Electrical Conductivity

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.

Electrical conductivity is closely related to resistivity (which is more commonly used):

σ=1/ρ

where σ is the conductivity (in m/Ohm), and ρ is the resistivity (in Ohm/m). To determine the resistance of a wire (which could be made of almost anything: copper, aluminum), use:

R=ρAl=Aσl

where A is the cross-sectional area of the wire (in m²) and l  is its length (in meters).

Electrical conductivity is closely related to electrical conductance. Electrical conductivity is a property of the material itself (like silver), while electrical conductance is a property of a particular electrical component (like a particular wire).

Electrical Conductivity and Materials

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.

Classification of Materials according to Electrical Conductivity

Materials can be classified into different categories based on their electrical conductivity. Here are some common categories:

1. Conductors: Materials with high electrical conductivity, such as metals and some types of solutions, are known as conductors. They are able to carry an electric current with minimal resistance and are commonly used in electrical and electronic applications.
2. Insulators: Materials with low electrical conductivity, such as plastics, rubber, and glass, are known as insulators. They are not able to carry an electric current easily and are commonly used to isolate and protect electrical components.
3. Semiconductors: Materials that have intermediate levels of electrical conductivity, such as silicon and germanium, are known as semiconductors. They can be used to control and manipulate the flow of electric charge and are used extensively in electronics and computer applications.
4. Superconductors: Materials that have zero electrical resistance at very low temperatures are known as superconductors. They are able to carry electric current without any loss of energy and are used in specialized applications such as MRI machines and particle accelerators.
5. Ionic conductors: Materials that conduct electricity through the movement of ions rather than electrons, such as some types of salts and electrolytes, are known as ionic conductors. They are commonly used in batteries, fuel cells, and other electrochemical devices.

Generally, most metals have high conductivity (which is another way of saying metals tend to be conductors) because the electrons in their outermost shell can move easily. Non-metals tend to have low conductivity.

Materials with the highest electrical conductivity

Here are seven materials with the highest electrical conductivity:

1. Silver – Silver has the highest electrical conductivity of all metals and is widely used in electrical and electronic applications due to its low resistance and high thermal conductivity.
2. Copper – Copper is the second-most conductive metal after silver and is commonly used in electrical wiring and electronic components.
3. Gold – Gold is a good conductor of electricity and is commonly used in electronic connectors, switches, and other components due to its corrosion resistance and low reactivity.
4. Aluminum – Aluminum is a lightweight metal with good electrical conductivity and is used in a variety of electrical applications, such as power transmission and distribution.
5. Tungsten – Tungsten has a high melting point and is a good conductor of electricity, making it useful in high-temperature electrical applications such as incandescent light bulbs and vacuum tubes.
6. Platinum – Platinum is a dense, corrosion-resistant metal with high electrical conductivity and is used in a variety of electrical and electronic applications.
7. Brass – Brass is an alloy of copper and zinc that has good electrical conductivity and is commonly used in electrical connectors, switches, and other components.

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).

Electrical and Thermal Conductivity

At a given temperature, the thermal and electrical conductivities of metals are proportional, but raising the temperature increases the thermal conductivity while decreasing the electrical conductivity. This behavior is quantified in the Wiedemann–Franz law. This law states that the ratio of the electronic contribution of the thermal conductivity (k) to the electrical conductivity (σ) of metal is proportional to the temperature (T).

Qualitatively, this relationship is based on the heat and electrical transport both involve the free electrons in the metal. The electrical conductivity decreases with particle velocity increases because the collisions divert the electrons from forwarding transport of charge. However, the thermal conductivity increases with the average particle velocity, increasing the forward transport of energy. The Wiedemann-Franz law is generally well obeyed at high temperatures. In the low and intermediate temperature regions, however, the law fails due to the inelastic scattering of the charge carriers.

It must be noted the general correlation between electrical and thermal conductance does not hold for other materials due to the increased importance of phonon carriers for heat in nonmetals.