Tuesday 15 April 2014
Saturday 8 February 2014
Q.No.223: - Explain how to generate the forward bias portion of the characteristic curve.
Q.No.223: - Explain how to
generate the forward bias portion of the characteristic curve.
Ans: - The forward voltage (VF) increases to
the right along the horizontal axis, and the forward current (IF) increases
upward along the vertical axis. Q.No.222: - Describe the motion of electron and holes in a semiconductor.
Q.No.222: - Describe the
motion of electron and holes in a semiconductor.
Ans: - In a semiconductor the
current flows due to the motion of electrons and shifting of holes. The
electrons occupy the place of holes and made a hole in their own place and the
upcoming electron take the place of that hole and so on. So in semiconductors
the current due to electrons flow in one direction and the current due to
shifting of holes flow in other direction.
Q.No.221: - Describe what is the effect of barrier potential during forward biasing and reverse biasing.
Q.No.221: - Describe what is
the effect of barrier potential during forward biasing and reverse biasing.
Ans: - Potential barrier is also
called depletion region. When the diode is forward biased then the size of
depletion region decreases and when the diode is reverse biased then the
depletion region become wider.
Q.No.220: - Describe the V-I characteristics for reverse biasing a diode in practical model using graph.
Q.No.220: - Describe the
V-I characteristics for reverse biasing a diode in practical model using graph.
Ans: - When the diode is reverse
biased, it is equivalent to an open switch just as in the ideal model. The
barrier potential does not affect reverse bias, so it is not a factor.
Q.No.219: - Distinguish between conductors insulators and semi conductors on the basis of energy band theory also draw diagrams.
Q.No.219: - Distinguish
between conductors insulators and semi conductors on the basis of energy band
theory also draw diagrams.
Ans: - According to the energy
band theory the insulators are those materials in which there is a large energy
difference between valence and conduction band. The conduction band is empty,
and the electrons in the valence band acquire a large amount of energy to jump
in conduction band and become free. The forbidden gap is very large between
valence and conduction band. That’s why the insulators did not conduct. The
electric current is defined as the flow charge and there are no free electrons
or holes in insulators so no current flows.
Conductors are those materials in
which there is no difference of energy between valence and conduction band, or
these two bands are overlapped. Electrons can easily jump from valence and
conduction band. In conductors the conduction band is partially filled than
those of insulators. As there are electrons is conduction band so such
materials are good conductors of electricity. There is no forbidden gap between
valence and conduction band in conductors.
Semiconductors
are
those materials in which there is a very small energy difference between
valence and conduction bands and electrons and can easily jump by acquiring a
small amount of energy. In semiconductors the there is a very small forbidden
gap between valence and conduction bands.
Wednesday 5 February 2014
Q.No.218: - Discuss the diffusion across a pn junction.
Q.No.218: - Discuss the
diffusion across a pn junction.
Ans: - The free electrons in the
n-region are attracted toward the p-region of diode they are attracted toward
the p-region due to majority of positive charge and diffuse across the junction
into the p-region where they combine with holes.
Q.No.217: - Describe a diode and how a pn junction is formed?
Q.No.217: - Describe a
diode and how a pn junction is formed?
Ans: - If a piece of intrinsic
semiconductor silicon is doped so that one part is n-type and the other is
p-type, a pn junction forms at the boundary between the two regions and a diode
is created. The p-region has many holes (majority carriers) from the impurity atom and very small quantity
of thermally generated free electrons (minority carriers). The n-region has
electrons as majority charge carriers which come from impurity atoms and very
small quantity of holes which are created due to break known of bonds.
Q.No.216: - What are the p-type and n-type semi-conductors?
Q.No.216: - What are the
p-type and n-type semi-conductors?
Ans: - The intrinsic
semi-conductors which are doped with pentavalent impurity atom becomes an
n-type semiconductor because of majority of electrons and the intrinsic
semiconductors which are doped with trivalent impurity atom becomes a p-type
semiconductor because of the majority of positively charged holes.
Q.No.215: - What is the process of doping?
Q.No.215: - What is the
process of doping?
Ans: - Addition of impurity in
intrinsic (pure) semi-conductor is called doping.
Q.No.214: - Why germanium is more unstable at high temperature and why silicon is widely used than germanium?
Q.No.214: - Why germanium
is more unstable at high temperature and why silicon is widely used than
germanium?
Ans: - The valence electrons in
germanium are in the fourth shell while those in silicon are in the third
shell, closer to the nucleus. This means that the germanium valence electrons
are at high energy levels than those in silicon and therefore, require a
smaller amount of additional energy to escape from the atom. This property
makes germanium more unstable at high temperatures and results in excessive
reverse current. This is why silicon is a more widely used semi-conductive
material.
Q.No.213: - What is conduction band also define energy gap.
Q.No.213: - What is
conduction band also define energy gap.
Ans: - Conduction band:
- When an
electron acquires enough additional energy, it can leave the valence shell,
become a free electron, and exist in what is known as the conduction band.
Energy gap: - The
difference in energy between the valence band and the conduction band is called
an energy gap.
Q.No.212: - What are the types of semiconductors?
Q.No.212: - What are the
types of semiconductors?
Ans: - There are two types of
semiconductors
(i)
Intrinsic
semiconductors
(ii)
Extrinsic
semiconductors
Q.No.211: - Define semiconductors. Also give its examples.
Q.No.211: - Define
semiconductors. Also give its examples.
Ans: - A semiconductor is a material
that is between conductors and insulators. In its ability to conduct electrical
current. Its examples are silicon, germanium and carbon.
Q.No.210: - Why electric current pass through conductors?
Q.No.210: - Why electric
current pass through conductors?
Ans: - Because conductors have
electrons that are loosely packed with nucleus and become a free electron after
getting a small energy. These free electrons conduct electricity.
Q.No.209: - Define conductors.
Q.No.209: - Define
conductors.
Ans: - A conductor is a material
that easily conducts electrical current. Most metals are good conductors. The
best conductors are single element materials such as copper, silver and gold
etc.
Monday 3 February 2014
Q.No. 208: - Why electric current does not conduct through insulators under normal conditions?
Q.No. 208: - Why electric
current does not conduct through insulators under normal conditions?
Ans: - Because in insulators
electrons orbiting around the nucleus are tightly bound. The free electrons in
the insulator are very rare, so that’s why the electric current did not pass
through the insulators.
Q.No.207: - Define electric current.
Q.No.207: - Define electric
current.
Ans: - Flow of electric charge
from high to low potential is called electric current
I =
Q/t
Where
I represents current, Q for charge and t for time.
Q.No.206: - Define insulator.
Q.No.206: - Define
insulator.
Ans: - An insulator is a material
that does not conduct electrical current under normal conditions. Most good
insulators are compounds rather than single element materials
Q.No.205: - When an atom becomes a positive ion and when it becomes a negative ion?
Q.No.205: - When an atom
becomes a positive ion and when it becomes a negative ion?
Ans: - When an atom loses an
electron then it becomes a positive ion and when an atom accepts an electron
then it becomes a negative ion.
Q.No.204: - How ionization takes place?
Q.No.204: - How ionization
takes place?
Ans: - Ionization takes place by
providing sufficient amount of energy to the atom. The electrons become excited
and get more energy. When the energy of valence electron overcome the
electrostatic force between nucleus and that electron then electron detach from
nucleus and atom become a positive ion.
Q.No.203: - Define ionization.
Q.No.203: - Define
ionization.
Ans: - The process of losing electron from valence
shell is known as ionizationQ.No.202: - How the energy vary in different shell of atom.
Q.No.202: - How the energy
vary in different shell of atom.
Ans: - Electron that are away
from nucleus have higher energy while the electrons nearer the nucleus have low
energy.
If
the orbit with n=1 have energy E1
If
the orbit with n=2 have energy E2
If
the orbit with n=2 have energy E3
If
the orbit with n=2 have energy E4
If
the orbit with n=2 have energy En-1
If
the orbit with n=2 have energy En
Then,
E1<E2<E3<E4<En-1 <En
Q.No.201: - Define valence shell.
Q.No.201: - Define valence
shell.
Ans: - The outermost shell of an
atom is called valence shell. It may be partially or completely filled with
electrons, but it cannot be empty at all.