Basic Electronics Essay Example for Free

Basic Electronics Essay The p-n junction is a homojunction between a p-type and an n-type semiconductor. It acts as a diode, which can serve in electronics as a rectifier, logic gate, voltage regulator (Zener diode), switching or tuner (varactor diode); and in optoelectronics as a light-emitting diode (LED), laser diode, photodetector, or solar cell. In a relatively simplified view of semiconductor materials, we can envision a semiconductor as having two types of charge carriers-holes and free electrons which travel in opposite directions when the semiconductor is subject to an external electric field, giving rise to a net flow of current in the direction of the electric field. Figure 1 illustrates the concept. A p-n junction consists of a p-type and n-type section of the same semiconductor materials in metallurgical contact. The p-type region has an abundance of holes (majority carriers) and a few mobile electrons (minority carriers); the n-type region has an abundance of mobile electrons and a few holes (Fig. 2). Both charge carriers are in continuous random thermal motion in all directions. Fig. 2. Energy levels and carrier concentrations for a p-type and n-type semiconductor before contact. 1 When a section of p-type material and a section of n-type material are brought in contact to form a pn junction, a number of interesting properties arise. The pn junction forms the basis of the semiconductor diode. Electrons and holes diffuse from areas of high concentration toward areas of low concentration. Thus, electrons diffuse from the n-region to the p-region. , leaving behind positively charged ionized donor atoms. In the p-region the electrons recombine with the abundant holes. Similarly, holes diffuse from the p-region into the n-region, leaving behind negatively charged ionized acceptor atoms. In the n-region the holes recombine with the abundant mobile electrons. This diffusion process does not continue indefinitely, however, because it causes a disruption of the charge balance in the two regions. As a result, a narrow region on both sides of the junction becomes nearly depleted of the mobile charge carriers. This region is called the depletion layer. It contains only the fixed charges (positive ions on the n-side and negative ions on the p-side). The thickness of the depletion layer in each region is inversely proportional to the concentration of dopants in the region. The net effect is that, the depletion region sees a separation of charge, giving rise to an electric field pointing from the n side to the p side. The fixed charges create an electric field in the depletion layer that points from the n-side towards the p-side of the junction. The charge separation therefore causes a contact potential (also known as built-in potential) to exist at the junction. This built-in field obstructs the diffusion of further mobile carriers through the junction region. An equilibrium condition is established that results in a net contact potential difference Vo between the two sides of the depletion layer, with the n-side exhibiting a higher potential than the p-side. This contact potential is typically on the order of a few tenths of a volt and depends on the material (about 0. 5 to 0. 7 V for silicon). The built-in potential provides a lower potential energy for an electron on the n-side relative to the p-side. As a result, the energy bands bend as shown in Fig. 3. In thermal equilibrium there is only a single Fermi function for the entire structure so that the Fermi levels in the p- and the n-regions must align. No net current flows across the junction. The currents associated with the diffusion and built-in field (drift current) cancel for both the electrons and holes. Fig. 3. A p-n junction in the Thermal equilibrium at T gt; 0? K. The depletion-layer, energy-band diagram, and concentrations (on a logarithmic scale) of the mobile electrons n(x) and holes p(x) are shown as a functions of the position x. The built-in potential difference V corresponds to the energy eV where e is the electron charge. 0 0 2 The Biased p-n Junction An externally applied potential will alter the potential difference between the p- and n-regions. This in turn will modify the flow of majority carriers, so that the junction can be used as a â€Å"gate†. If the junction is forward biased by applying a positive voltage V to the p-region (Fig. 4), its potential is increased with respect to the n-region, so that an electric field is produced in a direction opposite to that of the built-in field. The presence of the external bias voltage causes a departure from equilibrium and a misalignment of the Fermi levels in the p- and n-regions, as well as in the depletion layer. The presence of the two Fermi levels in the depletion layer, Efc and Efv represents a state of quasi-equilibrium. Fig. 4. Energy band diagram and carrier concentrations for a forward-biased p-n junction. In effect, then, if one were to connect the two terminals of the p-n junction to form a closed circuit, two currents would be present. First, a small current, called reverse saturation current, is, exists because of the presence of the contact potential and the associated electric field. In addition, it also happens that holes and free electrons with sufficient thermal energy can cross the junction. This current across the junction flows opposite to the reverse saturation current and is called diffusion current. Of course, if a hole from the p side enters, it is quite likely that it will quickly recombine with one of the n-type carriers on the n side. (Fig. 4) The net effect of the forward bias is to reduce the height of the potential-energy hill by an amount eV. The majority carrier current turns out to increase by an exponential factor exp(eV/kT). So that the net current becomes i = isexp(eV/kT) – is, where is is nearly a constant. The excess majority carrier holes and electrons that enter the n and p regions, respectively, become minority carriers and recombine with the local majority carriers. To explain the mechanism of reverse conduction, one needs to visualize the phenomenon of avalanche breakdown. When a very large negative bias is applied to the p-n junction, sufficient energy is imparted to charge carriers that reverse current can flow, well beyond the normal reverse, saturation current. In addition, because of the large electric field, electrons are energized to such levels that if they collide with other charge carriers at a lower energy level, some of their energy is transferred to the carriers with low energy, 4 and these can now contribute to the reverse conduction process, as well. This process is called impact ionization. Now, these new carriers may also have enough energy to energize other lowenergy electrons by impact ionization, so that once a sufficiently high reverse bias is provided, this process of conduction takes place very much like an avalanche: a single electron can ionize several others. Fig. 6. The reverse breakdown region The phenomenon of Zener breakdown is related to avalanche breakdown. It is usually achieved by means of heavily doped regions in the neighbourhood of the metal-semiconductor junction (the ohmic contact) . The high density of charge carriers provides the means for a substantial reverse breakdown current to be sustained at a much lower specific voltage than normal diode, at a nearly constant reverse bias known as the Zener voltage, Vz. This phenomenon is very useful in applications where one would like to hold some load voltage constant for example, in voltage regulators. The response time of a p-n junction to a dynamic (ac) applied voltage is determined by solving the set of differential equations governing the processes of electrons and hole diffusion, drift (under the influence of the built-in and external electric fields), and recombination. These effects are important for determining the speed at which the diode can be operated. They may be conveniently modeled by two capacitances, a junction capacitance and diffusion capacitance, in parallel with an ideal diode. The junction capacitance for the time necessary to change the fixed positive and negative charges stored in the depletion layer when the applied voltage changes. The thickness l of the depletion layer turns out to be proportional to v(Vo-V); it therefore increases under the reverse-bias conditions (negative V) and decreases under the forward-bias conditions (positive V). The junction capacitance C=?A/l (where A is the area of the junction) is therefore inversely proportional to v(VoV). The junction capacitance of a reverse-biased diode is smaller (and the RC response time is therefore shorter) than that of a forward-biased diode. The dependence of C on V is used to make voltage-variable capacitors (varactors). 5 Experiment l(a) : i-v characteristics of a semiconductor diode Procedure Connect the diode according to the circuit diagram as shown in Fig. 8. Fig 8 Vary the voltage V on the power supply between 0-30V. Alternately, the second concept is that the blocking action of an inductor stops the a. c. portion while the d. c. portion passes without much attenuation. Note: For filtering, large capacitance (hundreds to tens of hundreds microfarad) is needed. These are generally electrolytic capacitors, which consist of a repeating sandwich of aluminum sheets and a conducting paste, rolled into a cylinder for miminmun size. The aluminum sheets are polarized to form thin layers of aluminum oxide, a dielectric insulating material. The thinner the the dielectric the higher the capacitance will be.

The Old Man And The Sea Compared To Shipwrecked Sailor :: essays research papers

The Old Man and the Sea compared to â€Å"Shipwrecked Sailor† In the stories, The Old Man and the Sea by Ernest Hemmingway and â€Å"Shipwrecked Sailor† by Gabriel Garcia Marques, there are so many similarities, like their losses and their love for the creatures of the sea, that it its eerie. Although, there are many similarities, there are also some differences, such as the main characters’ love for the creatures of the sea. There are more similarities in these stories than differences, in my opinion.   Ã‚  Ã‚  Ã‚  Ã‚  A difference between Santiago in The Old Man and the Sea and the sailor in â€Å"Shipwrecked Sailor† is their knowledge of the sea. Santiago is expressed well as a fecund and resourceful old fisherman of the sea. This is prodigiously expressed when Santiago, †Hooked a patch of yellow Gulf weed with the gaff as they passed and shook it so that the small shrimps that were in it fell onto the planking of the skiff† (Hemmingway p.98). This is the act of a very intellectual and experienced fisherman. Unlike Santiago, the sailor in â€Å"Shipwrecked Sailor† is rather ignorant. Although, this is excused because the man hadn’t the experience at sea that Santiago had. His imbecility is shown when he, â€Å"Lay down at the side of the raft and took a few swallows of seawater† (Marques p.45). This was a rather fatuous action, because the salt dries the body and retains water. That action proves that he is not sea-worthy. So, Santiago i s the more experienced seaman of the two.   Ã‚  Ã‚  Ã‚  Ã‚  A similarity between The Old Man and the Sea and â€Å"Shipwrecked Sailor† was their losses. In the â€Å"Shipwrecked Sailor†, â€Å"The sharks had made off with my prey† (Marques p.44). This event marked the loss of the man’s food supply. It wasn’t a very crucial part of the story, because the man had earlier devoured some raw meat, which had satiated him. In The Old Man and the Sea, â€Å"He did not want to look at the fish. He knew half of him had been destroyed† (Hemmingway p.144). This was a very similar method of loss, which the shipwrecked sailor had faced. This was a tragic loss and abasement to both Santiago and his pride. He was tenacious and worked so hard to obtain the fish, only to have it taken away by sharks. The old man lost the fish, even though he fought valiantly to fend off the attacking sharks.

The Competitive Advantage of Nations

WHAT IS THE DIAMOND MODEL? DESCRIPTION The Diamond Model of Michael Porter for the competitive advantage of Nations offers a model that can help understand the comparative position of a nation in global competition. The model can also be used for major geographic regions. TRADITIONAL COUNTRY ADVANTAGES Traditionally, economic theory mentions the following factors for comparative advantage for regions or countries: 1. Land 2. Location 3. Natural resources (minerals, energy) 4. Labor, and 5. Local population size. Because these 5 factors can hardly be influenced, this fits in a rather passive (inherited) view regarding national economic opportunity. CLUSTERS Porter says that sustained industrial growth has hardly ever been built on above mentioned basic inherited factors. Abundance of such factors may actually undermine competitive advantage! He introduces a concept called â€Å"clusters† or groups of interconnected firms, suppliers, related industries, and institutions, that arise in certain locations. These clusters are geographic concentrations of interconnected companies, specialized suppliers, service providers, and associated institutions in a particular field. They grow on locations where enough resources and competences amass and reach a critical threshold, giving it a key position in a given economic branch of activity, with a decisive sustainable competitive advantage over others places, or even a world supremacy in that field. Porter says clusters can influence competition in three ways: †¢They can increase the productivity of the companies in the cluster. They can drive innovation in the field. †¢They can stimulate new businesses in the field. Some well-known examples of Clusters are USA/Silicon Valley (computers), Netherlands/Rotterdam (logistics), India/Bangalore (software outsourcing), USA/Hollywood (movies), France/Paris (fashion). According to Porter, as a rule competitive advantage of nations is the outcome of 4 interlinked advanced factors and activities in and between companies in these clusters. These can be influenced in a pro-active way by government. INTERLINKED ADVANCED FACTORS FOR COMPETITIVE ADVANTAGE 1. The Strategy, Structure and Rivalry of Firms. The world is dominated by dynamic conditions. Direct competition impels firms to work for increases in productivity and innovation. 2. Demand Conditions. If the customers in an economy are very demanding, the pressure facing firms to constantly improve their competitiveness via innovative products, through high quality, etc, will be greater. 3. Related Supporting Industries. Spatial proximity of upstream or downstream industries facilitates the exchange of information and promotes a continuous exchange of ideas and innovations. 4. Factor Conditions. Contrary to conventional wisdom, Porter argues that the â€Å"key† factors of production (or specialized factors) are created, not inherited. Specialized factors of production are skilled labor, capital and infrastructure. â€Å"Non-key† factors or general use factors, such as unskilled labor and raw materials, can be obtained by any company and, hence, do not generate sustained competitive advantage. However, specialized factors involve heavy, sustained investment. They are more difficult to duplicate. This creates a competitive advantage, because if other firms cannot easily duplicate these factors, they are valuable. THE ROLE OF GOVERNMENT IN THE DIAMOND MODEL OF PORTER The role of government in the Diamond Model of Porter is to act as a catalyst and challenger; it is to encourage – or even push – companies to raise their aspirations and move to higher levels of competitive performance. They must encourage companies to raise their performance, to stimulate early demand for advanced products, to focus on specialized factor creation and to stimulate local rivalry by limiting direct cooperation and enforcing anti-trust regulations. THE COMPETITIVE ADVANTAGE OF NATIONS Porter introduced this model in his book: â€Å"The Competitive Advantage of Nations†, after having done research in ten leading trading nations. The book was the first theory of competitiveness based on the causes of the productivity with which companies compete. Instead of traditional comparative advantages such as natural resources and pools of labor. This book should be considered obligatory reading for government economic strategists. It is also highly recommended for corporate strategists that are interested in the macro-economic environment of corporations.

Narrative and Descriptive Essay

The purpose between a narrative and descriptive essay differ from each other because of how you want to convey the story and how to accomplish the purpose. In How to Say Nothing in 500 Words, by Paul McHenry Roberts, the intended audience is for students and writers, and in Once More to the Lake, by E. B. White, it is for readers who had experience with sharing a moment with their loved ones, which both stories accomplish a specific audience. Other similarities between narrative and descriptive are the â€Å"description and narration are often used together because description helps make the story we are narrating clearer and more vivid† (Connell & Sole, 2013, p. 6.4), in which to accomplish their story, they both have a particular language it uses in order to do it. Roberts’s purpose is for the writer to exceed in their writing, though White’s purpose is to display past experiences may not be the same for others. What is similar to their story is that the reader can learn from the writers past errors. Roberts’s impact gives the reader a desire to want to write more effectively, although White’s story impacts the reader to enjoy an experience because it can lead to a disaster; both stories impact the reader to do something. The style of essay that is superior is narrative because a writer can â€Å"incorporate certain important elements in the narrative† (Connell & Sole, 2013, p. 6.3).When a writer uses descriptive, they tend to go too far using descriptive words to describe something that it becomes boring and it tends to make me skip that paragraph, and sometimes the entire page if it goes into too much detail. Reference Connell, C. M., & Sole, K. (2013). Essentials of College Writing (2nd ed.). San Diego, CA: Bridgepoint Education, Inc. Roberts, P. M. (n.d.). How to Say Nothing in 500 Words. Retrieved from https://docs.google.com/document/d/1Gw_UcMT4u-ZSW7ZBN_RAMspZFex6o83oIbnvtuV-CM8/edit?pli=1 White, E.B. Once More to the Lake. Retrieved from http://www.freewebs.com/lanzbom/EBWhiteLakeEssay.pdf

The Breakfast Club Essays

The Breakfast Club Essays The Breakfast Club Paper The Breakfast Club Paper This movie is undoubtedly the spitting image of high school today. It is amazing how the themes and actions back in the 80s are still well and alive in 2009. I guess teenagers just havent changed that much over the past 25 years. People still act the same way and treat people the same way. Kids still get teased and the preppies still rule the schools along with the jocks. Nerds are still getting picked on and the freaks are still eating lunch by themselves. It is quite funny how nothing has changed over the past 25 years. Yet, no one is too eager to try and change that. That is basically what this movie portrays, a group of teenagers that are forced into spending the day together in the school library. What could possibly go wrong? Back in the 80s, teenagers were very much into things like drinking, drugs, and sex. Nothing has changed since then. There are still the exact same cliques with the same type of people that partake in illegal activities. This movie, somehow, captures the whole aspect of a teenage life within 2 hours. It is amazing how the director could do that with a certain budget and time limit. Although it may seem easy to write a movie about teenagers, we are very complex at heart. The Breakfast Club is about a group of 5 teenagers, 1 jock, 1 prep. , 1 nerd, 1 freak, and 1 hooligan that are forced into spending the entire day in the school library because of certain things they decided to do. Youd think this would get out of hand within minutes. But, after a few fights and arguments, they just might surprise you near the end of the movie. Now, every teenagers worst nightmare is a horrible principal that wont get off your tail. Well this principal is everyones worst nightmare. Hes a bully at heart and a determined one at that. He has his mind set on getting everyone to like him. Even if that means knocking a few heads together. Its the weekend, and five students have weekend detention. Theres a jock, a princess, a freak, a nerd, and a hooligan. Not much in common, except for having to give up their day, sit in the school library, and write an essay for the principal. Being from such widely different backgrounds and having such completely different personalities, its obvious that some frictions and shenanigans will develop, especially when the principal leaves the room. The students pass the hours in a variety of ways: they dance, harass each other, tell stories, fight, smoke marijuana, and talk about many different things. They even open up to each other at certain points in the movie with some of their inner secrets (for example, Allison is a compulsive liar and Brian and Claire are ashamed of their virginity). They also discover that they all have wrecked relationships with their parents. However, besides these developing friendships, the students are afraid that once detention is over they will go back to living their normal lives and forget about the day the spent together.

Equivalence Point Definition

Equivalence Point Definition The equivalence point is a chemistry term youll encounter when you do a titration. However, it technically applies to any acid-base or neutralization reaction. Heres its definition and a look at methods used to identify it. Equivalence Point Definition The equivalence point is the point in a titration where the amount of titrant added is enough to completely neutralize the analyte solution. The moles of titrant (standard solution) equal the moles of the solution with unknown concentration. This is also known as the stoichiometric point because it is where the moles of acid are equal to the amount needed to neutralize the equivalent moles of base. Note this does not necessarily mean the acid to base ratio is 1:1. The ratio is determined by the balanced acid-base chemical equation. The equivalence point is not the same as the endpoint of a titration. The endpoint refers to the point at which an indicator changes color. More often than not, the color change occurs after the equivalence point has already been reached. Using the endpoint to calculate equivalence naturally introduces error. Key Takeaways: Equivalence Point The equivalence point or stoichiometric point is the point in a chemical reaction when there is exactly enough acid and base to neutralize the solution.In a titration, it is where the moles of titrant equal the moles of solution of unknown concentration. The acid to base ratio is not necessarily 1:1, but must be determined using the balanced chemical equation.Methods of determining the equivalence point include color change, pH change, formation of a precipitate, change in conductivity, or temperature change.In a titration, the equivalence point is not the same as the endpoint. Methods of Finding the Equivalence Point There are several different ways to identify the equivalence point of a titration: Color Change - Some reactions naturally change color at the equivalence point. This may be seen in redox titration, particularly involving transition metals, where the oxidation states have different colors. pH Indicator - A colored pH indicator may be used, which changes color according to pH. The indicator dye is added at the beginning of the titration. The color change at the endpoint is an approximation of the equivalence point. Precipitation - If an insoluble precipitate forms as a result of the reaction, it can be used to determine the equivalence point. For example, the silver cation and chloride anion react to form silver chloride, which is insoluble in water. However, it can be difficult to determine precipitation because the particle size, color, and sedimentation rate may make it difficult to see. Conductance - Ions affect the electrical conductivity of a solution, so when they react with each other, the conductivity changes. Conductance may be a difficult method to use, especially if other ions are present in the solution that can contribute to its conductivity. Conductance is used for some acid-base reactions. Isothermal Calorimetry - The equivalence point may be determined by measuring the amount of heat that is produced or absorbed using a device called an isothermal titration calorimeter. This method is often used in titrations involving biochemical reactions, such as enzyme binding. Spectroscopy: Spectroscopy can be used to find the equivalence point if the spectrum of the reactant, product, or titrant is known. This method is used to detect etching of semiconductors. Thermometric Titrimetry: In thermometric titrimetry, the equivalence point is determined by measuring the rate of temperature change produced by a chemical reaction. In this case, the inflection point indicates the equivalence point of an exothermic or endothermic reaction. Amperometry: In an ampometric titration, the equivalence point is seen as a change in the measured current. Amperometry is used when the excess titrant is able to be reduced. The method is useful, for example, when titrating a halide with Ag because it isnt affected by precipitate formation. Sources Khopkar, S.M. (1998). Basic Concepts of Analytical Chemistry (2nd ed.). New Age International. pp. 63–76. ISBN 81-224-1159-2.Patnaik, P. (2004). Deans Analytical Chemistry Handbook (2nd ed.). McGraw-Hill Prof Med/Tech. pp. 2.11–2.16. ISBN 0-07-141060-0.Skoog, D.A.; West, D.M.; Holler, F.J. (2000). Analytical Chemistry: An Introduction, 7th ed. Emily Barrosse. pp. 265–305. ISBN 0-03-020293-0.Spellman, F.R. (2009). Handbook of Water and Wastewater Treatment Plant Operations (2 ed.). CRC Press. p. 545. ISBN 1-4200-7530-6.Vogel, A.I.; J. Mendham (2000). Vogels Textbook of Quantitative Chemical Analysis (6th ed.). Prentice Hall. p. 423. ISBN 0-582-22628-7.

The Goal novel - Supply Chain Managment Essay Example | Topics and Well Written Essays - 250 words

The Goal novel - Supply Chain Managment - Essay Example The other way is to identify the hidden capacity within the plant be it in the machineries or the workers and utilize them. Alex identified that the goal of the plant and which he has to attain is to make money (Goldratt & Cox 46). In order to meet his goal, he will need anything that will bring him closer to attain it that is anything productive and identify all the bottlenecks preventing the attainment of the goal and do away with them. Managerial decision making is not an easy chore and it requires patience and a lot of team work. The manager also needs to seek advice from those with experience and try an all rounded approach for better results. Jonah was giving advice that was far too difficult and technical for Alex and it made him work even harder to figure it out, run the plant in the meanwhile and all these at the expense of his family. The more time he took to figure out Jonah’s advice, the more time his personal life