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

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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.

can someone help me with some logarithmic and exponential equations.
20/(×-6^2)
Salomon
okay, so you have 6 raised to the power of 2. what is that part of your answer
I don't understand what the A with approx sign and the boxed x mean
it think it's written 20/(X-6)^2 so it's 20 divided by X-6 squared
Salomon
I'm not sure why it wrote it the other way
Salomon
I got X =-6
Salomon
ok. so take the square root of both sides, now you have plus or minus the square root of 20= x-6
oops. ignore that.
so you not have an equal sign anywhere in the original equation?
Commplementary angles
hello
Sherica
im all ears I need to learn
Sherica
right! what he said ⤴⤴⤴
Tamia
what is a good calculator for all algebra; would a Casio fx 260 work with all algebra equations? please name the cheapest, thanks.
a perfect square v²+2v+_
kkk nice
algebra 2 Inequalities:If equation 2 = 0 it is an open set?
or infinite solutions?
Kim
The answer is neither. The function, 2 = 0 cannot exist. Hence, the function is undefined.
Al
y=10×
if |A| not equal to 0 and order of A is n prove that adj (adj A = |A|
rolling four fair dice and getting an even number an all four dice
Kristine 2*2*2=8
Differences Between Laspeyres and Paasche Indices
No. 7x -4y is simplified from 4x + (3y + 3x) -7y
is it 3×y ?
J, combine like terms 7x-4y
im not good at math so would this help me
yes
Asali
I'm not good at math so would you help me
Samantha
what is the problem that i will help you to self with?
Asali
how do you translate this in Algebraic Expressions
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
what's the easiest and fastest way to the synthesize AgNP?
China
Cied
types of nano material
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
what is nanomaterials​ and their applications of sensors.
what is nano technology
what is system testing?
preparation of nanomaterial
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
what is system testing
what is the application of nanotechnology?
Stotaw
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
can nanotechnology change the direction of the face of the world
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
how did you get the value of 2000N.What calculations are needed to arrive at it
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