Question

State the order of resistivity of (i) a metal, (ii) a semiconductor and (ii) an insulator.
(A). Semiconductor > metal > insulator
(B). Metal > semiconductor > insulator
(C). Insulator > semiconductor > metal
(D). Insulator > metal > semiconductor

Answer 1

Hint: Resistivity of a material is the ability to oppose the flow of charge through it when a potential difference is established across the material. It depends whether the electrons are free to move. Metals have free moving electrons whereas insulators have electrons under strong electromagnetic force from the nucleus. Semiconductors fall in between these two.

Complete step by step answer:
Resistivity of a material is the ability to oppose the flow of charge through it when a potential difference is established across the material. It is a material property. It depends on the interior structure or atomic arrangement within the material.
Materials are categorised in terms of their conductivity. Conductivity is the opposite action of resistivity. It is the ability of a material to allow the charges to flow through it when a potential difference is established across it. Simply to say, conductivity is the reciprocal of resistivity. The material with high resistivity has low conductivity and a material with low resistivity has high conductivity.
The materials which have high conductivity and low resistivity are called good conductors. Most of the good conductors are metals. Metals have a large charge density of free moving electrons. When a potential difference is applied across them, the electric force easily affects the free electrons and the charges flow without much restriction. Hence, metal easily conducts electricity.
The materials which have very low or zero conductivity are called insulators. These materials have very high resistivity. The charges (electrons) in these materials are not free like in metals and are bonded to atoms or molecules with strong forces. Therefore, when a potential difference is applied across the material, the electrons do not flow easily and need very high energy to make the electrons to flow through the material.
The intermediate materials are called semiconductors. They have conductivity and resistivity values between good conductors (metals) and insulators. The flow of charges in semiconductors is due to shifting or jumping of electrons from an excess place to a vacant place.
Therefore, from the above statements the order of resistivity of a metal, a semiconductor and an insulator is as follows :

Insulator > semiconductor > metal

Note: Change in temperature of a material affects the resistivity of the material. The effect of change in temperature is different for good conductors and semiconductors.
In good conductors, as the temperature is increased the resistivity of the material increases.
In semiconductors, as the temperature is increased the resistivity of the material decreases.