Monday, June 10, 2013

Modern Semiconductor Device

Introduction to Modern Semiconductor Device

Electronic devices, diodes, transistors .. etc are made form semiconductors.The group of closely lying energy levels corresponding to an orbital is called an energy band. The band that contains valence electrons or the highest completely filled band or partially filled band of a solid is called valence band.The lowest unfilled or empty band of a solid is called conduction band. The energy gap between the valence and conduction bands i.e., the difference between the lowest energy of the conduction band and the highest energy of the valence band is called forbidden band or forbidden gap or energy gap. If the conduction and valence bands overlap , the solid is called conductor.  If the conduction and valence bands are separated by an energy gap of greater than 5 eV or the forbidden band width is greater than 5 eV, the solid is an insulator. If the forbidden band width is about 1 eV, the solid is a semiconductor. A pure semiconductor is called intrinsic semiconductor. Wen a semiconductor contains an impurity then the semiconductor is called an extrinsic semiconductor. It increases the conductivity of a semiconductor.Adding an impurity to a semiconductor is called doping. Extrinsic semiconductors are of two types (i) n - type semiconductor and (ii) p - type semiconductor.

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Modern Semiconductor devices

Diode :  Diode is a device with two electrodes. A p-n junction diode is a two terminal device made up of a semiconductor crystal. It has two terminals which act as electrodes. A diode is said to be forward - biased, when the p-side of the diode is connected to the positive terminal of a battery and the n-side of the diode is connected to the negative terminal of the battery. A diode is said to be reverse - biased , when the p-side of the diode is connected to the negative terminal of a battery and the n-side of the diode is connected to the positive terminal of the battery.

Rectifier:  Rectifier is a device that converts alternating current (ac) to direct current (dc). In a half wave rectifier, the output current which is dc flows for only half of the input ac. The maximum efficiency of a half wave rectifier is 40.6%. In a full wave rectifier, the output current which is dc flows during both the halves of the input ac. The maximum efficiency of a full wave rectifier is 81.2%.

Zener diode : Zener diode is a special type of diode that allows current in the forward direction lika a p - n junction diode but also in the reverse direction fi the voltage is larger than the rated break down voltage or Zener voltage without any damage. Zener diode is used as a voltage regulator.

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Modern Semiconductor devices (continued)


Transistor : A transistor is a three terminal device . Its three parts are (1)emitter(E), (ii) base (B) and (iii) collector (C). The emitter of a transistor is heavily doped and is of intermediate size. The base of a transistor is least doped and is of least size. The collector of a transistor is of intermediate doping level and is of largest size. The two types of a transistor are (i) n - p -n transistor and (ii) p - n - p transistor. The three configurations of a transistor are (i) common - emitter (CE) configuration,  (ii) common - base (CB) configuration and (III) common -collector (CC) configuration. A transistor is used as an amplifier.

logic gate :  A logic gate is an electronic circuit which performs a particular logical function. Logic gates are of different types depending upon the logical function performed by the gate. The different types are (i) AND gate, (ii) OR gate , (iii) NOT gate , (iv) NOR gate and (v) NAND gate.

Byproducts of Coal Burning

Introduction to by products of coal burning

Coal is an extremely important fuel and will always remain so. About 23% of primary energy needs are met by coal and 39% of electricity generation takes place from coal. Nearly 70% of world steel production depends on coal feedstock. Coal is the world's most abundant and widely distributed fossil fuel source. The International Energy Agency expects a 43% increase in its use from 2000 to 2020.

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Coal burning produces many by products some of which are useful and others harmful as mentioned:

Carbon dioxide

Burning coal produces about 9 billion tones of carbon dioxide each year which is released to the atmosphere, about 70% of this being used for power generation.  The copious amounts of carbon dioxide that coal fired power stations push into the air – far greater amounts per unit of electrical energy than any other form of electrical generation. However, the coal pollution is not limited to carbon dioxide, which warms up our planet. There are other dangerous by products of coal burning.

Of course the actual types of by product depend on the nature and quality of the coal that is burnt, and its energy content


By products of coal burning : Nitrogen dioxide and sulphur dioxide , Soot


Nitrogen dioxide and sulphur dioxide

Most coal burning releases nitrogen dioxide and sulphur dioxide. Both chemicals make acid rain, which in turn is making the oceans more acidic. It is indicative of the energy companies’ attitude to pollution that although it has been possible to reduce the emissions of sulphur dioxide from coal by 90% for many years, it has taken a European Union Directive about air quality to force the installation of Flue Gas Desulphurisation at Aberthaw Power Station in South Wales.

Soot

All coal burning releases soot. Many people die from inhaling soot each year – the United Nations place the figure at 40,000.Hence, soot is very harmful to humans if taken in at large amounts.

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By products of coal burning : Ash and clinker , Mercury


Ash and clinker

All coal burning creates ash and clinker. The ash often contains traces of heavy metals such as cadmium, lead mercury and arsenic. The electricity generators simply dump the ash and clinker, burying it in landfill. The ash and clinker has about as much use as those slag heaps, now largely grassed over, that surrounded coal mines – both ugly and dangerous. It has no use, so it is dumped.

Mercury

Most coal burning release mercury into the atmosphere. Some species of fish are very good at absorbing mercury and that makes eating those species dangerous for the very young and for pregnant women, as I have explained elsewhere on these posts.

Of course in release these and other by products, the power station operators are simply trying to maximise their profits from power generation because environmentally friendly expenses stand in their way of profits. They sell their electricity to us, and virtually all of us are more interested in buying the product as cheaply as we can, regardless of the environmental consequences.

Study Definition of E

Introduction to study definition of e:
The charge is the inherent property of the matter. As the two substances rubbed with each other some of the electrons are transferred to one body to the another. The body, which gains the electrons, have positive charge and the other which lose the electrons get the negative charge. The charge of an electron is the elementary charge and denoted by the e. We cannot reduce the charge as one third of electron or any other quantity, because the charge of an electron is elementary.

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Study definition of e:


The electric charge is the basic property of the matter due to which the electrostatic force comes into play. The charges are of the two types: positive and negative charge. The S.I. unit of charge is coulomb and the other units are esu, emu, stat coulomb etc. The electric charge is conserved and quantized. The electric charge does not depend on the velocity of that charged particle if it is moving. The experimental value of the elementary charge e is 1.602176487 × 10-19 Coulomb in S.I. units and in CGS units the value of the elementary charge is 4.80320427 × 10-10 stat coulomb. For the sake of the convenience, the charge of the electron is considered as -1 and the charge of the proton is + 1. In the terms of the Avogadro constant and the Faraday constant the elementary charge is the ratio of the Faraday’s constant and the Avogadro’s constant.

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Experimental measurements of the elementary charge:


We can find the value of the elementary charge by the Millikan’s oil drop experiment. In the experiment a small drop of a oil falls in the electric field. The force of gravity and the viscosity be deducted by the electric field force and to get the value of the elementary charge. We can produce the electric charge on any material by rubbing it with another material; this is known by the conduction. The other method is called the induction in which the charge is induced on the body by the charge of the another body. In case of induction, the charges on the two bodies are of opposite nature but in the conduction, the charge is of the same nature.

Unified Field Theory for Dummies

Physics, a unified field theory is a type of field theory that allows all that is usually thought of as fundamental forces and elementary particles to be written in terms of a single field. There is no accepted unified field theory. It remains an open line of research. The term was coined by Einstein who attempted to unify the general theory of relativity with electromagnetism, hoping to recover an approximation for quantum theory. A "theory of everything" is closely related to unified field theory, but differs by not requiring the basis of nature to be fields, and also attempts to explain all physical constants of nature.

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This article describes unified field theory as it is currently understood in connection with quantum theory. Earlier attempts based on classical physics are described in the article on classical unified field theories.

There may be no a prior reason why the correct description of nature has to be a unified field theory; however, this goal has led to a great deal of progress in modern theoretical physics and continues to motivate research. Unified field theory is only one possible approach to unification of physics

The first successful (classical) unified field theory was developed by James Clerk Maxwell. In 1820 Hans Christian Ørsted discovered that electric currents exerted forces on magnets, while in 1831, Michael Faraday made the observation that time-varying magnetic fields could induce electric currents. Until then, electricity and magnetism had been thought of as unrelated phenomena. In 1864, Maxwell published his famous paper on a dynamical theory of the electromagnetic field. This was the first example of a theory that was able to encompass previous separate field theories (namely electricity and magnetism) to provide a unifying theory of electromagnetism. Later, in his theory of special relativity, Albert Einstein was able to explain the unity of electricity and magnetism as a consequence of the unification of space and time into an entity we now call spacetime.

In 1921 Theodor Kaluza extended General Relativity to five dimensions and in 1926 Oscar Klein proposed that the fourth spatial dimension be curled up (or compactified) into a small, unobserved circle. This was dubbed Kaluza-Klein theory. It was quickly noticed that this extra spatial direction gave rise to an additional force similar to electricity and magnetism. This was pursued as the basis for some of Albert Einstein's later unsuccessful attempts at a unified field theory. Einstein and others pursued various non-quantum approaches to unifying these forces; however as quantum theory became generally accepted as fundamental, most physicists came to view all such theories as doomed to failure.

Friday, June 7, 2013

Hydrogen Fuel Cell Science

Introduction to hydrogen fuel cell science:

The first fuel was conceived by a Welsh judge, inventor Sir William Robert in 1839. In the occurrence of an electrolyte, he mixed hydrogen and oxygen to produce electricity and water. Later on, this invention was known as fuel cell but it didn’t produce enough electricity which is to be used.

Afterwards, in 1889, Ludwig Mond coined the term ‘fuel’ who attempted building a functioning fuel cell with air and industrial coal gas.


Functioning of hydrogen fuel cell:


Hydrogen fuel cells generate electricity quickly and efficiently, without pollution.

A fuel cell is a conversion device of electrochemical energy. It converts the chemicals such as hydrogen and oxygen into water. In the whole process, it produces electricity. When we use fuel cell, chemicals flow constantly into the cell so it never goes dead. As the chemicals flow in cell, electricity flows out of the cell. Most of the fuel cell use hydrogen and oxygen as chemicals.


Types of fuel cells in addition to hydrogen fuel cell:


The fuel cell has the competition with various energy conversion devices which includes the gas turbine in our city’s power plant, the gasoline engine in our car and the most important the battery in our laptops. A fuel cell gives a direct current voltage that is used to power motors, lights and any number of electrical appliances. There are many types of fuel cells, each use different chemistry. For example, polymer exchange membrane fuel cell, solid oxide fuel cell, alkaline fuel cell, and molten carbonate fuel cell, phosphoric acid fuel cell, and direct methanol fuel cell, etc.


Efficiency of hydrogen fuel cell:


The primary goal of fuel cell is the pollution reduction. Fuel cell has capability to be up to 80% efficient, if it is powered with pure hydrogen. It means it converts 80% of the hydrogen energy into electrical energy. This electrical energy is changed into mechanical work by electric motor and inverter.


Disadvantages of hydrogen fuel cells:

Most of the fuel cell components are very expensive.
In general, fuel cells are slightly bigger than other batteries and engines.
The refueling and starting time of this cell vehicles are very longer.
This technology is not fully generated.

Thursday, June 6, 2013

Science Definition of Matter

Introduction to science definition of matter:
If we hold a glass sheet in our hand and look at it, the sheet appears to be a continuous one. In case it falls due to accident or by our negligence, what will happen? It will immediately break in to very small or tiny pieces. What does it show? The fine pieces of glass indicate that the sheet is made up of particles. In fact, every matter is made up of certain particles which differ in shape, size and nature from other type of matter.

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Important characteristics of nature of matter


The important characteristics of the particulate nature of matter may be summed up as follows:

Every matter is made up of particles.
The particles constituting a matter are very small in size.
The particles have empty or vacant spaces in them known as inter particle spaces.
Particles are not stationary and are in a state of motion.
Attractive forces are present in the particles of a substance. These are called inter particle forces.
The particle motion increases with the rise in temperature.

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Explanation to science definition of matter

Hence, Anything or everything which occupies space and has mass, is known as matter. According to ancient Greeks and Indian Philosophers, matter is made from five constituents namely air, earth, water, fire and sky. Matter has two ways of classification. These are physical and chemical classification. Matter is made up of particles which are characterized by shape, size and mass. Inter particle spaces are present in all types of matter. Their size and number can vary from one matter to the other. Matter is always seen as an aggregate of small or tiny particles which cannot be seen individually by naked eye.  Particles present in a matter are in a state of motion. It is least in the solid state and maximum in the gaseous state. Inter particle attraction depends on the physical state of the matter. Particle motion generally increases with the rise in temperature. Thus,Matter has many definitions, but the most common is that it is any substance which has mass and occupies space. All physical objects are composed of matter, in the form of atoms, which are in turn composed of protons, neutrons, and electrons.

Prepare Saturated Solution

Introduction of Prepare saturated solution:

When a solute is added in to the solvent a solution is prepare. A more amount is solute is added in to this solution, it will dissolve. After continuously added solute in to the solution, a stage is come at which no more amount of solute is added, and we prepare saturated solution. Saturated solution is that solution in which no more amount of solute are added under normal condition of temperature and pressure. Unsaturated solution is that solution in which more amount of solute can be added to prepare a saturated solution under normal condition of temperature and pressure.

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Properties of prepare saturated solution:


A saturated solution dissolves only a limited amount of solute.

More amount of solute can be added to a saturated solution on increasing the temperature of solution. It means a prepare saturated solution converts into the unsaturated one on increasing the temperature. After some period of time, dissolved solute of prepares saturated solution crystallize.

A prepare saturated solution gives the idea about the solubility of the dissolved solute in a particular solvent under normal condition of temperature and pressure.

Dissolved solute of a prepare saturated solution precipitate under shearing conditions.

A saturated solution is highly viscous in nature and has very high surface tension.


Preparation of saturated solutions:


Sugar’s saturated solution:

To prepare saturated solution dissolves, sugar in water, take the 100 ml of water to a beaker. To this beaker, add the 1 g of sugar. And mix the solution continuously. This gives a sugar solution. To this sugar solution, further, add 1 g of sugar, and continuously stir it. Again add the more and more amount of sugar continuously to this and stir it, until no more sugar is dissolved. Filter this sugar solution. This gives a prepare saturated solution of sugar in water this saturated solution dissolves maximum amount of solute that it can be dissolved under normal condition of temperature and pressure. Count the total amount of sugar added to the 100 ml of water. And calculate the solubility of sugar in water under normal condition of temperature and pressure by dividing the total amount of sugar added to the total volume of water.