Conductors and Insulators are the two broad categories among which almost all matter can be classified based on its behavior towards the electric current. It is very important for us to understand the electrical properties of materials as it helps us in the design of various electrical circuits and devices. A device’s efficiency is very much dependent on the kind of material that is being used. What are conductors and insulators? How are they different from each other? How do they help in the design choice of various electrical devices? All these questions can be answered by exploring the world of conductors and insulators with the help of this article.

Definition of Conductors

A conductor is a material that allows the flow of current through itself with ease. Any metal is essentially a conductor. At an atomic level, we can say that a conductor is a material that has a large number of electrons. These electrons can move throughout the material and are responsible for the flow of current.

What Makes a Material Conduct Electricity?

An atom has many electrons spinning around the nucleus. The outermost electrons are called valence electrons. They have the least attraction towards their nucleus. So these valence electrons can be easily stripped out from their parent atoms. Once loose, these valence electrons (now known as electrons) can movely throughout that material. As a result, current can flow easily through them. Such materials are called conductors.

Examples of Conductors

Conductors are used in making wires to pass electric current. The wires that bring electricity to our homes and the various gadgets we use are made of metals. Most metals are good conductors. However, there are non-metals also that conduct electricity. The human body is also a good conductor, and current can pass through our bodies, giving us a shock.
Some of the good conductors are:
a. Silver
b. Copper
c. Gold
d. Aluminium
e. Mercury
f. Platinum
g. Graphite
h. Saltwater

Definition of Insulators

Insulators are materials that do not allow the flow of current through them. In such materials, the electrons are very tightly bound to their parent atoms so there are hardly any electrons to conduct electricity.

Examples of Insulators

Insulators are used in making the coverings of wires so that two wires do not touch each other or pass current to our hands. The outer covering of many electrical gadgets, machines are made of insulators. As a result, the current does not flow everywhere but is restricted to only the conducting wires.
Some of the good insulators are:
a. Rubber
b. Wood
c. Plastic
d. Glass
e. Air
f. Oil

Resistivity and Conductivity

Resistivity or Specific Resistance

We define resistivity or specific resistance \((ρ)\) as the resistance offered by a material of dimensions \(1\,\rm{m} \times 1 \,\rm{m} \times 1 \,\rm{m}\). It means that the resistivity of a material is numerically equal to the resistance of the resistor made out of that material having a length of \(1\,\rm{m}\) and a cross-sectional area of \(1\,\rm{m}^2\). The resistance of a conductor is given by the following equation.
\(R = \frac{{\rho l}}{A}\)
Here,
\(R\) is the resistance of the conductor,
\(l\) is the length of the conductor,
\(A\) is the area of cross-section of the conductor, and
\(ρ\) is the resistivity of the material.
Rearranging the above equation we get,
\(\rho = \frac{{RA}}{l}\)
The unit of resistivity can be found out as shown below.
\(\rho = \frac{{RA}}{l} = \frac{{{{\Omega \times }}{{\text{m}}^{\text{2}}}}}{{\text{m}}}{=\Omega \text{m}}\)

Conductivity

Simply put, the reciprocal of resistivity is known as conductivity. Mathematically it is given by the following relation.
\(\sigma = \frac{1}{\rho }\)
Similarly, the reciprocal of resistance is known as conductance. Mathematically it is given by the following relation.
\(G = \frac{1}{R} = \frac{A}{{\rho l}} = \frac{{\sigma A}}{l}\)
The unit of conductance is \(\rm{Ω}^{-1}\) which is known as siemens. The unit of conductivity is \(\rm{Ω}^{-1} \rm{m}^{-1}\) or siemens per metre.
The specific resistance of some materials are given below:

From this table, we can see that specific resistance is very high in materials such as glass, rubber, wood, making them good insulators.

Difference between Conductors and Insulators

Conductors	Insulators
They have less resistance.	They have more resistance.
They allow more current through them.	They allow less or negligible current.
There is a movement of electrons in them.	There is no movement of electrons.
They have more conductivity and less resistivity.	They have more resistivity and less conductivity.

Uses of Conductors

1. Electrical conductors carry electric current. The wires are made of copper or aluminium.
2. Tungsten is a metallic conductor that has high resistance to create heat and light in incandescent lamps.
3. The windings (bundle of wires) of motors, generators and transformers are made of copper to carry maximum current.

Uses of Insulators

1. The current-carrying conductors are covered with an insulator such as plastic.
2. Transformer windings are kept in a tank of oil for cooling. Oil is an electrical insulator.
3. The outer cover of many electrical machines is made of insulators to prevent the current from giving a shock to the people handling it.
4. People repairing electrical equipment wear rubber boots and gloves. People also stand on dry wooden furniture while touching wires.
5. Glass or ceramic insulators are used to hold or support high voltage power lines.

Conductors and Insulators – Solved Example

Q.1. A cubical block of wood is \(1\,\rm{m}\) long. Wood has a resistivity of \(10^{14}\,\rm{Ωm}\). What is its resistance?
Ans: Given,
\(l = 1\,\rm{m}\)
\(A = 1\,\rm{m}^2\)
\(ρ =10^{14}\,\rm{Ωm}\)
Resistance equation is,
\(R = \frac{{\rho l}}{A}\)
\(R = \frac{{{{10}^{14}} \times 1}}{1} = {10^{14}}\,{\Omega }\)
We can see that wood has a very high resistance and makes an excellent insulator.

Summary

In this article, we have seen how we classify materials into conductors and insulators based on their electrical properties and on the way they allow or hinder electric current. The nature of the atoms a material is made up of first decides this property. We have seen how the dimensions and the type of material make something a conductor or opposer of electric current. This knowledge is important as we have to make machines that work using electricity and wires that carry it. It is also very important to know about the level of opposition offered by insulators to current to make safety equipment to protect people who work with electricity and use it daily. Large transmission lines carry electric power for thousands of kilometers. They have to be supported at regular distances by towers. High-quality insulators are designed and placed on these towers to hold the lines. Electrical energy is used at a very rate in the world, and expensive resources are needed to create and transmit it. Therefore, proper knowledge of the materials that handle it is essential.

Frequently Asked Questions (FAQs) on Conductors and Insulators

Q.1. Why is tungsten used to make filament in an incandescent bulb?
Ans: Tungsten is a metal having a very high melting point. It has comparatively more resistivity. By making it very thin and very long, its resistance can be increased to a high value, enough to create heat using the current and glow, giving out light.

Q.2. Why does an electrician wear rubber gloves when working on electrical lines?
Ans: Rubber is an insulator, and it prevents current from passing from the line to their body.

Q.3. Does the resistance of a material increase with a thicker conductor?
Ans: No. Resistance decreases with more thickness.

Q.4. What makes an insulator oppose current?
Ans: Insulators are materials that do not have electrons needed for current flow.

Q.5. What is the relationship between resistivity and conductivity?
Ans: Resistivity and conductivity are reciprocal to each other.