(B.E. Sem-1 G.T.U.) Physics Paper With Solution

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.