Valance electrons or
band
- The electrons in the outer most orbit of
an atom are called as valance electrons.
- The valance electrons have highest
energy.
- This band may be partially or completely filled.
- The partially filled band can accommodate more number
of electrons.
Conduction band
- It is band of electrons which are responsible
for conduction of current in the conductor.
- All the electrons in the conduction band
are free.
- The conduction of current through
material is not possible if the conduction band is empty.
- The insulators have empty conduction band
where it is partially filled for conductors.
Forbidden energy band
- It is gap between conduction band and
valance band on the energy level diagram.
- The width of forbidden energy gap
indicates bondage of valance electrons to its atom.
- Less the forbidden energy gap, less tightly valance electrons are bound to electrons and vice versa.
Classification of
material on the bases of energy bands
- The electrons of the lower or last orbit
are closely bound with nucleus there are they does not play
important role in the conduction process.
- The valance band and conduction band
plays important role to decide electrical behavior of the material.
Conductor
- It is substance or material in which
electrical current easily passes through it i.e. copper and aluminum.
- The valance band and conduction band
overlap each other which create small potential difference.
- This potential difference causes flow of
electrons which constitute electrical current.
- The energy band diagram is shown in the figure A.
Semi conductor
- It
is substance or material in which small electrical current easily passes
through it i.e. silicon, germanium.
- The
conductivity of semi conductor lies between insulator and conductor.
- The
valance electron is completely filled whereas the conduction band is
almost empty as shown in the figure B.
- However
the energy gap ( forbidden gap ) between valance band and conduction band
is very small ( 1 eV ).
- The
electrical current allows to flow if small electric field applied across
it.
- The
semiconductor behaves as an insulator at room temperature or low
temperature.
- However
some electrons cross conduction band causes small electric current even at
room temperature.
- As
the temperature increases, more electrons pass through valance band to
conduction band resulting conductivity increases.
- The
semiconductor has negative temperature co – efficient of resistance
because as the temperature increases electrical conductivity of semi
conductor increases or resistance decreases.
- Finally
we can say that the semi conductor material has
Empty conduction band
Full valance band
Small forbidden energy gap between valance band and conduction band
Insulator
- It
is a substance or material in which electric current does not pass through
it i.e. wood, glass, plastic etc.
- The
valance band is full whereas the conduction band is empty as shown in the
energy band diagram.
- The
forbidden energy gap between valance band and conduction band is large (
15 eV ).
- The
electrons of the valance band require very high electric field in order to
cross it and move in the conduction band.
- The
electrons of the valance band do not have enough energy to cross and move
towards conduction band therefore the conductivity of the insulator is
almost zero.
- The resistance of the insulator decreases with increase in the temperature therefore it has negative temperature co – efficient.
You may also like :
Professionally written blogs are rare to find, however I appreciate all the points mentioned here. I also want to include some other writing skills which everyone must aware of.
ReplyDeleteกล่อง รองเท้า
How is solar power created? To create solar power, you'll need a solar panel, which is made out of at least one solar cells. Zonnepanelen
ReplyDeleteExtremely intriguing online journal. A lot of web journals I see nowadays don't generally give anything that I'm keen on, however I'm most definitely inspired by this one. Recently felt that I would post and let you know. energia fotovoltaica castellon
ReplyDeleteEmployments like upkeep and establishment don't require a long haul preparing and are along these lines progressively favorable for the individuals who don't have numerous aptitudes and are jobless. Zonnepanelen installateur
ReplyDelete