistor. It is the most widely used type of resistor. These are mainly used in electronic circuits to introduce a constant resistance in a circuit. The resistance value of fixed resistors is determined during their manufacturing, and these resistors come in standard resistance values. The circuit symbol of the fixed resistor is shown in figure-1.

There are several types of fixed resistors available such as carbon composition resistors, carbon film resistors, metal-oxide film resistors, metal film resistors, wire wound resistors, surface mount resistors, etc.

(2). Variable Resistor:

A resistor whose resistance value can be adjusted as per requirement is called a variable resistor. A variable resistor consists of two main parts viz. an element of fixed resistance and a slider. The slider taps onto the fixed resistor element. Therefore, a variable resistor has three connection terminals – the two terminals are of the fixed resistor element and the third is the slider terminal. When we are required to provide a resistor with variable resistance, one end of the fixed resistor element and the slider terminal are connected in the circuit. The circuit symbol of the variable resistor is shown in the figure-1.

The variable resistors can also be of either wire-wound or composition type. A most commonly used variable resistor, called a potentiometer or pot, is a three-terminal element with a slider. By sliding the slider, the resistance between the slider terminal and the fixed terminals can be adjusted.

Depending upon Ohm’s law, resistors may also be classified into two types, namely-

(1). Linear Resistor – 

A resistor that obeys Ohm’s law is known as a linear resistor. A linear resistor always has a constant resistance and hence its current-voltage characteristic is a straight line passing through the origin as shown in figure-2.

(2). Non-Linear Resistor – 

A resistor that does not obey ohm’s law is known as a non-linear resistor. The resistance of a non-linear resistor varies with the current through it. Therefore, the current-voltage characteristic of the non-linear resistors is not a straight line, i.e. it has a different slope at different points. The figure-3 shows a current-voltage characteristic of a typical non-linear resistor. Examples of devices with non-linear resistive behaviour are the electric light bulb and the diode.

Although, all practical resistors may exhibit non-linear resistive behaviour under certain conditions.

Applications of Resistors

The resistor is one of the fundamental components in electrical and electronic circuits. The primary use of the resistor is to control the flow of electric current in a circuit. The following are some major applications of resistors-

• Resistors are used in different circuit functions like speed control of a motor, changing the loudness of an amplifier, etc.
• Resistors are used for designing voltage divider circuits.
• Resistors are used in electric heating appliances as the current passing through a resistor generates heat.
• Resistors are used in light-dimming circuits.
• Resistors are also used in fan regulators, etc.

Conclusion

In this article, we discussed resistors, their types, and their applications. From the above discussion, it is clear that a resistor is a two-terminal passive circuit element that is used in various electrical and electronic circuits to introduce a certain amount of electrical resistance. The main use of a resistor in a circuit is to control the current through it.