Do you remember the structure of a copper atom we discussed in our previous article? We also saw what is the electric charge. We know that protons and neutrons are tightly bound into the nucleus while electrons orbit around it. Protons carry positive charge, electrons carry negative charge and neutrons are neutral. Atoms typically tend to be electrically neutral in their stable state. Therefore, number of electrons and number of protons is equal in a stable atom. An atom keeps protons and neutrons to itself, but it is able to share it’s outermost orbit electrons with neighboring atoms while forming molecules. Electrons in the outermost orbit (or outermost shell) are called as valence electron. On the basis of mobility of valence electrons, materials can be classified as – Conductors, Insulators and Semiconductors.
What is an electrical conductor?
An electrical conductor is a material that allows electricity (charges) to flow through it.
Basically, conductors are those materials in which electrons can easily move from one atom to another atom. Most metals are considered to be good conductors of electricity. In such materials, outermost electrons are loosely bound to the atoms. As many atoms combine to form solid metals, some valence electrons are liberated and can move with ease through the material. These liberated free electrons can move in the space between atoms by nothing more than the influence of room temperature.
Examples of conductors: Silver, copper, gold, aluminum, iron, steel, brass, bronze, mercury, graphite, impure water etc.
Copper and aluminum are most commonly used as conductors. Aluminum is not as good conductor as copper, but it is much lighter and cost-effective than copper. Therefore, aluminum conductors are widely used in power transmission and distribution systems. Copper wires are commonly used for domestic wiring. Silver is an even better conductor than copper, but is much expensive and, therefore, rarely used as a conductor.
What is an electrical insulator?
An electrical insulator is a material through which electricity or charges can not flow.
Insulators do not let electrons move very easily. In insulating materials, electrons are tightly bound to their atoms and cannot be freed without enough external pressure. Therefore, charges or electricity do not flow through insulators. Though insulators are not useful in transferring charges, they do serve a very important role in electronics and electrical systems. Insulators are used to restrict the unwanted flow of current. Most non-metals are insulators.
Examples of insulators: Glass, rubber, oil, asphalt, fiberglass, porcelain, ceramic, quartz, dry wood, plastic, PVC, diamond, pure water etc.
Electrical Conductivity and Resistivity
Not all metals are perfect conductors, neither all non-metals are perfect insulators. In fact, practically perfect conductors and perfect insulators are not present. It should be understood that not all conductors allow the same amount of charge flow. Also, not all insulators are equally to strong to restrict the charge flow.
Electrical resistivity is a fundamental property of a material that quantifies how strongly it opposes the flow of electric current. Materials with high resistivity strongly oppose the flow of electric current through them. Resistivity is commonly represented by Greek letter rho (ρ).
Electrical conductivity is a fundamental property of a material that quantifies material’s ability to flow the electric current. Materials with high conductivity allow more electric current to flow. Conductivity is commonly represented by Gree letter sigma (σ). Conductivity is the reciprocal of resistivity ( σ = 1/ρ).
What is a semiconductor?
A semiconductor is a material whose conductivity (or resistivity) lies between that of a conductor and an insulator. Although the atoms of a semiconductor have no free electrons, some valence electrons can be freed with a moderate electric force. Semiconductors can conduct electricity at a certain level without being damaged. Also, the conductivity of a semiconductor increases with increase in temperature.
Examples of semiconductors: Silicon (Si) and Germanium (Ge) are two most common examples of semiconductors.