(b.e. sem-1 g.t.u.) physics paper with solution
DESCRIPTION
These are physics's question papers with their solutions of GTU for course B.E. sem - 1TRANSCRIPT
GUJARAT TECHNOLOGICAL UNIVERSITY B.E. Sem-I Remedial examination March 2009
Subject code: 110011 Subject Name: Physics Date: 18 / 03 /2009 Time: 02:00pm To 4:30pm
Instructions: Total Marks: 70
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
Que-1 Attempt all the question. 14
1 Classify the sound waves based on frequency.
Based upon the frequency of sound waves it ca be define into three part
[a] Audible waves : 20 Hz to 20 KHz
[b] Infrasonic waves : below 20 Hz
[c] Ultrasonic waves : above 20 KHz
2 Define Reverberation time.
Reverberation time is defined as the time gap between initial direct note and reflected note at a
minimum audible level.
3 Define Ultrasonic waves.
The sound waves of frequency above 20kHz are called ultrasonic waves.
4 What is magnetostriction method?
Magnetostriction method is used to generate ultrasonic waves up to 3000 KHz using
magnetostriction effect.
5 What is SONAR?
The full form of Sound Navigation and Ranging. It is based on the principle of echo sounding.
6 What are lattice parameters?
There are six parameters : a, b, c, α β, γ.
7 What is LASER?
Light Amplification by stimulated emission of radiation. It is based on principle of echo sounding.
8 Define fiber optic system?
Fiber optic system is a communication system which uses optical fibers and light signal to carry
information signal.
9 What are conduction electrons?
The electrons in conduction band are called free or conduction electrons.
10 Classify the solids based in band theory.
Solids are classified into (1) conductor (2) semiconductor (3) Insulator.
11 What is holography?
Holography is techniques that allow the light scattered from an object to be recorded and later
reconstructed so that it appears as if the object is in same position relative to recording medium as
it was when recorded.
12 Define superconductor?
Superconductivity is defined as state of zero resistivity and perfect conduction of current through
it.
13 What are Nanomaterials?
A nanomaterial is made up by grains that are about 100 nm in diameter and contains less than a
few ten thousand of atoms.
14 Mention the names of the various NDT methods.
1 liquid penetrate-dye penetrate inspection
2 X-ray radiography
3 Ultrasonic inspection method
4 Magnetic particle inspection
5 Visual inspections.
6 Sonic inspections.
Que-2 (a)
1 The volume of room is 1500 m3.The wall area of the room is 260m2,
the floor area is 140m2 and the ceiling area is 140 m2 .The average sound
absorption coefficient for wall is 0.03, for the ceiling is 0.8 and for the
floor is 0.06. Calculate the average absorption coefficient and the
Reverberation time.
â = a1s1+a2s2+a3s3/s1+s2+s3
= (0.03*260)+(0.8*140)+(0.06*140)/260+140+140
= 0.2374 o.w.u.
Total sound absorption in room = â*s=∑ a.ds
= 0.2374*(260+140+140)
= 128.196 o.w.u. m2
Reverberation time T = 0.162V/ ∑ a.ds
= (0.162*1500)/128.196
= 1.95 sec.
3
2 Calculate the capacitance to produce ultrasonic waves of 106 Hz with an
Inductance of 1 Henry.
f = 1/2∏√LC
106 = 1/2*3.14*√1*C
C = 1/(2*3.14*106)2
= 0.0254*10-12
F
C = 0.0254 PF
2
3 Calculate the drift velocity of the free electrons in copper for an electrical
Field strength of 0.5 V/m (with a mobility of 3.5 ×10-3 m2 V- 1 S-1 ). n = 3.5 * 10
-3 m
2/vs
E = 0.5 v/m
V =nE = 3.5*10
-3*0.5
V = 1.75*10-3
m/s
2
(B)
1 Discuss the various factors affecting the acoustics of buildings and give their
Remedies Reverberation is one of the important factors that affect the acoustics of a building. Besides reverberation
there are other factors like loudness, focusing, echelon effect, extraneous noise and resonance.
Loudness:-
Suppose 1000 persons can hear the speech of a person in an auditorium, but there will not be any uniform
sound distribution. So to ensure uniform distribution of sound intensity in the hall electrically amplified
loudspeakers are used. These speakers are kept in different places in the auditorium and are kept at a higher
than the speaker’s head. Amplifiers shall make the low frequency tones more prominent and hence the
amplification has to be kept low.
Focusing The presence of cylindrical or spherical surface on the wall or the ceiling gives rise to undesirable focusing.
In hall, the observer receives sound waves from the speaker along the direct path and the observer also
receives the sound waves after reflection from the ceiling.
Echelon effect:- If there is regular structure similar to a flight of stairs or asset of railways in the hall, the sound produced in
front of such a structure may produce a musical note due to regular successive echoes of sound reaching the
observer. Such an effect is called echelon effect. If the frequency of this note is within the audible range, the
listeners will hear only this note prominently. To avoid echelon effect, the staircase must have to be covered
with carpets.
Extraneous noise:-
4
The extraneous noise may be due to the sound received form outside the auditorium and the sound produced
by fans inside the auditorium. The external sound cannot be completely eliminated but can be minimized by
using double or triple windows and doors. Proper attention must be given to maximum permissible speed of
time and the rate of air circulation in the room. The air conditioning pipes should be covered with corks and
insulated acoustically forms the main building.
Resonance:- The acoustics of a building may also be affected by resonance. So if the hall is of large size the resonance
frequency is much below the audible frequency limit and harmful effect due to resonance will not be
affected
Reverberation time: -
the auditorium must be designed in such a way that it could have the optimum reverberation time.
In an auditorium reverberation time can also be maintained by eliminating unwanted echoes, focusing
effects of curved surfaces, flatter echoes etc., Echoes, etc.
Sound absorption:- Sound absorption is a process in which sound energy is converted partly into heat and partly in to
mechanical vibrations of the material. Carpets, suspended space absorbers and interchangeable absorption
panels in rooms and buildings can absorb unwanted sound.
2 Using Sabine’s formula explains how the sound absorption coefficient of a material is determined?
Step 1:- - Using a source of sound inside the hall reverberation time is measured without inserting any test material.
let the reverberation time be T1
T1 = 0.161 V/A
= 0.161V/∑aS
1/T1 = ∑aS/0.161V………………………………………..(1)
Absorption coefficient = a
Effective absorbing area = aS
reverberation time = T
Step 2:- Now consider a material like curtain whose co-efficient of absorption is to be found out suspended inside
the room and reverberation time T2 is obtained.
1/T2 = ∑aS+2a2s2/0.161V……………………………………. (2)
Absorption coefficient of the material under investigation = a2
Effective absorbing area(since both the side are used it is multiplied by 2) = S2
So from equ. (1) and (2),
1/T2 -1/T1 =1/0.161V * 2a2s2
So 2a2s2 = 0.161V(1/T2 -1/T1)
a2 = 0.161V/2 s2*(1/T2 -1/T1) ……………………………..(3)
so equ. (1), (2), and (3) are known as coefficient of Absorption of an absorbing material which is suspended
in hall with both the surfaces open can be calculated.
3
OR
(B)
1 Draw the circuit diagram of piezoelectric oscillator and explain the
Production of ultrasonic waves using it. 4
Principle:- “when certain crystals like quartz, rochelsolt,tourmaline etc are stretched or compressed along
certain axis an electric potential difference is produced along a perpendicular axis ”
Construction:-
- A quartz crystal Q is placed between two metallic plates A and B and they are connected
with coil L3
- Coils L1, L2, L3 are inductively coupled to the oscillatory circuit of a triode valve.
- L2 connected with plate circuit
- L1 connected with variable capacitor c1 forming the tank circuit is connected between grid
and cathode.
- High tension battery is connected to L2 and cathode of a triode valve oscillator. Working:-
- when the switch S is closed and battery is switched on the oscillator produce high frequency
alternating voltage f = 1/2∏√L1C1
- The frequency of oscillation can be controlled bye variable capacitor C1.
- By transformer action an oscillatory emf is induced in coil L3.
- This emf are compressed on the plates A and B.
- Because of this emf crystal starts for vibration
- Adjust the variable capacitor c1 such that the frequency of a oscillation matches with the
natural frequency of a vibration.
- Hence crystal vibrates with maximum amplitude at resonance and produced the required
ultrasonic waves in surrounding medium.
- The frequency of a vibration is f =n/2l*√y/p or f =n/2t*√y/p
where n = frequency mode
l = length, t = thickness, y = young modulus p=density
Thus using piezo-electric oscillator ultrasonic waves up to frequency 15*105
Hz can be produced.
Circuit:-
2 Explain the applications of ultrasonic.
science application:- - To find out the defect in metal.
- To find out the passion of ice-burg and submarines in sea.
- It is also useful as pulse, eco-system
General application:- - It is used for drilling, cutting and soldering of law melting point-metal like soft metals.
- It is used for NDT.
- It is useful for measuring the viscosity.
- It is useful for metal and plastic welding.
Engineering application:- - For thickness measurement
- For cavitations: when U.V. transducer is placed in a liquid, it produced a vibration which develop
bubbles in liquid they are known as cavitations bubble,
- For cleaning: high frequency U.V. rays are used to clean fibers and low frequency are used to clean
the metallic parts.
- It also used as a transducer and emulsification.
Medical application:- - The waves are used for observing the growth of a child in mother’s womb’s
- It is used to remove kidney stone and brain tumors without shedding any blood.
- It is used to remove broken teeth.
- It is used to study the blood flow velocities in blood vessels of our body.
- It’s also useful for treatment of cancer.
SONAR:- - Using SONAR the distance and the direction of submarines, depth of sea, depth of rocks in sea, the
shoal of fish in the sea etc can be find out.
3
Sound signaling and depth sounding:- - the principle of echo sounding can e used to give a signal to a distant ship.
- We can also find out depth of water below a ship.
Que-3
1 Explain the various types of crystal system with example. In crystallography, a crystal system or crystal family or lattice system is one of several classes of space
groups, lattices, point groups, or crystals.
- A crystal system is a class of point groups. However, for the five point groups in the trigonal crystal
class there are two possible lattice systems for their point groups: rhombohedral or hexagonal.
- In three dimensions there are seven crystal systems: triclinic, monoclinic, orthorhombic, tetragonal,
trigonal, hexagonal, and cubic. The crystal system of a crystal or space group is determined by its
point group but not always by its lattice
- The relation between three-dimensional crystal families, crystal systems, and lattice systems is shown
in the following table:
Crystal
system
Parameters of unit cell Space Lattice
Element of
symmetry
examples
lengths angles
Cubic a=b=c α=β=γ=90▫ Simple
Body centred
Face centred
9 planes,13 axes NaCl,KCl,Fe,ZnS
Orthorhombic a≠b≠c α=β=γ=90▫ Simple
Body centred
End centred
Face centred
3 planes,3 axes Rhombic sulphur ,
KNO3
Tetragonal a=b≠c α=β=γ=90▫ Simple
Body centred
5 planes,5 axes Sn,SiO2,Sn O2
Monoclinic a≠b≠c α =γ=90▫
β≠90▫
Simple
End centred
1 planes,1 axes Na2SO410H2O,mo
noclinic sulphur
Triclinic a≠b≠c α≠β≠γ≠90▫ Simple No planes, no axes CuSO4,5H2O
Hexagonal a=b≠c α=β=90▫
γ=120▫
Simple
7 planes,7 axes Zn,Cd,ice
Trigonal a=b=c α=β=90▫
β≠90▫
Simple 7 planes,7 axes Quartz,Sb,NaNO3
4
2 What are the difference between crystalline material and Non-crystalline
material.
crystalline material Non-crystalline
material.
Here atom or molecular are arranged in a very
regular and ordinary fashion in three dimensional
pattern.
Here atom or molecular are arranged randomly and
in irregular manner
They are highly ordered state of crystalline solid They are disordered state of crystalline solid or
amorphous solid
Strength of these materials are comparatively high Strength of these materials are lower than
crystalline solid
Example are metals and alloy Examples are glass,wood,plastics.etc
3
3 Write short note on Energy bands in solids
- The atoms in the solid are very closely packed. The nucleus of an atom is so heavy that it
considered being at rest and hence the characteristic of an atom are decided by the electrons.
- During the formation of a solid, energy levels of outer shell electrons got split up. As a
result, closely packed energy levels are produced. The collection of such a large number of
energy levels is called energy band.
- The electrons in the outermost shell are called valence electrons. The band formed by a
series of energy levels containing the valence electrons is known as valence band.
4
- The next higher permitted band in a solid is the conduction band. The electrons occupying
this band are known as conduction electrons.
- Conduction band valence band are separated by a gap known as forbidden energy gap. No
electrons can occupy energy levels in this band.
- Classification of solids on the basis of energy bands
- Insulator - Insulators are very poor conductors of electricity. In this case Eg ≈ 6eV. For E.g.. carbon-
(shown in fig A)
- Semiconductor - A semiconductor material is one whose electrical properties lie between that of insulators
and good conductors. Their forbidden band is small.Ge and Si are examples with forbidden
energy gap 0.7eV and 1.1eV respectively. An appreciable number of electrons can be excited
across the gap at room temperature. By adding impurities or by thermal excitation, we can
increase the electrical conductivity in semiconductors(shown in fig-B)
- Conductor - Here valence band and conduction band overlap and there is no forbidden energy gap.Here
plenty of electrons are available for electrical conduction. The electrons from valence band
can freely enter the conduction band.(fig C)
-
(fig -A) (fig B) (fig C)
4 Explain Photovoltaic Cell and materials used.
Principle:- Solar cells are designed to convert available light into electrical energy.
Structure:- - Modern solar cells are based on semiconductor physics -- they are basically just P-N junction
photodiodes with a very large light-sensitive area.
- The photovoltaic effect, which causes the cell to convert light directly into electrical energy,
occurs in the three energy-conversion layers.
- The first of these three layers necessary for energy conversion in a solar cell is the top
junction layer (made of N-type semiconductor).
- The next layer in the structure is the core of the device; this is the absorber layer (the P-N
junction).
- The last of the energy-conversion layers is the back junction layer (made of P-type
semiconductor).
Working:- - Light generates electron-hole pairs on both sides of the junction, in the n-type emitter and in
the p-type base.
- The generated electrons (from the base) and holes (from the emitter) then diffuse to the
junction and are swept away by the electric field, thus producing electric current across the
device.
- Note how the electric currents of the electrons and holes reinforce each other since these
particles carry opposite charges.
- The p-n junction therefore separates the carriers with opposite charge, and transforms the
generation current between the bands into an electric current across the p-n junction.
3
Circuit:-
V-I characteristic of solar cell:-
Parameter of solar cell:-
- Solar cells are characterized by a maximum Open Circuit Voltage (Voc) at zero output
current and a Short Circuit Current (Isc) at zero output voltage. Since power can be
computed via this equation:
P = I * V
OR
1 Explain with a neat diagram the construction and working of a
semiconductor laser.
Raw Materials:- - The conventional semiconductor laser consists of a compound semiconductor, gallium
arsenide.
- The materials used to form these layers are precisely weighed according to a specific
formula. Other materials that are
- A double heterostructure laser.used to make this type of laser include certain metals (zinc,
gold, and copper) as additives (dopants) or electrodes, and silicon dioxide as an insulator.
4
Design:-
- The basic design of a semiconductor laser consists of a "double heterostructure." This
consists of several layers that have different functions.
- An active or light amplification layer is sandwiched between two cladding layers. These
cladding layers provide injection of electrons into the active layer. Because the active layer
has a refractive index larger than those of the cladding layers, light is confined in the active
layer.
- The performance of the laser can be improved by changing the junction design so that
diffraction loss in the optical cavity is reduced. This is made possible by modifying the laser
material to control the index of refraction of the cavity and the width of the junction. The
index of refraction of the material depends upon the type and quantity of impurity. For
instance, if part of the gallium in the positively-charged layer is replaced by aluminum, the
index of refraction is reduced and the laser light is better confined to the optical cavity.
- The width of the junction can also affect the performance. A narrow dimension confines the
current to a single line along the length of the laser, increasing the current density. Peak
power output must be limited to no more than 400 watts per cm (0.4 in) length of the
junction and current density to less than 6,500 amperes per centimeter squared at the junction
to extend the life of the laser.
The Manufacturing Process:-
Making the substrate:-
- The substrates are made using a crystal pulling technique called the Czochralski method,
where a crystal is grown from a melt.
Growing the layers:-
- The most common method for growing the layers onto the substrate is called liquid-phase
epitaxy (LPE).As the temperature is decreased, the semiconductor compound (such as GaAs)
comes out of the solution in crystalline form and is deposited onto the substrate.
Fabricating the laser device :-
- First, the substrate is mechanically polished
- Next, a very thin silicon dioxide film is formed on the substrate surface.
- Stripes are formed by photolithography and chemical etching.
- Contact electrodes are applied using an evaporation method.
- Next, a laser resonator is formed by cleaving the wafer along parallel crystal planes. The
completed laser devices are then attached to a copper heat sink on one side and a small
electrical contact on the other.
- Application:-
- Medical equipments used in surgery
- As pointer and range finders
- Networking of computers
- As a light sourse and light amplifier in fiber optic communication system
2 Discuss the merits and demerits of semiconductor laser
Merits:- - output power is controlled by junction current
- smaller in size
- highly efficient
- easy to fabricate
- Gives continuous wave output.
Demerits:- - threshold current density is very large
- monochromatically and coherence are poorer
3
3 Discuss in detail the principle of optical finer communication. total Internal Reflection is the principle of optical fiber, (T.I.R.)
it can be define as when light travels from a more optically dense material [larger index of refraction] to a
less dense material the angle of refraction is larger than the incident angle. There are numerous cases where
a larger optical density is accompanied by a smaller mass density.
Because the refracted angle is always larger than the incident angle, it is possible for the refracted angle to
reach 90° before the incident angle reaches 90°. If the light were to refract out of the denser medium, it
would then run along the surface. Larger angles would then yield situations which would force the sine
function to be larger than 1.00, which is mathematically impossible.
4
When the incident angle reaches the condition whereby the refracted ray would bend to an angle of 90°, it is
called the CRITICAL ANGLE. The critical angle obeys the following equation:
This reflected ray changes in intensity as we vary the angle of incidence. At small incident angles (almost
perpendicular to the surface) the reflected ray is weak and the refracted ray is strong.
4 What do you mean by acceptance angle and numerical aperture of a fiber?
“In optics, the numerical aperture (NA) of an optical system is a dimensionless number that
characterizes the range of angles over which the system can accept or emit light.”
Multimode optical fiber will only propagate light that enters the fiber within a certain cone, known as the acceptance cone of the fiber. The half-angle of this cone is called the acceptance angle, θmax. For
step-index multimode fiber, the acceptance angle is determined only by the indices of refraction
where n1 is the refractive index of the fiber core, and n2 is the refractive index of the cladding.
When a light ray is incident from a medium of refractive index n to the core of index n1, Snell's law at
medium-core interface gives
From the above figure and using trigonometry, we get :
3
Where is the critical angle for total internal reflection, since
Substituting for sin θr in Snell's law we get:
By squaring both sides
Thus,
from where the formula given above follows.
θmax = Sin
- √(n1)2-(n2)
2
This has the same form as the numerical aperture in other optical systems, so it has become common to
define the NA of any type of fiber to be
Where n1 =refractive index of core
n2= refractive index of cladding
NA=numerical aperture
θmax = acceptance angle
1 Obtain expression for thermal conductivity - Heat transfer by conduction involves transfer of energy within a material without any motion of the
material as a whole.
- The rate of heat transfer depends upon the temperature gradient and the thermal conductivity of the
material.
- More fundamental questions arise when you examine the reasons for wide variations in thermal
conductivity. Gases transfer heat by direct collisions between molecules, and as would be expected,
their thermal conductivity is low compared to most solids since they are dilute media.
- Non-metallic solids transfer heat by lattice vibrations so that there is no net motion of the media as
the energy propagates through. Such heat transfer is often described in terms of "phonons", quanta of
lattice vibrations. Metals are much better thermal conductors than non-metals because the same
mobile electrons which participate in electrical conduction also take part in the transfer of heat.
- Conceptually, the thermal conductivity can be thought of as the container for the medium-dependent
properties which relate the rate of heat loss per unit area to the rate of change of temperature.(Fig A)
Fig A Fig B
- For an ideal gas the heat transfer rate is proportional to the average molecular velocity, the mean free
path, and the molar heat capacity of the gas.
- For metals, the thermal conductivity is quite high, and those metals which are the best electrical
conductors are also the best thermal conductors.
- At a given temperature, the thermal and electrical conductivities of metals are proportional, but
raising the temperature increases the thermal conductivity while decreasing the electrical
conductivity. This behavior is quantified in the Wiedemann-Franz Law:
4
- Where the constant of proportionality L is called the Lorenz number.
- Qualitatively, this relationship is based upon the fact that the heat and electrical transport both
involve the free electrons in the metal.
- The thermal conductivity increases with the average particle velocity since that increases the forward
transport of energy. However, the electrical conductivity decreases with particle velocity increases
because the collisions divert the electrons from forward transport of charge. This means that the ratio
of thermal to electrical conductivity depends upon the average velocity squared, which is
proportional to the kinetic temperature.
2 State and deduce Wiedemann-Franz law. - The ratio of the thermal conductivity to the electrical conductivity of a metal is proportional to the
temperature. Qualitatively, this relationship is based upon the fact that the heat and electrical
transport both involve the free electrons in the metal. The thermal conductivity increases with the
average particle velocity since that increases the forward transport of energy. However, the electrical
conductivity decreases with particle velocity increases because the collisions divert the electrons
from forward transport of charge. This means that the ratio of thermal to electrical conductivity
depends upon the average velocity squared, which is proportional to the kinetic temperature. The
molar heat capacity of a classical monoatomic gas is given by
- the Wiedemann-Franz Law can be understood by treating the electrons like a classical gas and
comparing the resultant thermal conductivity to the electrical conductivity. The expressions for
thermal and electrical conductivity become:
- Using the expression for mean particle speed from kinetic theory
- the ratio of these quantities can be expressed in terms of the temperature. The ratio of thermal to
electrical conductivity illustrates the Wiedemann-Franz Law,
- While qualitatively agreeing with experiment, the value of the constant is in error in this classical
treatment. When the quantum mechanical treatment is done, the value of the constant is found to be:
3
3 What are Type I and Type II superconductors?
Type 1 Superconductors:- - Type 1 superconductors - characterized as the "soft" superconductors - were discovered first and
require the coldest temperatures to become superconductive. They exhibit a very sharp transition to a
4
superconducting state (see graph) and "perfect" diamagnetism - the ability to repel a magnetic field
completely
- Where as most superconducting pure metals are Type-I superconductors.
-
- Type –II Superconductor:- - A Type-II superconductor is a superconductor characterized by its gradual transition from
the superconducting to the normal state within an increasing magnetic field. Typically they
superconduct at higher temperatures and magnetic fields than Type-I superconductors. This
allows them to conduct higher currents and makes them useful for strong electromagnets.
- Niobium, Vanadium, Technetium, Diamond and Silicon are pure element Type-II
superconductors. Metal alloy superconductors also exhibit Type-II behavior (e.g. niobium-
titanium, niobium-tin).
- In comparison to the (theoretically) sharp transition of a Type-I superconductor above the
lower temperature Tc1, magnetic flux from external fields is no longer completely expelled,
and the superconductor exists in a mixed state. Above the higher temperature Tc2, the
superconductivity is completely destroyed, and the material exists in a normal state. Both of
these temperatures are dependent on the strength of the applied field. It is more usual to
consider a fixed temperature, in which case transition (flux penetration) occurs between
critical field strengths Hc1((lower critical field)) and Hc2( the (upper critical field)
-
4 What is magnetic levitation? Explain with its application.
“Magnetic levitation, maglev, or magnetic suspension is a method by which an object is suspended with no
support other than magnetic fields. Magnetic pressure is used to counteract the effects of the gravitational
and any other accelerations.”
As we have notice in meissner effect that superconductor state has complete diamagnetism and the external
magnetic field is expelled by superconductor. In this state if a bar magnet is dropped on a superconductor, it
will repelled and will hover about it. This is known as magnetic levitation.
3
Magnetic levitation is used for maglev trains, magnetic bearings and for product display purposes.
Application
Maglev - Maglev, or magnetic levitation, is a system of transportation that suspends and guides vehicles,
predominantly trains, using magnetic levitation from a very large number of magnets for lift and
propulsion. This method has the potential to be faster, quieter and smoother than wheeled mass
transit systems.
- The highest recorded speed of a maglev train is 581 kilometers per hour (361 mph), achieved in
Japan in 2003,[11] 6 km/h faster than the conventional TGV speed record. This is slower than many
aircraft, since aircraft can fly at far higher altitudes where air drag is lower, thus high speeds are more
readily attained
.Magnetic bearings
- Magnetic bearings
- Flywheels
- Centrifuges
- This gives us high speed frictionless transportation system.
OR
1 What are the four applications of Nanomaterials?
Here there are a list of number of applications considering current and future application of
nanomaterials-
Cosmetics application of nanoparticle:- - sunscreen lotions: ray absorb properties
Nanocomposite materials:- - Nanoparticle silicate nanolayer (clay nanocomposites) and nanotubes can be used as reinforzed
filler not only to increase mechanical properties of nanocomposites but also to impart new
properties (optical, electronic etc.).
Nanocoatings:- - Surface coating with nanometre thickness of nanomaterial can be used to improve properties like
wear and scratch-resistant, optoelectronics, hydrophobic properties.
Hard cutting tools:-
current cutting tools (e.g. mill machine tools) are made using a sort of metal nanocomposites such
as tungsten carbide, tantalum carbide and titanium carbide that have more wear and erosion-
resistant, and last longer than their conventional (large-grained) materials.
Fuel cells:- Could use nano-engineered membranes to catalytic processes for improve efficiency of small-scale
fuel cells.
Displays:- - New class of display using carbon nanotubes as emission device for the next generation of
monitor and television (FED field-emission displays).
Other feasible nanotechnology applications:- Nanospheres in lubrificants technology like a sort of nano balls bearing Nanoscale magnetic
materials in data storage device. Nanostructure membranes for water purification.
4
2 How will you distinguish metallic glass from ordinary glass? - Unlike the ordinary glass, metallic glasses are not transparent yet there unusual atomic structure gives
them distinctive mechanical and magnetic properties.
- Unlike the ordinary glass, metallic glasses are not brittle
- Many traditional metals can be relatively easily deformed or bent permanently out of shape, because
their crystal lattice are riddled with defects a metallic glass in contrast will spring back to it’s original
shape much more readily.
3
Que-5 List out the difference between
1 Stimulated emission and Spontaneous emission
Stimulated emission Spontaneous emission
stimulated emission causes due to the energy
difference between the higher and lower
energy level state, but it doesn't depends in the
case of spontaneous emission
spontaneous emission causes without any
stimulation .In stimulated emission energy
transfer is twice the energy transfer of
spontaneous emission..
stimulated emission is the process by which an
atomic electron (or an excited molecular state)
interacting with an electromagnetic wave of a
certain frequency, may drop to a lower energy
level transferring its energy to that field
Spontaneous emission is the process by which
a light source such as an atom, molecule,
nanocrystal or nucleus in an excited state
undergoes a transition to a state with a lower
energy
it is a random process it is not a random process non coherent emission coherent emission it doesn’t provide mono chromatic radiation. it can provide mono chromatic radiation.
4
2
Destructive test and Non-destructive test
Destructive test Non-destructive test
In destructive testing, tests are carried out to the
specimen's failure, in order to understand a
specimen's structural performance or material
behaviors under different loads.
Nondestructive testing (NDT) is a wide group of
analysis techniques to evaluate the properties of a
material, component or system without causing
damage
These tests are generally much easier to carry out,
yield more information, and are easier to interpret
than nondestructive testing.
It is a highly-valuable technique that can save both
money and time in product evaluation,
troubleshooting, and research.
Common Destructive test include Stress tests
Crash tests Hardness tests Metallographic tests
Common NDT methods include ultrasonic,
magnetic-particle, liquid penetrate, radiographic,
remote visual inspection (RVI) and eddy-current
testing
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Single mode fiber and Multimode fiber
Single mode fiber Multimode fiber
Single Mode cable is a single strand (most
applications use 2 fibers) of glass fiber with a
diameter of 8.3 to 10 microns that has one mode of
transmission.
Multi-Mode cable has a little bit bigger diameter,
with a common diameters in the 50-to-100 micron
range for the light carry component
Single Modem fiber is used in many applications
where data is sent at multi-frequency (WDM
Wave-Division-Multiplexing) so only one cable is
needed
Most applications in which Multi-mode fiber is
used, 2 fibers are used (WDM is not normally used
on multi-mode fiber).
Example:- step index fiber Example:- multimode step index fiber
The small core and single light-wave virtually
eliminate any distortion that could result from
overlapping light pulses, providing the least signal
attenuation and the highest transmission speeds of
any fiber cable type.
multiple paths of light can cause signal distortion at
the receiving end, resulting in an unclear and
incomplete data transmission
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a.c.Josephson effect and d.c.Josephson effect
a.c.Josephson effect d.c.Josephson effect
If a voltage is applied across the junction, a small
oscillating current starts flowing back and forth
through the junction, without equilibrating the two
sides. This is known as the a.c. Josephson effect.
If a constant current is made to flow through the
junction, no voltage drop is detected across it, as
long as the current stays below some critical value.
This is known as the d.c. Josephson effect.
When a potential difference V is applied between
two side of a Josephson junction there is an
oscillation of the tunneling current with angular
velocity.
The tunneling of electrons across the insulator in a
Josephson junction result in a net current which
flow even in the absence of a potential difference
OR
Write short notes on
1 Free electron theory of metals
Classical free electron theory of metals This theory was developed by Drude and Lorentz and hence is also known as Drude-Lorentz theory.
According to this theory, a metal consists of electrons which are free to move about in the crystal like
molecules of a gas in a container. Mutual repulsion between electrons is ignored and hence potential energy
is taken as zero. Therefore the total energy of the electron is equal to its kinetic energy.
Drift velocity:- - If no electric field is applied on a conductor, the free electrons move in random directions. They
collide with each other and also with the positive ions. Since the motion is completely random,
average velocity in any direction is zero. If a constant electric field is established inside a conductor,
the electrons experience a force F = -eE due to which they move in the direction opposite to direction
- of the field. These electrons undergo frequent collisions with positive ions. In each such collision,
direction of motion of electrons undergoes random changes. As a result, in addition to the random
- motion, the electrons are subjected to a very slow directional motion. This motion is called drift and
the average velocity of this motion is called drift velocity vd.
- Consider a conductor subjected to an electric field E in the x-direction. The force on the electron due
to the electric field F = eE. (Neglect – sign.)
- By Newton’s law, eE = mdvd/dt (F=ma)
dvd = eEdt/m
Integrating,
Vd = eEt/m + Constant
When t = 0, vd = 0 Therefore Constant = 0
Vd = eEt/m --------------- (1)
Electrical conductivity:-
- Consider a wire of length ‘dl’ and area of cross section ‘A’ subjected to an electric field E. If ‘n’ is
the concentration of the electrons, the number of electrons flowing through the wire in dt = nAvddt.
- The quantity of charge flowing in time dt = nAvddt.e
- Therefore I = dq/dt = neAvd
- Current density J = I/A = nevd Substituting the value of vd from (1),
So, J = nee Et/m = ne2Et/m --------------- (2)
By Ohm’s law, J = s E (where s=electrical conductivity)
Therefore s = J/E = ne2t/m -------------- (3)
Mobility of a charge carrier is the ratio of the drift mobility to the electric field.
µ = vd/E m2/Volt-Sec
Substituting vd from (1), µ = et/m -------------- (4)
Substituting this in equation (3), s = neµ ------------- (5)
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2 Application of LASER in different field.
Scientific:- - A wide variety of interferometer techniques
- Laser induced breakdown spectroscopy
- Investigating nonlinear optics phenomena
- Holographic techniques employing lasers also contribute to a number of measurement techniques.
- Laser based Light Detection And Ranging (LIDAR) technology has application in geology,
seismology, remote sensing and atmospheric physics.
Spectroscopy:- - Most types of laser are an inherently pure source of light; they emit near-monochromatic light
with a very well defined range of wavelengths. By careful design of the laser components, the
purity of the laser light (measured as the "line width") can be improved more than the purity of any
other light source. This makes the laser a very useful source for spectroscopy
Military:- - military uses of lasers include applications such as target designation and ranging, defensive
countermeasures, communications and directed energy weapons.
Medical:- - Cosmetic surgery
- Eye surgery and refractive surgery
- Soft tissue surgery: CO2, Er:YAG laser
- Laser scalpel (General surgery, gynecological, urology, laparoscopic)
- "No-Touch" removal of tumors, especially of the brain and spinal cord.
Industrial and commercial:- Lasers used for visual effects during a musical performance.
- Cutting and peening of metals and other material, welding, marking, etc.
- Laser engraving, Laser bonding, Laser pointers, Holography
- Extensively in both consumer and industrial imaging equipment.
- Diode lasers are used as a light switch in industry, with a laser beam and a receiver which will
switch on or off when the beam is interrupted, and because a laser can keep the light intensity over
larger distances than a normal light, and is more precise than a normal light it can be used for
product detection in automated production
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3 Types of biomaterials and their applications in the medical field
- Biomaterials can generally be produced either in nature or synthesized in the laboratory
using a variety of chemical approaches utilizing metallic components or ceramics
- The development of biomaterials, as a science, is about fifty years old. The study of
biomaterials is called biomaterials science. It has experienced steady and strong growth over
its history, with many companies investing large amounts of money into the development of
new products. Biomaterials science encompasses elements of medicine, biology, chemistry,
tissue engineering and materials science. They are classified as follows:
- Metal and alloy
- Polymers
- Ceramics
- Composites
- Natural
Application:-
Biomaterials are used in:
• Joint replacements
• Bone plates
• Bone cement
• Artificial ligaments and tendons
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• Dental implants for tooth fixation
• Blood vessel prostheses
• Heart valves
• Skin repair devices (artificial tissue)
• Cochlear replacements
• Contact lenses
• Breast implants
Biomaterials must be compatible with the body, and there are often issues of biocompatibility
which must be resolved before a product can be placed on the market and used in a clinical setting.
Because of this, biomaterials are usually subjected to the same requirements of those undergone by
new drug therapies. All manufacturing companies are also required to ensure traceability of all of
their products so that if a defective product is discovered, others in the same batch may be traced.
4 Properties of Smart Memory Alloys
Mainly there are two properties.
shape memory effect
- The shape memory effect is observed when the temperature of a piece of shape memory
alloy is cooled to below the temperature Mf. At this stage the alloy is completely composed
of Martensite which can be easily deformed. After distorting the SMA the original shape can
be recovered simply by heating the wire above the temperature Af. The heat transferred to
the wire is the power driving the molecular rearrangement of the alloy, similar to heat
melting ice into water, but the alloy remains solid. The deformed Martensite is now
transformed to the cubic Austenite phase, which is configured in the original shape of the
wire.
-
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Pseudo-elasticity
Pseudo-elasticity occurs in shape memory alloys when the alloy is completely composed of
Austenite (temperature is greater than Af). Unlike the shape memory effect, pseudo-elasticity
occurs without a change in temperature. The load on the shape memory alloy is increased until the
Austenite becomes transformed into Martensite simply due to the loading; this process is shown in
Figure 5. The loading is absorbed by the softer Martensite, but as soon as the loading is decreased
the Martensite begins to transform back to Austenite since the temperature of the wire is still above
Af, and the wire springs back to its original shape.