# 0.19 Even semester2014-midsemester examination answers  (Page 3/3)

1. This velocity can be thermal velocity or Pauli Velocity.

Answers: Conducting electron is strongly scattering in metallic crystalline lattice but very wekly scattering in Semiconductor as exhibited by short Mean Free Path in metals and by long Mean Free Paths in Semi-conductors.[1/4+1/4=1/2]

XXV. In the Table given in Question XIV which is Pauli Velocity and which is Thermal Velocity?

Answers: Conducting Electron velocities in Metals are Pauli velocities because they arise out of Pauli-Exclusion Principle whereas conducting electron velocities in Semi-conductor are thermal velocities.[1/4+1/4=1/2]

XXVI. In Question XVIII, intrinsic Ge has the least resistivity and intrinsic GaAs has the maximum , Why? Answers; Ge has the least Band-Gap and GaAs has the widest Band-Gap.[1/4+1/4=1/2]

XXVII.

This is what statistics and does it tell. At T= 0 Kelvin what kind of distribution is it? Answers: This is Fermi-Dirac Statistics, P(E) gives the probability of occupancy of E by Fermions, and Absolute Zero the distribution is RECTANGULAR.[1/6+1/6+1/6=1/2 Points]

XXVIII.

What is this expression ? Define all the terms. Answers: N(E)→Density of States per unit energy, (E-E C ) →kinetic energy of conducting electron in conduction band.[1/4+1/4=1/2]

XXIX. If Ultra-Violet light of λ = 0.2μm is incident on a metal then which of the metals listed in the Table below will respond and emit electrons ? Answers;UV photon has 6.2eV hence it is powerful enough to cause photo-emission in all the Metals listed in the Table below.All the metals have a work-function less than 6.2eV.[1/2 Poiint]

Metal Work-function Metal Work-function
Na 2.3eV Ca 3.2eV
K 2.2eV Ba 2.5eV
Cs 1.8eV Pt 5.3eV
W 4.5eV Ta 4.2eV

XXX.

Answers: This expression tells how EXCESS CARRIERS decay with respect to time in Semiconductors with excess carrier life-time or excess carrier relaxation time defined as τ n . Excess carriers exponentially decay with time. If relaxation time is long then excess carriers transient takes a long time to decay.[1/2 points]

Question 2.Describe the step for preparing Electronic Grade Poly-crystal Silicon from sand.

[7.5 marks]

Reduction of sand with carbon gives impure polycrystalline Silicon

Reaction of pulverized raw silicon with HCl gaseous vapour to form TriChloroSilane

Multiple distillation of TriChloroSilane to obtain purified electronic grade TriChloroSilane

Thermal decomposition of SiHCl3 at 1000 degree centigrade in Sieman’s reactor to obtain fattened rods of electronic grade Silicon

Question 3. Balmer Series Spectral Lines from Stars are determined to be at 6563A°,4862A°,4341A°,4102A° and 3970A°. Determine these spectral lines theoretically.

[By the Red-Shift of these Balmer Spectral Lines the velocity of the receding Galaxy is detyermined. The recession velocity gives the distance of the Galaxy using Hubble’s relationship][7.5 marks]

Answer: λ(μm)=1.24/E g (eV) here E g = (13.6eV/4-13.6/n^ 2 )eV. Since the answer is to be obtained in Angstrom therefore the final expression is:

Therefore λ(Angstrom)=( (1.24/(13.6/4-13.6/n^ 2 ))×10^ 4 )Angstrom.

For n=3 to n=2, λ=6564.71A°;

For n=5 to n=2, λ=4862.75A°;

For n=6 to n=2, λ=4341.74A°;

For n=7 to n=2, λ=4102.94A°;

For n=8 to n=2, λ=3971.24A°;

Question 4.Detrmine the temperature at which E=E F +kT will be occupied by electron with P(E)=1%.[7.5 marks]

This question is wrongly stated. At E=E F +kT the Probability of occupancy is 1/(1+e) =0.2689. It can be never 1% irrespective of temperature.

The correct question is: Determine P(E F + kT) in Fermi-Dirac Statistics. Determine Temperature T at which P(E F + 0.5eV) = 1%.[Answers: 0.27, 1262Kelvin]

You can give either of the answers and fetch full marks.

what is the stm
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
what is Nano technology ?
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
why we need to study biomolecules, molecular biology in nanotechnology?
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
why?
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
what does nano mean?
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
it is a goid question and i want to know the answer as well
Maciej
Abigail
for teaching engĺish at school how nano technology help us
Anassong
How can I make nanorobot?
Lily
Do somebody tell me a best nano engineering book for beginners?
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
how can I make nanorobot?
Lily
what is fullerene does it is used to make bukky balls
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
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