Question

material on the basis of energy band

Answer 1

CONDUCTORS
In the metals like copper, aluminium there is no forbidden gap between valence band and
conduction band. The two bands overlap.
Hence even at room temperature, a large number of electrons are available for conduction.
So without any additional energy, such metals contain a large number of free electrons and hence called
good conductors.
INSULATORS
In case of such insulating material, there exists a large forbidden gap in between the conduction
band and the valence band.
Practically it is impossible for an electron to jump from the valence band to
the conduction band. Hence such materials cannot conduct and called insulators.
The forbidden gap is very wide, approximately of about 7 eV is present in insulators. For a
diamond, which is an insulator, the forbidden gap is about 6 eV.
Such materials may conduct only at very high temperatures or if they are subjected to high
voltage. Such conduction is rare and is called breakdown of an insulator.
The other insulating materials are glass, wood, mica, paper etc.
SEMICONDUCTORS
The forbidden gap in such materials is very narrow as shown in Fig. Such materials are called
semiconductors.
The forbidden gap is about 1 eV.
In such materials, the energy provided by the heat at room temperature is sufficient to lift the
electrons from the valence band to the conduction band.