The relation between the temperature and conductivity in insulators and conductors
Conductivity is the ability of a substance to conduct electrical current. This is determined by free electrons available in the material. The distance between the free electrons and the nucleus determines the extent of electrical current conductivity. Insulators, for example carbon, have all their electrons used in bonding. Thus, the valence band is completely filled. Also, the gap between the valence band and the conduction band is too large for many electrons to make it to the conduction site to enable electrical energy flow. For electrical energy to be transmitted, the carriers have to cross over to the conduction band. This is made impossible by the large distance between covalent band and conduction band. Therefore, they are not capable of transmitting electrical current. Their coefficient of conductivity is too low to transfer electrical current from one point to another. Thus, the electrical conductivity of insulators is nil. Unless the temperature is high enough to enable the carriers to hop from valence band to conductivity band, insulators do not conduct electrical current.
Conductors are materials that can easily allow electrical current flow from one point to another. The atoms in metals, for example iron, are closely packed together. As a result, the electrons from one atom experience great attraction to the adjacent atom. Thus, the distance between covalent band and the conduction band becomes small to allow energy transfer. By receiving a small amount of energy from an external source, the electrons ascend to higher energy levels. These electrons are responsible for conductivity in conductors such as metals. The density of free electrons in good conductors is higher in conduction band allowing fast conductivity. Electrons migrate to a higher terminal when a source of heat is connected. The movement allows the higher conductivity.
Conductors have different levels of conductivity varies depending on the number of free electrons. Those with many free electrons are best conductors while those with less free electrons are not very good conductors. Temperature and conductivity of conductors are directly proportional as long as the condition of the other part of the conductor remains the same. This means as the temperature increases the rate of conductivity also increases. But if the other conditions which include temperature, cross sectional area, length of the conductor varies, then the relationship between temperature and conductivity varies. Conductivity and cross sectional area of a conductor vary proportionally. On the other hand, length and temperature of the conductor are inversely related. This means that as the length increases, the conductivity reduces. Thus, the part that is close to the supply will be too hot while the part away from the external source will not be hot.