This article describes the properties of electrical conductor, such as conductivity, resistivity, thermal conductivity, malleability, ductility, and reflectivity. An electrical conductor is a path or a bus through which electrical charges flow from one point to another to do some work. Electrical charges have attractive repulsive forces between them, depending on their respective nature.
To get work done i.e., to convert the electrical energy into another form of energy like heat energy or mechanical energy, these charges with their net electrical force are required to be moved from one point to another as work done by a physical entity is the product of the applied force and its displacement. An electrical conductor provides for the movement of the charges from one point to the other.
An electrical conductor is made from a good conducting material like copper, nichrome, aluminum, etc. depending on the nature of the application. There are various factors depending on which electrical conductor is selected.
Apart from conductors, there are semi-conductors and non-conductors or insulators. Semiconductors are used in applications where high-frequency switching of the state of the device with respect to time is required. These devices work as a conductor and non-conductor depending on the requirement.
A non-conducting material is one which can’t conduct electricity freely under a normal range of voltage not exceeding its breakdown voltage. These materials are also called insulators as these are used to cover conductors for their safe handling. An insulator being non-conductive helps in avoiding the flow of charge between two conducting bodies or between a conductor and the earth.
The flow of a charge through a conductor per unit of time is known as electric current. In other words, the number of charged particles flowing through a conductor in 1 second is known as the electric current through the conductor. According to Ohm’s law, this electric current is directly proportional to the potential difference across the conductor. Current flows in the direction of lower potential from higher potential.
Where V is the potential difference across a given conductor, i is the current passing through it which is equal to the rate of flow of charges (q) per unit time (t). R is the constant of proportionality known as the Resistance of the conductor.
Now as we have discussed in detail about a conductor, let’s look at the various properties of a conductor based on which we can select a conductor for our own applications.
Properties of Conductor
We will discuss the following properties of electrical conductors.
- Availability of free electrons
- Thermal conductivity
- Electric Field Inside Conductor zero
Now, we will discuss each property of the conductor in detail.
1. Conductivity– Property of conductor
The conductivity of a conductor is one of the most important factors when comparing two or more conductors based on their efficiency. As the name suggests, conductivity is the measurement of the ease of flow of electric current through a conductor for a given potential difference. It is the conductivity of a material that allows us to differentiate between a conductor, a semiconductor, and an insulator. All metals like Copper, Aluminum, Silver, etc. are good conductors of electricity. Copper and Aluminum are extensively used in various electrical machines and appliances as these are cheaper than other metals and have great conductivity.
Conductivity is denoted by σ and it is the reciprocal of resistivity. Conductivity is given by
Where R is the resistance of the given conductor, l is the length of the conductor and A is the area of the cross-section of the conductor. It can also be represented as
Where S=1/R and S are known as conductance. The unit of conductance is Siemens.
Thus, conductivity is the property of a conductor that allows the conductor to easily pass an electric current through it.
Resistivity is the reciprocal of conductivity. It is the measurement of hindrance in the flow of electric current through a conductor. Therefore, it goes without saying that a good conductor must have low resistivity. The resistivity of a conductor is given as
Where R, l, A is the resistance, length, and the area of cross-section of the conductor.
Contrary to conductivity, resistivity is the property of a conductor that resists the flow of electric current through it.
3. Availability of Free Electrons
The presence of free electrons is important property of conductor that allows the conduction of electric current through a material. All metals have free electrons in their outer shell which makes them a good conductor of electricity. The electrons in the outer shell of these metal atoms are held loosely to the nucleus and in the presence of an electric field (due to a potential difference), these electrons come off their respective shells.
As a result, a pool of free electrons is created which flows all through the metal body. These electrons carry a negative charge and thus their flow causes the conduction of electric current.
Unlike metals, non-conductors or insulators have no free electrons in their outer shell. Therefore a strong electric field is required to rip off the electrons in order to start conduction. Such electric field intensity can be achieved at a very high voltage which is known as the breakdown voltage.
Thus, these non-conductors can be safely used as insulating material until the system voltage reaches the breakdown voltage.
For example, the breakdown strength of air is 30kV/cm which means electricity can conduct through a 1 cm gap between two points separated by air if the potential difference between the gap reaches 30kV or more. Until this voltage, the two points at a gap of 1 cm are safely insulated through the air.
4. Thermal Conductivity– Property of conductor
Thermal conductivity property is equally important for a conductor as the electrical conductivity. Certain electrical machines or appliances have to run constantly and the flow of current through them causes the generation of heat due to their intrinsic resistance. This heat is a loss of input power that can’t be done away with.
Therefore, the conducting material must be able to handle the increase in its temperature and hence the melting point must be high. Copper and Aluminum have higher thermal conductivity and hence these are used in heavy-duty machines.
The heat generated in a conductor is given by
Where i is the current through the conductor, R is the resistance of the conductor and t is the time for which the current flows.
It is clear from the equation that to reduce the heat loss through the conductor either the current i or the resistance R or the time of operation t must be reduced. In a practical scenario, i and t can’t be reduced beyond a limit and therefore the resistance of the conductor in use must be low so that it can handle the generated heat efficiently.
Many conductors, such as copper and aluminum, are highly ductile, which means they can be drawn into thin wires without breaking. This property of conductor is crucial for the production of electrical wires and cables.
6. Malleability– Property of Conductor
A conducting material must be malleable in nature, allowing it to be easily shaped or formed into different configurations. This property is beneficial for various applications, such as creating conductive tracks on circuit boards.
Inductance is the tendency of an electrical conductor to oppose a change in the electric current flowing through it. Therefore, for a conductor carrying direct current, Inductance is not a problem as the time-rate change of current is zero in the case of DC. But most of the practical appliances and machines operate on AC voltage and hence inductance provided by a conductor is of extreme importance.
According to the laws of electromagnetic induction, a time-varying current passing through a conductor causes the generation of magnetic field flux within and outside the conductor. The magnetic field outside the conductor is extremely low compared to inside the conductor. This magnetic field causes an emf to be induced within the conductor which is in opposition to the applied voltage across the conductor. The induced emf is given as;
Where E is the induced emf, L is the inductance of the conductor and di/dt denotes the time-rate change of current through the conductor. The minus (-) symbol indicates that the induced emf is in opposition to the applied potential difference across the conductor.
This causes a reduction in the current flowing through the conductor and therefore the current seeks an alternative path where the effect of this magnetic field is low that is outside the conductor. This is known as the skin effect. Skin-effect causes wastage of the cross-sectional area of the conductor as the current tends to flow through the outer surface of the conductor instead of flowing through the core of the conductor.
As evident from the above equation, the inductance (L) of a good conductor must be low to avoid a problem like skin-effect.
8. Electric field inside a conductor is zero
A conductor has no electric field intensity of itself. This allows the free movement of electrons within the conductor. Had there been any electric field within the conductor, the electrons would have aligned in a direction opposite to the direction of the field thus creating a pool of negatively and positively charged particles separated within the conductor. But the electrons freely move throughout the conductor until impressed by an external electric field.
The electromagnetic waves. including light, when falls on the surface of a good conductor, gets reflected. Silver and copper is a good conductor of electricity and they have free electrons bound to their atoms. When electromagnetic waves fall on such conductors, the free electrons can move easily.
An oscillating electric current sets up in the conductor because of the back-and-forth movement of electrons, and this oscillating current generates electromagnetic waves. These waves are called the reflected wave.
High conductivity, low resistivity, and free electron mobility are the properties of the conductor that make them suitable for electrical applications that cause efficient flow of electric current.
This is all about the Properties of Electrical Conductors.