Electrical Conductivity
Electrical conductivity is a physical property of materials that represents a material’s ability to conduct electric current. The SI unit of electrical conductivity is siemens per meter (S/m).
The electrical conductivity of a material is determined by several factors, including the density and mobility of charge carriers (such as electrons or ions), the structure of the material, temperature, and other environmental factors.
Materials with high electrical conductivity, such as metals and some types of salts and solutions, are commonly used in electrical and electronic applications, where they are used to carry electric current with minimal resistance or loss of energy. Other materials with low electrical conductivity, such as insulators and semiconductors, are used in applications where they can be used to control or manipulate the flow of electric charge.
Free Electrons and Electrical Conductivity
Free electrons are electrons that are not bound to an atom or molecule and are free to move through a material. Electrical conductivity is a measure of a material’s ability to conduct an electric current. The conductivity of a material is dependent on the number of free electrons that are available to carry the electric charge.
Materials that have a high number of free electrons, such as metals, are good conductors of electricity. In metals, the valence electrons of the atoms are loosely bound to the atomic nucleus, allowing them to move freely through the material. This makes metals good conductors of electricity.
In contrast, materials that have few free electrons, such as nonmetals, are poor conductors of electricity. Nonmetals tend to have tightly bound electrons that are not free to move through the material, so they do not conduct electricity well.
Overall, the presence of free electrons is a critical factor in determining the electrical conductivity of a material.
Electrical conductivity can be defined as how much voltage is required to get an amount of electric current to flow. This is largely determined by the number of electrons in the outermost shell; these electrons determine the ease with which mobile electrons are generated. Another factor is the number of atoms per unit volume, which determines the number of electrons that will readily move in response to an electric field. Materials that have high electrical conductivity are typically metals and alloys, as well as some types of salts and solutions. This is because these materials have a large number of free electrons that are not bound to individual atoms and are able to move freely through the material.
Metals such as copper, aluminum, silver, and gold are well-known for their high electrical conductivity and are commonly used in electrical and electronic applications. Other metals and alloys with high electrical conductivity include tungsten, platinum, and brass.
Some types of salts and solutions also have high electrical conductivity due to the presence of free ions that can carry an electric charge. For example, solutions of sodium chloride (table salt) or other salts can conduct electricity well, as can some types of acids and bases.
How do electrons flow in a wire?
When a voltage is applied across a conductor, an electric field is established, which causes the electrons to move in a certain direction. However, the electrons do not move in a straight line but rather undergo a random motion due to collisions with the atoms of the conductor, losing energy and scattering in random directions. This creates resistance to the flow of electrons and causes some of the energy of the electric field to be converted into heat.
This random motion causes the electrons to have an average velocity, which is called the drift velocity.
The drift velocity of electrons in a conductor is typically quite slow, on the order of a few millimeters per second, even though the current in the conductor may be quite high. This is because the electrons are constantly colliding with the atoms of the conductor, which slows down their overall motion. Drift velocity is proportional to current. In a resistive material, it is also proportional to the magnitude of an external electric field.
While the drift velocity is relatively slow, it is still an important concept in understanding the behavior of electric currents in conductors. The overall flow of electric charge in a conductor is determined by the combination of the drift velocity and the number of charge carriers moving through the conductor.
For example, when a DC voltage is applied, the electron drift velocity will increase in speed proportionally to the strength of the electric field. The drift velocity in a 2 mm diameter copper wire in 1 ampere current is approximately 8 cm per hour. AC voltages cause no net movement; the electrons oscillate back and forth in response to the alternating electric field (over a distance of a few micrometers).
