experiments reports of solid state physics

Ahmed Haider -B.Sc. student – Faculty of Science – Dept. of Physics – Minia Univ.

In The Name of Allah Most Gracious, Most Merciful

Solid State Physics lab

Experiments Reports

Prepared by

Ahmed Haider Ahmed Ibrahim

B.Sc. student – Faculty of Science – Dept. of physics – Minia University

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Under supervision

Prof. Dr. Adel Ashour

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Assistant Prof. Hamida Ragab

1- Solar Thermal Collector

Objectives;

- Study the effect of concave mirror to collect heat

- Compare between heat in air and in concave mirror

Equipment:-

Experimental solar source (have sun’s wavelengths) – thermometer – concave surface - stop watch

Work:-

Put light source at determined distance

Every minute measure the temperature

Put concave surface at the same distance and repeat the second step

Theory

A solar thermal collector is a solar collector designed to collect heat by absorbing sunlight.

The term is applied to solar hot water panels, but may also be used to denote more complex installations such as solar parabolic, solar trough and solar towers or simpler installations such as solar air heat.

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http://en.wikipedia.org/wiki/Solar_hot_water_panel

http://en.wikipedia.org/wiki/Sunlight


The more complex collectors are generally used in solar power plants where solar heat is used to generate electricity by heating water to produce steam which drives a turbine connected to an electrical generator.

The simpler collectors are typically used for supplemental space heating in residential and commercial buildings.

A collector is a device for converting the energy in solar radiation into a more usable or storable form. The energy in sunlight is in the form of electromagnetic radiation from the infrared (long) to the ultraviolet (short) wavelengths.

The solar energy striking the Earth's surface depends on weather conditions, as well as location and orientation of the surface, but overall, it averages about 1,000 watts per square meter under clear skies with the surface directly perpendicular to the sun's rays.

Solar thermal collectors are divided into the categories of low, medium and high temperature collectors:

Low temperature collectors

provide low-grade heat (less than 110 degrees Fahrenheit or 40 C),

through either metallic or nonmetallic absorbers and are used in such applications as swimming pool heating and low-grade water and space heating.

Medium-temperature collectors

provide medium-grade heat (greater than 40 C, usually 60 to 80 C)

either through glazed flat-plate collectors using air or liquid as the heat transfer instrument or concentrator collectors that

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http://en.wikipedia.org/wiki/Infrared

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http://en.wikipedia.org/wiki/Turbine

http://en.wikipedia.org/wiki/Electricity


concentrate the heat of incident insolation to greater than one sun i.e. Natural solar insolation falling on an object without concentration or diffusion of the solar rays and are mainly used for domestic hot water heating. Evacuated tube collectors are also included in this category.

High-temperature collectors

They are parabolic dish or trough collectors designed to operate at a temperature of 80 C or higher and are primarily used by utilities and independent power producers to generate electricity for the grid.

In the lab we study two cases :-

I-Air

Solar Air Heat collectors heat air directly, almost always for space heating. They are also used for pre-heating make-up air in commercial and industrial systems. They fall into two categories: Glazed and Unglazed.

Glazed systems have a transparent top sheet as well as insulated side and back panels to minimize heat loss to ambient air. The absorber plates in modern panels can have an absorptivity of more than 93%. Air typically passes along the front or back of the absorber plate while scrubbing heat directly from it. Heated air can

then be distributed directly for applications such as space heating and drying or may be stored for later use.

Unglazed systems, or transpired air systems, consist of an absorber plate which air passes across or through as it scrubs heat from the absorber. These systems are typically used for pre-heating make-up air in commercial buildings.

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These technologies are among the most efficient, dependable, and economical solar technologies available. Payback for glazed solar air heating panels can be less than 9-15 years depending on the fuel being replaced

II-Parabolic (concave) dish

Solar Parabolic (concave) dish

Definitions

- Concave mirror is spherical reflected surface - The radius of curvature (r) is the distance between center of its

curvature and vertex - Focus is the collected point of incident rays after reflecting from

surface of mirror - Focal length (f) is the distance between vertex and focus

This is the most powerful type of collector which concentrates sunlight at a single, focal point, via one or more parabolic dishes arranged in a similar fashion to a reflecting telescope focuses starlight, or a dish antenna focuses radio waves. This geometry may be used in solar furnaces and solar power plants.

There are two key phenomena to understand in order to comprehend the design of a parabolic dish :-

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One is that the shape of a parabola is defined such that incoming rays which are parallel to the dish's axis will be reflected toward the focus, no matter where on the dish they arrive.

The second key is that the light rays from the sun arriving at the Earth's surface are almost completely parallel. So if dish can be aligned with its axis pointing at the sun, almost all of the incoming radiation will be reflected towards the focal point of the dish most losses are due to imperfections in the parabolic shape and imperfect reflection.

Losses due to atmosphere between the dish and its focal point are minimal, as the dish is generally designed specifically to be small enough that this factor is insignificant on a clear, sunny day. Compare this though with some other designs, and you will see that this could be an important factor, and if the local weather is hazy, or foggy, it may reduce the efficiency of a parabolic dish significantly.

In some power plant designs, a sterling engine coupled to a dynamo, is placed at the focus of the dish, which absorbs the heat of the incident solar radiation, and converts it into electricity.

Advantages

Very high temperatures reached. High temperatures are suitable for electricity generation using conventional methods like steam turbine or some direct high temperature chemical reaction.

Good efficiency. By concentrating sunlight current systems can get better efficiency than simple solar cells.

A larger area can be covered by using relatively inexpensive mirrors rather than using expensive solar cells.

Concentrated light can be redirected to a suitable location via optical fiber cable. For example illuminating buildings.

Disadvantages

Concentrating systems require sun tracking to maintain Sunlight focus at the collector.

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Inability to provide power in diffused light conditions. Solar Cells are able to provide some output even if the sky becomes a little bit cloudy, but power output from concentrating systems drop drastically in cloudy conditions as diffused light cannot be concentrated passively.

Observations

1- Air

-Room temperature is 34 C

-After 19 minutes the temperature is raise to 38

2- Parabolic surface

-Room temperature is 35 C

- After 18 minutes reached to 40

Conclusions

Concave mirror is high collected heat.

Results

Time (min)

Temp. (C)

Air

Temp. (C)

Mirror03435134.337234.93833539435.339.1

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535.840635.940.05736.240.5836.3540.6936.540.71036.6411136.740.51236.841.1133741.11637.340.11737.5401837.840193840203840213840

Graphing

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2- Solar cell

Objectives

Determine maximum Power.

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Determine short circuit current.

Determine open circuit voltage.

Determine Fill factor.

Determine effeciency.

Tools and Equipment

Solar cell – wires – resistors- ammeter - voltmeter

Used Circuits

Work

i - in Dark

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Fig (1)

mA

V

V

Rs

Rsh

Fig (2)

A


solar cell act as Daiode.

we connect circuit in fig (1)

change voltage from bettery and every time read the current and volt.

Draw the relation between I on y-axis and V on x-axis .

Slope at the beginning of curve give Rs and slope of tangent of curve give Rsh

ii - in lamination

connect circuit in fig (2)

Put light source at known distance (r).

Change resistor and every time read current and volt.

Draw relation between V on x-axis and I on y-axis.

From graph we get VOC , I sc and Pmax.

Change the distance and repeat the previous steps.

Introduction

A solar cell or photovoltaic cell is a device that converts

sunlight directly into electricity by the photovoltaic effect.

Sometimes the term solar cell is reserved for devices intended

specifically to capture energy from sunlight, while the term

photovoltaic cell is used when the light source is unspecified.

Assemblies of cells are used to make solar panels, solar

modules, or photovoltaic arrays. Photovoltaic is the field of

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http://en.wikipedia.org/wiki/Solar_module




http://en.wikipedia.org/wiki/Sunlight


technology and research related to the application of solar cells

in producing electricity for practical use. The energy generated

this way is an example of solar energy (also called solar power).

Generations of solar cells

Solar Cells are classified into three generations which indicates the order of which each became important. At present there is concurrent research into all three generations while the first generation technologies are most highly represented in commercial production, accounting for 89.6% of 2007 production.

i. First Generation

First generation cells consist of large-area, high quality and

single junction devices. First Generation technologies involve

high energy and labor inputs which prevent any significant

progress in reducing production costs.

ii. Second Generation

Second generation materials have been developed to address

energy requirements and production costs of solar cells.

Alternative manufacturing techniques such as vapour

deposition, electroplating, and use of Ultrasonic Nozzles are

advantageous as they reduce high temperature processing

significantly. The most successful second generation materials

have been cadmium telluride (CdTe), copper indium gallium

selenide, amorphous silicon and micro amorphous silicon.

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http://en.wikipedia.org/wiki/Single_junction


iii. Third Generation

Third generation technologies aim to enhance poor electrical

performance of second generation (thin-film technologies) while

maintaining very low production costs.

High efficiency cells

High efficiency solar cells are a class of solar cell that can generate electricity at higher efficiencies than conventional solar cells. While high efficiency solar cells are more efficient in terms of electrical output per incident energy (watt/watt), much of the industry is focused on the most cost efficient technologies, i.e. cost-per-watt

Many businesses and academics are focused on increasing the electrical efficiency of cells, and much development is focused

on high efficiency solar cells .

Applications and implementations

Polycrystalline PV cells

Solar cells are often electrically connected and encapsulated as a

module. PV modules often have a sheet of glass on the front

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http://en.wikipedia.org/wiki/File:Solar_panel.png

http://en.wikipedia.org/wiki/Cost_efficient



(sun up) side, allowing light to pass while protecting the

semiconductor wafers from the elements (rain, hail, etc.). Solar

cells are also usually connected in series in modules, creating an

additive voltage. Connecting cells in parallel will yield a higher

current. Modules are then interconnected, in series or parallel, or

both, to create an array with the desired peak DC voltage and

current.

The power output of a solar array is measured in watts or

kilowatts. In order to calculate the typical energy needs of the

application, a measurement in watt-hours, kilowatt-hours or

kilowatt-hours per day is often used. A common rule of thumb is

that average power is equal to 20% of peak power, so that each

peak kilowatt of solar array output power corresponds to energy

production of 4.8 kWh per day (24 hours x 1kW x 20% = 4.8

kWh)

To make practical use of the solar-generated energy, the

electricity is most often fed into the electricity grid using

inverters (grid-connected PV systems); in stand alone systems,

batteries are used to store the energy that is not needed

immediately.

Solar cells can also be applied to other electronics devices to

make it self power sustainable in the sun. There are solar cell

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phone chargers, solar bike light and solar camping lanterns that

people can adopt for daily use.

Types of solar cells

1- Crystalline silicon

The most prevalent bulk material for solar cells is crystalline

silicon (abbreviated as a group as c-Si), also known as "solar

grade silicon". Bulk silicon is separated into multiple categories

according to crystallinity and crystal size in the resulting ingot,

ribbon, or wafer.

i- monocrystalline silicon (c-Si) :

often made using the Czochralski process. Single-crystal

wafer cells tend to be expensive, and because they are cut

from cylindrical ingots, do not completely cover a square

solar cell module without a substantial waste of refined

silicon. Hence most c-Si panels have uncovered gaps at the

four corners of the cells .

Ribbon silicon is a type of monocrystalline silicon: it is

formed by drawing flat thin films from molten silicon and

having a multicrystalline structure. These cells have lower

efficiencies than poly-Si, but save on production costs due

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to a great reduction in silicon waste, as this approach

does not require sawing from ingots .

ii- Poly- or multicrystalline silicon (poly-Si or mc-Si) :

made from cast square ingots large blocks of molten silicon

carefully cooled and solidified. Poly-Si cells are less

expensive to produce than single crystal silicon cells, but are

less efficient .

2- Silicon Thin Films

Silicon thin-film cells are mainly deposited by chemical

vapor deposition (typically plasma-enhanced (PE-CVD)) from

silane gas and hydrogen gas. Depending on the deposition

parameters, this can yield:

i. Amorphous silicon (a-Si or a-Si:H)

ii. Protocrystalline silicon

iii. Nanocrystalline silicon (nc-Si or nc-Si:H),also called

microcrystalline

These types of silicon present dangling and twisted bonds,

which results in deep defects (energy levels in the bandgap) as

well as deformation of the valence and conduction bands (band

tails). The solar cells made from these materials tend to have

lower energy conversion efficiency than bulk silicon, but are also

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less expensive to produce. The quantum efficiency of thin film

solar cells is also lower due to reduced number of collected

charge carriers per incident photon.

i- Amorphous silicon has a higher bandgap (1.7 eV) than

crystalline silicon (c-Si) (1.1 eV), which means it absorbs the

visible part of the solar spectrum more strongly than the infrared

portion of the spectrum. As nc-Si has about the same bandgap as

c-Si, the nc-Si and a-Si can advantageously be combined in thin

layers, creating a layered cell called a tandem cell. The top cell

in a-Si absorbs the visible light and leaves the infrared part of

the spectrum for the bottom cell in nanocrystalline Si.

A silicon thin film technology is being developed for building

integrated photovoltaics (BIPV) in the form of semi-transparent

solar cells which can be applied as window glazing. These cells

function as window tinting while generating electricity.

ii- Nanocrystalline solar cells

These structures make use of some of the same thin-film light

absorbing materials but are overlain as an extremely thin

absorber on a supporting matrix of conductive polymer or

mesoporous metal oxide having a very high surface area to

increase internal reflections (and hence increase the probability

of light absorption).

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Low Cost Solar Cell

Dye-sensitized solar cell, and Luminescent solar concentrators

are considered low-cost solar cells.This cell is extremely

promising because it is made of low-cost materials and does not

need elaborate apparatus to manufacture.

Theoryi. in sunlight hit the solar panel and are absorbed by

semiconducting materials, such as silicon.

ii. Electrons (negatively charged) are knocked loose from their

atoms, allowing them to flow through the material to

produce electricity.

iii. An array of solar cells converts solar energy into a usable

amount of direct current (DC) electricity.

Photogeneration of charge carriers

When a photon hits a piece of silicon, one of three things can happen:

i. the photon can pass straight through the silicon this

(generally) happens for lower energy photons,

ii. the photon can reflect off the surface,

iii. the photon can be absorbed by the silicon, if the photon

energy is higher than the silicon band gap value. This

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generates an electron-hole pair and sometimes heat,

depending on the band structure.

When a photon is absorbed, its energy is given to an electron in

the crystal lattice. Usually this electron is in the valence band,

and is tightly bound in covalent bonds between neighboring

atoms, and hence unable to move far. The energy given to it by

the photon "excites" it into the conduction band, where it is free

to move around within the semiconductor. The covalent bond

that the electron was previously a part of now has one fewer

electron this is known as a hole. The presence of a missing

covalent bond allows the bonded electrons of neighboring atoms

to move into the "hole," leaving another hole behind, and in this

way a hole can move through the lattice. Thus, it can be said

that photons absorbed in the semiconductor create mobile

electron-hole pairs.

A photon need only have greater energy than that of the band

gap in order to excite an electron from the valence band into the

conduction band. However, the solar frequency spectrum

approximates a black body spectrum at ~6000 K, and as such,

much of the solar radiation reaching the Earth is composed of

photons with energies greater than the band gap of silicon.

These higher energy photons will be absorbed by the solar cell,

but the difference in energy between these photons and the

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silicon band gap is converted into heat (via lattice vibrations

called phonons) rather than into usable electrical energy.

The p-n junction

The most commonly known solar cell is configured as a

large-area p-n junction made from silicon. As a simplification,

one can imagine bringing a layer of n-type silicon into direct

contact with a layer of p-type silicon. In practice, p-n junctions

of silicon solar cells are not made in this way, but rather, by

diffusing an n-type dopant into one side of a p-type wafer (or

vice versa).

Connection to an external load

Ohmic metal-semiconductor contacts are made to both the

n-type and p-type sides of the solar cell, and the electrodes

connected to an external load. Electrons that are created on the

n-type side, or have been "collected" by the junction and swept

onto the n-type side, may travel through the wire, power the

load, and continue through the wire until they reach the p-type

semiconductor-metal contact. Here, they recombine with a hole

that was either created as an electron-hole pair on the p-type side

of the solar cell, or are swept across the junction from the n-type

side after being created there.

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The voltage measured is equal to the difference in the quasi

Fermi levels of the minority carriers i.e. electrons in the p-type

portion, and holes in the n-type portion.

To understand the electronic behavior of a solar cell, it is useful

to create a model which is electrically equivalent, and is based

on discrete electrical components whose behavior is well

known. An ideal solar cell may be modelled by a current source

in parallel with a diode; in practice no solar cell is ideal, so a

shunt resistance and a series resistance component are added to

the model. The resulting equivalent circuit of a solar cell as

shown in fig (1) .

Characteristic equation

From the equivalent circuit it is evident that the current

produced by the solar cell is equal to that produced by the

current source, minus that which flows through the diode, minus

that which flows through the shunt resistor

I = IL − ID − ISH

where I = output current (amperes) ,IL = photogenerated current (amperes)

,ID = diode current (amperes) ,ISH = shunt current (amperes)

The current flowing through these elements is governed by the voltage across them:

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http://en.wikipedia.org/wiki/Solar_cell#cite_note-18



Vj = V + IRS

where Vj = voltage across both diode and resistor RSH (volts)

By the Shockley diode equation, the current diverted through the diode is:

where I0 = reverse saturation current (amperes) , n = diode ideality factor (1 for an ideal diode) , q = elementary charge , k = Boltzmann's constant , T = absolute temperature .

By Ohm's law, the current diverted through the shunt resistor is:

where RSH = shunt resistance (Ω)

Substituting these into the first equation produces the characteristic equation of a solar cell, which relates solar cell parameters to the output current and voltage:

An alternative derivation produces an equation similar in

appearance, but with V on the left-hand side. The two

alternatives are identities; that is, they yield precisely the same

results.

In principle, given a particular operating voltage V the equation

may be solved to determine the operating current I at that

voltage. However, because the equation involves I on both sides

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http://en.wikipedia.org/wiki/Volts

http://upload.wikimedia.org/math/4/5/3/453ba1179cfd23ccd91d26073a483ee9.png

http://en.wikipedia.org/wiki/Boltzmann's_constant

http://en.wikipedia.org/wiki/Elementary_charge

http://en.wikipedia.org/wiki/Elementary_charge





http://en.wikipedia.org/wiki/Amperes


in a transcendental function the equation has no general

analytical solution. However, even without a solution it is

physically instructive. Furthermore, it is easily solved using

numerical methods. (A general analytical solution to the

equation is possible using Lambert's W function, but since

Lambert's W generally itself must be solved numerically this is a

technicality.)Since the parameters I0, n, RS, and RSH cannot be

measured directly, the most common application of the

characteristic equation is nonlinear regression to extract the

values of these parameters on the basis of their combined effect

on solar cell behavior.

Shunt resistance

Effect of shunt resistance on the current-voltage characteristics of a solar cell

As shunt resistance decreases, the flow of current diverted

through the shunt resistor increases for a given level of junction

voltage. The result is that the voltage-controlled portion of the I-

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V curve begins to sag toward the origin, producing a significant

decrease in the terminal current I and a slight reduction in VOC.

Very low values of RSH will produce a significant reduction in

VOC. Much as in the case of a high series resistance, a badly

shunted solar cell will take on operating characteristics similar

to those of a resistor. These effects are shown for crystalline

silicon solar cells in the I-V curves displayed in the figure to the

right.

Maximum-power point

A solar cell may operate over a wide range of voltages (V)

and currents (I). By increasing the resistive load on an irradiated

cell continuously from zero (a short circuit) to a very high value

(an open circuit) one can determine the maximum-power point,

the point that maximizes V×I; that is, the load for which the cell

can deliver maximum electrical power at that level of

irradiation. (The output power is zero in both the short circuit

and open circuit extremes).

Pmax = Vmax . Imax

Fill factor

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Another defining term in the overall behavior of a solar

cell is the fill factor (FF). This is the ratio of the maximum

power point divided by the open circuit voltage (Voc) and the

short circuit current (Isc):

Increasing the shunt resistance (Rsh) and decreasing the series

resistance (Rs) will lead to higher fill factor, thus resulting in

greater efficiency, and pushing the cells output power closer

towards its theoretical maximum.

Solar cell efficiency factors

A solar cell's energy conversion efficiency (η) is the

percentage of power converted (from absorbed light to electrical

energy) and collected, when a solar cell is connected to an

electrical circuit. This term is calculated using the ratio of the

maximum power point, Pm

= 4 r2 Pmax /100

STC specifies a temperature of 25°C and an irradiance of 1000

W/m2 with an air mass 1.5 (AM1.5) spectrum.

Conclusion

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The fill factor is directly affected by the values of the cells series

and shunt resistance.

Experimental data

1- Dark

2- lamination

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I mAV volt0.30.1

0.60.210.3

1.40.41.80.52.30.62.80.73.40.84.10.94.816.91.2101.4121.5

14.91.6201.7251.8

30.71.9442632.15


V oc=1 .6v , I sc=18×10−3 A

V max=0 .9 v , Imax=13×10−3 A

∴Pmax=117×10−4 watt

F . F=117×10−4

18×1 .6=0 .406

η=4 π (25×10−2 )2×117×10−4

100=92×10−6

3- The Greenhouse Effect

Objectives

Study green house effect on black body.

Study green house effect on white body.

Equipments and Tools

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V1.551.6521.5431.541.4651.4161.3671.3181.2691.19101.12111.05120.99130.9140.78150.63160.46170.2617.90.02


Green house- light source – thermometer- white surface – stop watch

Work

Put white body at distance about 15cm.

Every minute measure temperature.

Repeat the last steps with black body.

Repeat the above steps at different distance let 20cm.

Theory of Experiment

The reason that glass is such a valuable material is that it exhibits a very low absorption of electromagnetic radiation in the visible part of the spectrum, which is a wordy way of saying that it is transparent. It is not, however, transparent either side of the visible range (ultra violet and infra red).

When matter in general interacts with radiation it can absorb, reflect or transmit it. One of the basic principles in the understanding of energy is that it always degrades. The high grade (i.e. most usable) energy the comes into your home via the electricity mains always ends up as low grade energy or heat, via intermediate forms such as light, sound or mechanical motion. Likewise the light impinging on the earth that is not reflected back into space also ends up as heat. All matter re-radiates heat, mainly in the infrared part of the spectrum. Glass, however, is relatively opaque to infrared. Thus the greenhouse glass acts as a one-way energy valve.

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In the atmosphere water vapor is a major component (1%-4%) and it has similar optical properties to glass. The water molecule is in the form of a shallow V with two hydrogen atoms attached to the heavier central oxygen atom. It absorbs radiation by the various modes of vibration of this system and by rotation (think of it as two light balls attached to a heavy one by springs). Pure liquid water is actually blue, as it absorbs slightly in the red, though heavy water is colorless because the heavier atoms do not vibrate so readily at optical frequencies. Like the greenhouse glass, the water vapor acts as a one-way energy valve. Thus not only does water keep the planet warm, but it also maintains a fairly constant temperature. It is this greenhouse effect that makes life on earth possible.

The other and major mechanism in the greenhouse is the inhibition of convection. This is not ideal, as there is heat loss from the roof by convection. The Earth, in contrast, loses no heat by convection, but only by radiation. Convection in the oceans and atmosphere merely serves to redistribute the heat.

In order to understand fully the warming effect of the atmosphere it is necessary to appreciate the nature of radiation. The ideal radiator is known as a black body, which is one that absorbs all frequencies completely. It also radiates all frequencies equally, so the distribution of energy in the radiation is a function of the distribution of energy across the spectrum. This is determined by Wien's laws (later modified by Planck) and is a function of temperature only. Real bodies are not black.

The so-called greenhouse effect is simply explained as a three body problem. The three bodies are one that is very small but very hot, the Sun, one that is very large and very cold, outer space, and the earth. The first two may be considered approximately to act as black bodies, so they emit according to Wien's laws. The energy

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transfer is governed by the area under the black body spectrum, which depends only on the temperature. The blue planet, however, is not a black body. Its absorption/emission spectrum contains gaps, due mainly to the presence of water vapor in the atmosphere. As it is in thermal equilibrium with the other two bodies, it has to radiate as much as it absorbs. In order for the area under the spectrum to be sufficient, the equilibrium temperature must therefore be higher than if it were a black body.

There are other potential greenhouse gases, such as carbon dioxide and methane, but their atmospheric concentrations are so low that they may be ignored (CO2 at 0.033% and CH4 at 0.0002%).

Applications

Essential use of greenhouse glass:

In terms of active plant growth in the greenhouse, one can find winter to be the calm season. But there still a plenty of work to be done in between the sun rise and sun set of each upcoming day. The growing plants should be protected from the cold frosts. All the shading works should be perfectly cleaned when one is preparing for winter. To let in more of light in the greenhouse glass, the greenhouse glass should be kept clean. The growth of the plant slows down as the winter begins and lot of patience is expected until the day begins to lengthen again.

Greenhouse heaters:

The greenhouse heaters are checked then and then to make sure that the heaters work effectively. For one to keep things warm the greenhouse can be insulated with bubble-wrap and this is termed to be one of the most inexpensive ways. It will greatly help in reducing heating bills too. To provide floral display all throughout the year, perpetual carnation is required and this can be enabled all with a temperature of about 7 degree during night time.

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Shut down of ventilation:

Ventilation is a very important factor for greenhouse fertilizer applications during winter season. Free ventilation is allowed but one should check carefully and prevent the cold breeze from entering into the greenhouse glass because it can chill down many things. Therefore one should shut down their vents quickly before the temperature falls in and becomes very cold. During windy or foggy days when the climatic condition is extremely cold outside, the greenhouse could be kept closed. And if this condition persists the green house should be insulated so that the growing plants could be kept safe from the heavy freezing cold.

Winter watering:

There are lot many chances for the soil to dry out, during this time winter watering could be done. Winter watering is not to be done often, because if too much of water is supplied it can sometimes damage the roots and cause lot of problems especially in the tender growing plants. So it is always better for us to keep the soil slightly dry and in good light to avoid damaged circumstances.

Care for plants:

A special care for plants should be always given. At the very beginning of winter the plants should undergo outstanding potting and cuttings of fuchsias and pelargoniums could also be potted. If these hardy plants are potted up in winter then we could expect flower blossoms very much earlier. A wide range of bulb varieties could also be potted out this way and one could definitely wait for an early blossom. Many green house plants namely begonias, gloxinias, could be sown by the month of January or February. An early rise in temperature could result in the sowing of early cropping vegetables.

Care against fungal attacks:

When the frost is too high the winter green house provides refuge for a great number of flowering plants. Although the flowering plants are highly dormant, we should check those plants occasionally so that the compost does not get dried off. These flowering tubers or

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bulbs should be examined periodically to check whether it has got any sign of attack of fungus. It is also checked occasionally to see whether it is rotten. If it is rotten or if there is any sign of fungus then immediately these flowering tubers or bulbs are discarded and destroyed. Generally pests don’t seem active this season, anyways it is better to check out for whitefly or vine weevil throughout this season. The fertilizers used in the garden frame plays a very important role in acclimatizing plants raised under the glass to a least controlled external environment.

Observation

Black body curve is greater than white body at the same distance

Conclusions

Black body is perfect absorber this property can be used in more applications as above.

Results ( at distance 20 , 15 cm )

At distance 20 cmAt distance 15 cmTime (min)

Temp. white

Temp. black

Time (min)

Temp. white

Temp. black

03030030301353813336237.54123541339.54433744.5441.54644047

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54348541.549644496435174550744.553.88465184655946.552947561047531047.5571144.554114857.51248541249581348.554134958.5144954144959154954154959164954164959

At 20 cm

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at 15 cm

4-Tensile Test Objectives :

- Determine Young modulus

- Determine elastic limit

- Determine yield stress

- Determine ultimate tensile strength

Equipment and tools :-

1- Extension device

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2- Sample of material ( Cu , Al,…etc) its length is 30mm and area is 0.4cm

Work :-

1- We fix the sample and begin to turn.

2- Read force every time .

3- Draw the relation between extension divided by length on x-axis and force divided by area on y-axis.

4- Calculate the slope of curve we get Young Modulus.

5- From curve we can get elastic limit and limit.

Introduction

The tensile experiment is the most common mechanical test that reveals several important mechanical properties, such as: modulus of elasticity, yield strength, ultimate tensile strength, ductility, and toughness. The material to be tested is formed into a shape suitable for gripping in the testing machine, and then pulled at constant rate until it fractures. The tensile instrument elongates the specimen at a

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constant rate and has devices to continuously measure and record the applied load and elongation of the specimen. During the stretching of the specimen, changes occur in its physical dimensions and its mechanical properties. The ability to predict the loads that will cause a part to fail depends upon both material properties and the part geometry. This experiment involves testing to determine the relative properties.

Theory.A tensile test, is probably mechanical test you can perform on material. Tensile tests are simple, relatively the most fundamental type of inexpensive, and fully standardized. By pulling on something, you will very quickly determine how the material will react to forces being applied in tension. As the material is being pulled, you will find its strength along with how much it will elongate.

This Exp. depend on Hooke law that states that force is directly proportional to extension For most tensile testing of materials, you will notice that in the initial portion of the test, the relationship between the applied force, and load, and the elongation the specimen exhibits is linear. In this linear region, the line obeys the relationship defined as "Hooke's Law" where the ratio of stress to strain is a constant, or Y is the slope of the line in this region where stress (σ) is proportional to strain (ε) and is called the Modulus of Elasticity" Young's Modulus".

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F = k L

K is force constant

Stress is a measure of the intensity of an internal force. Stress is defined as the force per unit area

σ= FA

Types of Stress

1-Tensil stress

if force effect normal to determined area cause extension to this area

2-compress stress

if force cause decreasing for length

3-shear stress

the force is parallel to surface

Strain is a measure of the deformation that has occurred in a material. In the case where the magnitude of deformation is the same over the entire

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length of a body, strain may be defined as:

ε=L f−Lο

Lο

Where:

Lο Is the initial

length

Lf Is the final length

Types of strain

1- Length strain

If matter its length L and stress effect on it and increase its length by L

strain =L/L

2- Volume strain

if stress change the volume of matter by V

strain= V/V

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3- Shear strain

If we affected by shear stress

strain =

Young Modulus is equal stress divided by strain.

Stress =F/A , strain = L/L

Y=σε= F /A

ΔL /LElastic limit

Strain is proportional to stress

This satisfies Hooke law.

This is true under elastic limit.

The sample reach to maximum stress by increase force doesn't cause extension and then the sample breakdown.

The relation between stress and strain is linear in elastic range

= Y this relation change out of elastic range and it will be exponential

σ=kεn

Importance of tensile test

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we perform this experiment for several reasons. The results of tensile tests are used in selecting materials for engineering applications.

When materials for engineering projects are procured, the engineer often must specify material property requirements to the manufacturer. After the material is received it is generally good practice, if not mandatory, to perform acceptance tests to verify the material properties before the materials are used. Therefore, it is important to understand which material properties are relevant and how those properties are obtained.

Tensile properties frequently are included in material specifications to ensure quality. Tensile properties often are measured during development of new materials and processes, so that different materials and processes can be compared.

Finally, tensile properties often are used to predict the behaviour of a material under forms of loading other than uniaxial tension.

Data

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F/ 0.4L/LL2010.033920.065530.097040.128550.159760.18

11170.2111280.2411390.3114100.33115110.36117120.39118130.42119140.45120150.48119160.51110170.54


Graphing Data

slope=Y =(97−55 )

(6−3 )×10−2×0. 4×10−4=35×106 N /m2

yield strength = 2 .775×104 N /m2

max. stress = 3×106 N /m2

breakdown stress = 2 .75×106 N /m2

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5- Internal frication

Objectives :-

Determine damping capacity

Determine young modulus

Tools and Equipment

Generator- magnetic field – oscilloscope – wires

Work

Put sample in magnetic field with certain length

Change the frequency from generator

Read the amplitude on oscilloscope

Draw relation between frequency on x-axis and amplitude on y-axis

Change the length of sample and repeat last steps

At every length increase frequency and determine the maximum vibrate and then we find young modulus.

Theory

Definition:

Internal fraction is the ability of materials of absorbing vibrations

We can determine internalk friction by three methods

1- resonance curve

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When appling magnetic field on metal slid that produce pulse on the slid so, the slid will vibrate.

When the frequency that applied on slid equal to the vibration of material itself the resonance occur and the amplitude will be maximum.

If applied frequency is less or great than resonance the frequency decrease and reached to zero.

The damping capacity is

Q−1= Δυυo

logarithmic decrement is max amplitude of consequence cycles for freely decaying vibration i.e.

δ=ln( An

An+1)

we can determine young modulus from relation

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A

O


Y= 4 π 2 ρk2 m4 ( L2 υo)

2

Data

At length =10cm

υO=17 Hz

Q−1=22 .9−10 .817

=0 . 711

At length = 15 cm

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A0.11.10.52.312.472.582.792.9

103.312.54154.5

17.24.9204.4

22.53.6253

27.52.7302.4

32.52.2352

37.51.9401.8

1.10.12.40.52.512.672.893.3103.712.54.115

417.53.4202.822.52.225

227.51.7301.532.51.4351.337.51.240


υo=14 .87 Hz

Q−1=21 .88−8 .514 . 87

=0 . 899

Logarithmic decrement is

δ= ln( 4 . 94 . 1 )=0 .178

Young Modulus

L21/2L4

15122254.420736

10151001050625

8.52072.2514160000

6253628290625

3289111614656

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Y= 4 π 2 ρk2 m4 ( L4 υo

2 )

slope=L4

1/υo2=Y

k 2m4

4 π 2 ρ

k=t

√12

1 .2207×104=Y(0 .072 )2(1 . 8)4

12×4 π2×7 . 89Y=8.3×108dyne /cm

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6- Spectrophotometer

Objectives

Determine refraction index

Determine thickness of sample

Determine absorption coefficient.

Determine gap energy.

Tools and Equipment

Spectrophotometer Device –sample slides –glass slide

Work

Turn on spectrophotometer and wait 15 min.

Input wavelength

Put glass slide its transmission 100%

Put sample slide and read transmission

Change wavelength and repeat last steps

Description of system

A spectrophotometer consists of two instruments :-

1- spectrometer for producing light of any selected color (wavelength),

2- photometer for measuring the intensity of light.

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The instruments are arranged so that liquid in a cuvette can be placed between the spectrometer beam and the photometer. The amount of light passing through the tube is measured by the photometer.

The photometer delivers a voltage signal to a display device, normally a galvanometer. The signal changes as the amount of light absorbed by the liquid changes.

If development of color is linked to the concentration of a substance in solution then that concentration can be measured by determining the extent of absorption of light at the appropriate wavelength. For example hemoglobin appears red because the hemoglobin absorbs blue and green light rays much more effectively than red. The degree of absorbance of blue or green light is proportional to the concentration of hemoglobin.

When monochromatic light (light of a specific wavelength) passes through a solution there is usually a quantitative relationship (Beer's law) between the solute concentration and the intensity of the transmitted light, that is,

where I sub 0 is the intensity of transmitted light using the pure solvent, I is the intensity of the transmitted light when the colored compound is added, c is concentration of the colored compound, l is the distance the light passes through the solution, and k is a constant. If the light path l is a constant, as is the case with a spectrophotometer, Beer's law may be written,

where k is a new constant and T is the transmittance of the solution. There is a logarithmic relationship between transmittance and the concentration of the colored compound. Thus,

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Design

Single beam spectrophotometer

There are two major classes of devices: single beam and double beam. A double beam spectrophotometer compares the light intensity between two light paths, one path containing a reference sample and the other the test sample. A single beam spectrophotometer measures the relative light intensity of the beam before and after a test sample is inserted. Although comparison measurements from double beam instruments are easier and more stable, single beam instruments can have a larger dynamic range and are optically simpler and more compact.

.In short, the sequence of events in a spectrophotometer is as follows:

1- The light source shines through a monochromatic.

2-An output wavelength is selected and beamed at the sample.

3-A fraction of the monochromatic light is transmitted through the sample and to the photo detector.

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http://en.wikipedia.org/wiki/File:Spetrophotometer-en.svg


Many spectrophotometers must be calibrated by a procedure known as "zeroing." The absorbency of a reference substance is set as a baseline value, so the absorbencies of all other substances are recorded relative to the initial "zeroed" substance. The spectrophotometer then displays % absorbency (the amount of light absorbed relative to the initial substance).

Theory

In solid state physics, a band gap, also called an energy gap or band gap, It is an energy range in a solid where no electron states can exist.

In graphs of the electronic band structure of solids, the band gap generally refers to the energy difference (in electron volts) between the top of the valence band and the bottom of the conduction band in insulators and semiconductors.

This is equivalent to the energy required to free an outer shell electron from its orbit about the nucleus to become a mobile charge carrier, able to move freely within the solid material.

In conductors, the two bands often overlap, so they may not have a band gap.

In semiconductors and insulators, electrons are confined to a number of bands of energy, and forbidden from other regions.

The term "band gap" refers to the energy difference between the top of the valence band and the bottom of the conduction band. Electrons are able to jump from one band to another. However, in order for an electron to jump from a valence band to a conduction band, it requires a specific minimum amount of energy for the transition. The required energy differs with different materials. Electrons can gain enough energy to jump to the conduction band by absorbing either a phonon (heat) or a photon (light).

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A semiconductor is a material with a small but nonzero band gap which behaves as an insulator at absolute zero but allows thermal excitation of electrons into its conduction band at temperatures which are below its melting point. In contrast, a material with a large band gap is an insulator. In conductors, the valence and conduction bands may overlap, so they may not have a band gap.

The conductivity of intrinsic semiconductors is strongly dependent on the band gap. The only available carriers for conduction are the electrons which have enough thermal energy to be excited across the band gap.

The distinction between semiconductors and insulators is a matter of convention. One approach is to think of semiconductors as a type of insulator with a narrow band gap. Insulators with a larger band gap, usually greater than 3 e.V are not considered semiconductors and generally do not exhibit semi-conductive behavior under practical conditions.

Electron mobility also plays a role in determining a material's informal classification.

The band gap energy of semiconductors tends to decrease with increasing temperature. When temperature increases, the amplitude of atomic vibrations increase, leading to larger inter atomic spacing. The interaction between the lattice phonons and the free electrons and holes will also affect the band gap to a smaller extent.

Mathematical review

refraction index is given by

n1=√m1+√m12+ng

2

n2=√m2+√m22+ng

2

where m1 and m2 is constant and given by

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m1=ng

2+1

2−

2 ng

T1min

2

m2=ng

2+1

2−

2 ng

T2min

2

where ng is refractive index of glass = 1.5

T1 , T2 are minimum transmission

One can get the thickness of sample from :

t=λ1 λ2

2 (n1 λ2−n2 λ1 )Transmission is given by

T=T oe−αt

take logarithm for both sides

ln T=lnTo−αt

So, the transmission coefficient is

α=1t

ln(T o

T )

Data

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T19320203402436023380274002842030440354603548022500275202854025560245802760030620276402466028680307002872026740207602178019800


T1 = 22 , T2 = 24

1 = 440 nm , 2 = 540 nm

m1=ng

2+1

2−

2 ng

t1min

2 =1 .6188

m2=ng

2+1

2−

2 ng

t2min

2 =1 .6198

n1=√m1+√m12−ng

2=1 .49248

n2=√m2+√m22−ng

2=1 .49369

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t=λ1 λ2

2(n1 λ2−n2 λ1)=798 .84 nm

α=1t

lnT o

T , T o=100

α 1=1798 . 84

ln10020

=2 . 01×10−3

α 2=1798. 84

ln10028

=1 . 5935×10−3

α 3=1798 .84

ln10030

=1 . 51×10−3

α 4=1798 . 84

ln10022

=1 .89×10−3

α 5=1798. 84

ln10027

=1 . 64×10−3

α 6=1798 .84

ln10024

=1. 78×10−3

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E1=hCλ1

=6. 62×10−34×3×108

340×10−9=5 . 83×10−19 J

E2=hCλ2

=6 .62×10−34×3×108

420×10−9=4 .72×10−19 J

E3=hCλ3

=6 .62×10−34×3×108

440×10−9=4 . 51×10−19 J

E4=hCλ4

=6 . 62×10−34×3×108

500×10−9=3 . 97×10−19 J

E5=hCλ5

=6 .62×10−34×3×108

520×10−9=3 . 82×10−19 J

E6=hCλ6

=6 . 62×10−34×3×108

580×10−9=3. 42×10−19 J

α 1 E1=2.01×10−3×5. 83×10−19=1 .18×10−22

α 2 E2=1 .5935×10−3×4 . 72×10−19=7 .53×10−22

α 2 E3=1 .51×10−3×4 . 51×10−19=6 .82×10−22

α 4 E4=1 .89×10−3×3 . 97×10−19=7 . 51×10−22

α 5 E5=1 .64×10−3×3 . 82×10−19=6 .26×10−22

α 6 E6=1 . 78×10−3×3 . 42×10−19=6 .1×10−22

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E×10−19(αE )2×10−43

5.831.384.725.674.514.653.975.643.823.923.423.71


7- Characteristic of thermistor

Objectives

study Characteristic of thermistor

determine temperature coefficient of resistance

Tools and equipment

heater – thermometer - oil – thermistor – multi-meter

thermistor

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used circuit

Work

Connect the last circuit.

Put thermistor in oil and put inside heater

Put thermometer inside oil.

Turn on the heater and raise temperature of it step by step.

Every five degree read the value of resistance.

Draw relation between T on x-axis and R on y-axis.

Theory

A thermistor is a type of resistor whose resistance varies significantly with temperature. The word is a portmanteau of thermal and resistor. Thermistors are widely used as inrush current limiters, temperature sensors, self-resetting over current protectors, and self-regulating heating elements.

Thermistors differ from resistance temperature detectors (RTD) in that the material used in a thermistor is generally a ceramic or polymer, while RTD use pure metals. The temperature response is also different;

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RTD are useful over larger temperature ranges, while Thermistors typically achieve a higher precision within a limited temperature range [usually −90 °C to 130 °C].

Assuming, as a first-order approximation, that the relationship between resistance and temperature is linear, then:

where

ΔR = change in resistance

ΔT = change in temperature

k = first-order temperature coefficient of resistance

Thermistors can be classified into two types, depending on the sign of k.

If k is positive, the resistance increases with increasing temperature, and the device is called a positive temperature coefficient (PTC) thermistor.

If k is negative, the resistance decreases with increasing temperature, and the device is called a negative temperature coefficient (NTC) thermistor.

Resistors that are not thermistors are designed to have a k as close to zero as possible(smallest possible k), so that their resistance remains nearly constant over a wide temperature range.

Instead of the temperature coefficient k, sometimes the temperature coefficient of resistance α (alpha) or αT is used. It is defined as

For example, for the common PT100 sensor, α = 0.00385 or 0.385 %/°C. This αT coefficient should not be confused with the α parameter below.

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In practice, the linear approximation (above) works only over a small temperature range. For accurate temperature measurements, the resistance/temperature curve of the device must be described in more detail. The Steinhart-Hart equation is a widely used third-order approximation:

where a, b and c are called the Steinhart-Hart parameters, and must be specified for each device. T is the temperature in Kelvin and R is the resistance in ohms. To give resistance as a function of temperature, the above can be rearranged into:

where

and

NTC thermistors can also be characterized with the B parameter equation,

where the temperatures are in Kelvin and R0 is the resistance at temperature T0 (usually 25 °C = 298.15 K). Solving for R yields:

or, alternatively,

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where .

This can be solved for the temperature:

The B-parameter equation can also be written as

.

This can be used to convert the function of resistance vs. temperature of a thermistor into a linear function of lnR vs. 1 / T. The average slope of this function will then yield an estimate of the value of the B parameter.

Applications

PTC thermistors can be used as current-limiting devices for circuit protection, as replacements for fuses. Current through the device causes a small amount of resistive heating. If the current is large enough to generate more heat than the device can lose to its surroundings, the device heats up, causing its resistance to increase, and therefore causing even more heating. This creates a self-reinforcing effect that drives the resistance upwards, reducing the current and voltage available to the device.

PTC thermistors are used as timers in the degaussing coil circuit of CRT displays and televisions. When the unit is initially switched on, current flows through the thermistor and degauss coil. The coil and thermistor are intentionally sized so that the current flow will heat the thermistor to the point that the degauss coil shuts off in under a second.

NTC thermistors are used as resistance thermometers in low-temperature measurements of the order of 10 K.

NTC thermistors can be used as inrush-current limiting devices in power supply circuits. They present a higher resistance initially

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which prevents large currents from flowing at turn-on, and then heat up and become much lower resistance to allow higher current flow during normal operation. These thermistors are usually much larger than measuring type thermistors, and are purposely designed for this application.

NTC thermistors are regularly used in automotive applications. For example, they monitor things like coolant temperature and/or oil temperature inside the engine and provide data to the ECU and, indirectly, to the dashboard. They can be also used to monitor temperature of an incubator.

Thermistors are also commonly used in modern digital thermostats and to monitor the temperature of battery packs while charging.

Data

TRlnR1/T27109.50.0370374.6959253099.10.0333334.5961293580.50.0285714.38825740660.0254.1896554557.70.0222224.0552575048.40.023.87955540.40.0181823.6988360330.0166673.4965086527.30.0153853.3068877022.70.0142863.1223657518.80.0133332.9338578015.80.01252.760018513.30.0117652.587764

Graph

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8- Temperature Coefficient of Resistance of metals TCR

Objectives

Study relation between resistance and temperature

Determine Thermal Coefficient of Resistance

Tools and equipment

Heater – thermometer – oil – ohmmeter

Work

Connect sample with ohmmeter.

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Put sample in oil and pu t them inside Heater.

Put thermometer inside oil .

Turn on heater slowly.

Read resistance every 5 degree.

Used circuit

Theory

Resistance of metals increase with increasing temperature due to lattice vibrations in metals

Such that

Rt=Ro(1+αT+ βT2+γT 3 )

where

Rt is metal resistance at temperature t

R0 is metal resistance at temperature 0

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Heater


In medium temperature range we note that :-

and is very small compared with

So the equation will be

Rt=Ro (1+αT )such that

is temperature coefficient of resistance

that defined as the increasing of resistance when raising temperature by 1 C

observation

when we increase temperature the resistance increase

at room temperature (22 C) resistance is 125.5

when temperature reached to 90 C the resistance was 159

DataRT

125.52212625

126.53012835

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130401324513550

137.855140601436514670

149.575152.5801568515990

Graph

α= slopeRo

= 0 . 6001114. 609803

=5×10−3 Co −1

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9- Magnetic susceptibility

Objectives

Determine magnetic susceptibility for ferromagnetic material.

Tools and equipment

Electric magnet – glass tube – sensitive scale.

Work

Put tube at half distance between the two magnetic poles.

Input direct current for electric magnet produce magnetic field that applied on sample.

Change current and every time read magnetic force.

Theory

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Magnetic susceptibility is the ability of material for magnetization when external magnetic field applied.

Magnetic susceptibility is depend on the magnetic properties of material

χ= μH

such that :-

is magnetic dipole moment. , H is intensity of external magnetic field.

The materials divided due to magnetic properties as following :

1- Diamagnetic materials

The resultant magnetic dipole moment equal to zero

Magnetic susceptibility is (–ve ).

Magnetic susceptibility and temperature are independent each other.

2- Paramagnetic

The resultant magnetic dipole moment is greater than zero

Magnetic susceptibility is (+ve) greater than zero

Magnetic susceptibility is inversely proportional to temperature obey Curie law

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χm=CT

C is Curie constant

3- ferromagnetic material

magnetic susceptibility is large and depend on spin that spin is parallel .

the atoms reoriented with the direction of external magnetic field.

when magnetic field is removed these material keep magnetization due to these materials have permanent dipole moment.

The magnetic field just reoriented atoms in the same direction.

So these materials have hysteresis loop.

4- Anti-ferromagnetic materials

magnetic susceptibility is (+ ve) and depend on spin that is anti-parallel.

Obey Curie law.

these materials have hysteresis loop.

The magnetic force that acting on material is given by

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F z=χ2− χ1

2 (∂H x2

∂ z+∂H y

2

∂ z+∂H z

2

∂ z )dv

F y=χ 2− χ 1

2 (∂ H x2

∂ y+∂H y

2

∂ y+∂H z

2

∂ y )dv

Fx=χ2− χ1

2 (∂H x2

∂ x+∂ H y

2

∂ x+∂H z

2

∂ x )dv→(1)

where 1,2 are magnetic susceptibility for material and surrounding medium respectively.

But Hz and Hx are very small

So, we can neglect Fz and Fy .

Then equation (1) will be

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Fx=χ2− χ1

2 (∂H y2

∂ x )dv

but dv=Adx (A is area )

Fx=χ2− χ1

2 (∂H y2

∂ x )Adx .

total force is

F=∫Ho

H

Fx=∫H o

H χ2− χ1

2AdH y

2

=χ 2− χ 1

2A (H2−Ho

2 )

but χ2>> χ1 , H >> Ho

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∴F=χ 2

2AH 2

F=Δm . g=χ2

2AH 2

butMAl

=ρ

∴ χ=2 Δm . gl ρ

MH 2

χ=2 glM (Δm

H 2 )we can calculate H from

H=2 πn10 r

I

n is no. Of cycles =1500 , r is distance between two magnets = 3.7 cm.

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Data

IIH*2 ×106mom

00021.50

0.20.040.5551652210.5

0.40.160.2220660820.51

0.60.360.49964868201.5

0.80.640.8882643219.52

111.38791174.5

1.21.443.0670811.510

1.41.963.187921110.5

1.62.563.553061011.5

1.83.244.49684912.5

245.551658.513

2.24.846.71757.514

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χ=3. 27×10−6 cm4 /s2 A2

10- Hysteresis Loop

Objectives

Study hysteresis loop

Determine reverse saturation current

Tools and Equipments

Oscilloscope – capacitors – resistors – some wires – inductance – DC battery – voltmeter

Used circuit

R12-3

C1 100n

R137k

L1500

L21000

IOSC 1kHz

V1 6V

Work

Connect the pervious circuit.

Change voltage from DC battery and every time read volt.

Draw the curve from oscilloscope.

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Calculate the area of curve and draw the relation between A on x-axis and I on y-axis.

Put different materials inside coil and observe its hystersis loop.

Theory

A great deal of information can be learned about the magnetic properties of a material by studying its hysteresis loop. A Hysteresis loop shows the relationship between the induced magnetic flux density (B) and the magnetizing force (H). It is often referred to as the B-H loop.

An example hysteresis loop is shown below.

The loop is generated by measuring the magnetic flux of a ferromagnetic material while the magnetizing force is changed.

A ferromagnetic material that has never been previously magnetized or has been thoroughly demagnetized will follow the dashed line as H is

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increased. As the line demonstrates, the greater the amount of current applied (H+), the stronger the magnetic field in the component (B+). At point "a" almost all of the magnetic domains are aligned and an additional increase in the magnetizing force will produce very little increase in magnetic flux.

The material has reached the point of magnetic saturation. When H is reduced to zero, the curve will move from point "a" to point "b." At this point, it can be seen that some magnetic flux remains in the material even though the magnetizing force is zero. This is referred to as the point of retentively on the graph and indicates the level of residual magnetism in the material. (Some of the magnetic domains remain aligned but some have lost their alignment.)

As the magnetizing force is reversed, the curve moves to point "c", where the flux has been reduced to zero. This is called the point of coercivity on the curve. (The reversed magnetizing force has flipped enough of the domains so that the net flux within the material is zero.)

The force required to remove the residual magnetism from the material is called the coercive force or coercively of the material.

As the magnetizing force is increased in the negative direction, the material will again become magnetically saturated but in the opposite direction (point "d"). Reducing H to zero brings the curve to point "e." It will have a level of residual magnetism equal to that achieved in the other direction. Increasing H back in the positive direction will return B to zero.

Notice that the curve did not return to the origin of the graph because some force is required to remove the residual magnetism.

The curve will take a different path from point "f" back to the saturation point where it with complete the loop.

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From the hysteresis loop, a number of primary magnetic properties of a material can be determined.

Retentively - A measure of the residual flux density corresponding to the saturation induction of a magnetic material. In other words, it is a material's ability to retain a certain amount of residual magnetic field when the magnetizing force is removed after achieving saturation. (The value of B at point b on the hysteresis curve.)

Residual Magnetism or Residual Flux - the magnetic flux density that remains in a material when the magnetizing force is zero. Note that residual magnetism and retentivity are the same when the material has been magnetized to the saturation point. However, the level of residual magnetism may be lower than the retentivity value when the magnetizing force did not reach the saturation level.

Coercive Force - The amount of reverse magnetic field which must be applied to a magnetic material to make the magnetic flux return to zero. (The value of H at point c on the hysteresis curve.)

Permeability, - A property of a material that describes the ease with which a magnetic flux is established in the component.

Reluctance - Is the opposition that a ferromagnetic material shows to the establishment of a magnetic field. Reluctance is analogous to the resistance in an electrical circuit.

We summarize speaking in the following :

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The area of hystersis loop divided to three regions :-

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- rectangle (its A = length x width)

- tow triangle (its A = 1/2 base length x height)

Observation

The area of hysteresis loop increase with increasing voltage.

When putting stales inside coil there is no change.

When putting steel inside coil the area increase something .

When putting iron inside coil the area increase sharply.

Data

IA21.342.262.72103.7125.15145.6

Graph

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