Question

The energy band gap is maximum in which of the following?
(A) Metals
(B) Superconductors
(C) Insulators
(D) Semiconductors

Answer 1

Hint:First we are going to understand what is the energy band gap and how it occurs.After that we are going to understand the properties of metals,semiconductors,
insulators and superconductors based on the energy band gaps.

Complete step by step answer:
Energy band gap: It is the energy difference between conduction band and valence band. In conduction band electrons present are free to move. Electrons present in valence bands are not able to move freely.
Energy Band Gap = Energy of Conduction Band - Energy of Valence Band.
Generally energy band gaps are expressed in eV (electron volts).
a) For metals Conduction Band and Valence Band overlap. So Energy band gap is very less. This means that electrons can easily cross the valence band into the conduction band. This makes electrons more easily available for conduction in metals. Making metals good conductors of electricity.
b) For Insulators there are no electrons present in the conduction band. Due to this there will be a large gap present between the conduction band and the valence band. It is very difficult to send electrons from the Valence band to the conduction band. So the energy band gap is very high. This makes insulators poor conductors of electricity. This means that insulators will have more energy gaps than energy gaps present in metals.
c) For Semiconductors energy band gap is moderate and lies between metals and insulators, since there are some conduction electrons present in the conduction band. This means that there are electrons present in the conduction band, but they are less than the electrons present in the metals. The electrons present in the conduction band of semiconductors are less than the electrons present in the insulators. Therefore this means that the energy gap present in the semiconductors are less than insulators but greater than metals.
d) For Superconductors energy band gap is less than metals, semiconductors, and insulators. This means that the electrons are readily available for conduction in superconductors.
Therefore, by comparing the energy gaps of all the four insulators have a maximum energy band gap.
Therefore Option (C) is the correct answer.

Note: In solid state physics band gaps are defined as a range of energy levels within a given crystal that are impossible for an electron to possess. Generally, a material may possess different levels of band gaps throughout its band structure. Based on the energy level band gaps, materials are classified into conductor,superconductors and insulators.The phenomenon of the band gap occurs when two adjacent allowed bands are not wide enough to span the full range of electron energy levels, hence this causes ‘gaps’ between the bands of different energy levels