What is Resistor?

The device which allows us to introduce a controlled amount of resistance into an electrical circuit is known as a resistor. The most important and commonly used components in an electronic circuit are the resistors.

The basic idea is known to all about how electricity flows through an electronic circuit. Here, two categories can be identified viz: – conductors and insulators. Insulators do not allow the flow of electrons, but the conductor does. However, the resistor determines the amount of electricity that is allowed to pass through them. The total voltage passes through when it is passed through a conductor like the metal; by introducing the resistors, the amount of voltage and current can be controlled. 

The ease at which the electrons will allow the electricity to flow through it is known as resistance.

An insulator has better resistance than the conductor, and the term resistance is defined as the electrical quantity used by the resistor to control the flow of electrons.

What is Resistance?

Based on Ohm's law named after German Physicist Georg Simon Ohm, the resistance is defined

As per the Ohm's Law, the voltage [V] across a resistor is directly proportional to the current [I] flowing through it. Here, the resistance [R] is constantly proportional.

Therefore, V = I * R

Resistor Unit

The SI-unit of resistance is known as Ohm [Ω]. Kilo ohms [KΩ], megaohms [MΩ], milliohm and so on are known as the higher multiple and sub-multiple values of Ohm

The voltage required for creating 1 ampere of current to flow through the circuit is known as the resistance. For example, if we have to create 1 ampere of current flow through a circuit by 100 volts, then the resistance is 100 ohms.

Resistor Symbol

The resistor is a 2 terminal passive device. The resistor symbol is given below.

How Does a Resistor Work?

Water flowing through the pipe can be used as an example to explain the working of the resistor. Consider a pipe through which the water flows. Now, as the diameter of the pipe is reduced, the flow of the water will be reduced. Further, as the pressure is increased, the force of the water is increased, and energy is dispersed as heat. With this example, the force applied to the water is similar to the current flowing through the resistance. The voltage can resemble the pressure applied.

Working Principle of Resistor

The resistor absorbs the electrical energy in the process where it acts as a hindrance to the flow of electricity by reducing the voltage, and it is dissipated as heat. In today's world of electronic circuits, the heat dissipation is typically a fraction of a watt.

Ohm's law states that if I is the current flowing through the resistor in amperes, and R is the resistance in ohms, then V is the voltage drop that is imposed by the resistor (it is the electrical potential difference between the two contacts that are attached.)

V = I / R

Another way of saying this is that the 1Ω resistor will allow a current of 1amp when there is a capacity difference between the ends of the resistor is 1 volt. 

If P is the power in watts dissipated by the resistor, in a DC circuit:

P = V * I

By substitution in Ohm's law, we can express power (watts) in terms of current and resistance:

P = I 2 / R

We can also express power (watts) in terms of voltage and resistance:

P = V^2 * R

These alternative equations can be used when you do not know the value of the voltage drop or the current, respectively.

Approximately similar relationships exist when using alternating current, although the power will be a more complex function of the resistor.

Resistor Series and Parallel Circuits

There are cases in which an electrical circuit might have two or more resistors. They can be connected in series and parallel ways.

The resistors when connected in the series path, is known as a series connection, and the current flowing through them will be the same. The sum of the voltage across each resistor will be equal to the voltage across the resistors. Here is a diagram of resistors connected in series. In a series connection, the three resistors R1, R2, and R3 and total resistance R(total) is given by:

Rtotal = R1 + R2 + R3

The series in which the resistors are connected in a parallel is known as a parallel connection. Here, the voltage applied across each component remains the same. The sum of the currents across each resistor is equal to the current across the series.

The below diagram shows the parallel-series connection of resistors

Here, the three resistors named R1, R2, and R3 are connected.

The total resistance R(total) is given by

(1/ R1 + 1/ R2 + 1/ R3) = 1/ R total.

Therefore, Rtotal = (R1 * R2 * R3)/ (R1 + R2 + R3)

Power Dissipated in a Resistor

The below equation will give you the value of the power dissipation through a resistor.

Power P = I­^2 * R = V * I = V^2 /R

The first equation was obtained from Joule's first law, while the other two were derived from Ohm's law.


During the study of electricity, you discover the materials that are used, which are categorized into two basic categories, namely conductors and insulators. The substance such as metal through which the electricity flows is known as a conductor. Besides, the material like plastic and wood through which the electricity doesn't flow is known as an insulator. But it is not as simple. Electricity can be conducted through a substance if it can flow significant voltage across it: even air, which is considered as an insulator, can become a conductor when powerful voltage builds up in the clouds, which causes the lightning to happen.

If you want to understand the ease with which electricity flows, it is better to talk about the resistance rather than discussing insulators and conductors. As compared to the conductor, the insulator has a much higher resistance. 

FAQ (Frequently Asked Questions)

1. What is the Classification of Resistor?

From an operating standpoint, resistors are been classified as:

1.  Fixed resistors

2.  Adjustable/variable resistors

1. Fixed resistors are further categorized as:

a. Carbon composition resistor – This is the most common one and its resistive substance is made of carbon clay and leads of tin copper.

b.  Metalized resistor – This substance like constantan is 60% copper and 40% nickel, and magnesium material possesses a high-level of resistivity.

c.   Wired wound type resistor – It is made through a film deposition technique using thick film of resistive material into the insulating substance.

2. Variable resistor is used for circuits requiring that it can be adjusted to remain connected with the circuit frame. They generally have three lead viz: two fixed and one movable.

2. What is the Colour Coding of Resistor?

With the help of the color-coding, one can find the value of the resistance. The band of colors is shown in the outer covering of the resistor.

Given below is the list of colors and associated numbers