petrol vs diesel engine

The basic operation-- 4 stroke engines

Before going to the main topic let's have a look at the basic operation of a 4 stroke I.C engine. Both engines have the same basic 4 strokes: intake, compression, power, and exhaust. During the intake stroke fresh air is sucked in (or forced in) to the cylinder. The compression strokes compresses this gas and produces a hot gas. Fuel is burnt in this hot gas and the power stroke happens next. Please remember power stroke is the only stroke where the piston absorbs energy from the fuel. The last stroke is to eject the burn gas to the atmosphere

Difference betweenbetween petrol and diesel engines

There are differences between the two engines due to the difference between the way fuels burn. Petrol is a volatile fuel, is readily evaporates, so it gets mixed with the air efficiently. As a result, just a spark is sufficient to produce smooth combustion in a well pre-mixed petrol engine.petrol has a very low flash point. Flash point is the minimum temperature required for a liquid fuel to form a spontaneously combustible mixture.

On the other hand, diesel being a less volatile fuel does not properly mix with air.  diesel has such a high flash point value. However, if atomized diesel is sprayed into high-temperature air, spontaneous combustion will occur.

Why diesel engine are heavier?

You might have noticed that petrol engines are less noisy and vibrate less compared to diesel engines. This is because the combustion process in a pre-mixed mixture is smooth and propagates well But in a diesel engine, the combustion could begin anywhere in the combustion chamber, and it turns out to be an uncontrolled process.

 Combustion is smooth and well propagating in petrol engine, but in diesel it is highly unpredictable

For this reason, to reduce the excessive vibration and noise problem, diesel engines require a more rugged structural design than petrol engines. To normalize the heavy unbalanced power production of diesel engines a heavy fly wheel is often required. This is why petrol engines are always preferred for light-weight applications, such as in 2-wheeler or portable devices.

Petrol in diesel engine or vice-versa 

An interesting question many people wonder is: What if I put petrol into a diesel engine or vice versa?. From what we have learned so far, we will get a logical and practical answer for this intriguing question in this session

Diesel in petrol engine

Diesel in a petrol engine will not even cause firing. The reason is simple. Diesel is less volatile and will not mix with the air properly. In fact you will find it is impossible to make a good diesel-air mixture using carburetor or direct injection technology. This means if you apply spark to such a poor quality mixture, it will not initiate any combustion.

Petrol in diesel engine

On the other hand, if you put petrol in a diesel engine, you are spraying a highly volatile fuel into a chamber of highly compressed and hot air. This will lead to detonations rather than smooth combustion. Eventually, the engine components will get damaged. Moreover diesel generally acts a good lubricant for the fuel pump and the injection system. When you put petrol (which does not have any lubrication property) into a diesel car your are actually making the intricate components to wear down over the time. So that’s a big no for petrol in a diesel engine.

explanation on direct current motor (dc)

A DC motor is any of a class of electrical machines that converts direct current electrical power into mechanical power. The most common types rely on the forces produced by magnetic fields. Nearly all types of DC motors have some internal mechanism, either electromechanical or electronic, to periodically change the direction of current flow in part of the motor. Most types produce rotary motion; a linear motor directly produces force and motion in a straight line.

• DC motors were the first type widely used, since they could be powered from existing direct-current lighting power distribution systems. A DC motor's speed can be controlled over a wide range, using either a variable supply voltage or by changing the strength of current in its field windings. Small DC motors are used in tools, toys, and appliances. The universal motor can operate on direct current but is a lightweight motor used for portable power tools and appliances. Larger DC motors are used in propulsion of electric vehicles, elevator and hoists, or in drives for steel rolling mills. The advent of power electronics has made replacement of DC motors with AC motors possible in many applications.

how to improve your skill in calculus

Develop an effective and time-efficient homework/study strategy for, not only your calculus class, but other classes as well. This will help you become a more confident, successful, and well-rounded student. It will lead to a healthier balance between work time and leisure time.
Spend at least two to four hours on each homework assignment. This affords you extra time to work on challenging homework problems and helps you organize your thoughts, questions, and ideas. The more time you spend on homework, the more likely you are to articulate clear, concise questions to your classmates and teachers. The more time you spend on homework, the less time you will spend on frantic, last-minute preparation for exams.
Definitions, formulas, and theorems that are introduced in class or needed to complete homework assignments should be memorized immediately . Postponing this until it's needed for the exam will impede your work speed on homework assignments and interfere with clearer and deeper understanding of calculus.
Spend time working on calculus every day . Doing some calculus every day makes you more familiar with concepts, definitions, and theorems. This familiarity will make calculus get easier and easier one day at a time.
Find at least one or two other students from your calculus class with whom you can regularly do homework and prepare for exams. Your classmates are perhaps the least used and arguably your best resource. An efficient and effective study group will streamline homework and study time, reduce the need for attendance at office hours, and greatly improve your written and spoken communication. The best time to use your classmates as study/homework partners is after you have made an honest effort on your own to solve the problems using your own wits, knowledge, and experience. When you encounter an unsolvable problem, don't give up too soon on it. Being stumped is an opportunity for mathematical growth and insight, even if you never solve the problem on your own. If you seek help prematurely, you will never know if you could have solved a tough problem without outside assistance.
Begin preparing/outlining for exams at least five class days before the exam. Outlining the topics, definitions, theorems, equations, etc. that you need to know for the exam will help you focus on those areas where you are least prepared. Preparing early for the exam will build your self-confidence and reduce anxiety on the day of the exam. It's also an insurance policy against time lost to illness, unexpected family visits, and last-minute assignments in other classes. Generally speaking, pulling all-nighters and doing last-minute cramming for exams is a recipe for eventual academic disaster.
Prepare for exams by working on new problems . Good sources for these problems are unassigned problems from your textbook, review exercises and practice exams at the end of each chapter, old hour exams, or old final exams. Studying exclusively from those problems which you have already been assigned and worked on may not be effective exam preparation. Problems for each topic are generally in the same section of the book, so knowing how to do a problem because you know what section of the book it is in could give you a false sense of security. Working on new randomly mixed problems more closely simulates an exam situation, and requires that you both categorize the problem and then solve it.
Use all resources of assistance and information which are available to you. These include classnotes, homework solutions, office hours with your professor or teaching assistants, and problem sessions with your classmates. Do not rely exclusively on just one or two of these resources. Using all of them will help you develop a broader, more natural base of knowledge and understanding.
Expect your exams to be challenging.

100 motivational qoute that will inspire your success

100 Motivational Quotes That Will Inspire Your Success:

1. "If you want to achieve greatness stop asking for permission." --Anonymous

2. "Things work out best for those who make the best of how things work out." --John Wooden

3. "To live a creative life, we must lose our fear of being wrong." --Anonymous

4. "If you are not willing to risk the usual you will have to settle for the ordinary." --Jim Rohn

5. "Trust because you are willing to accept the risk, not because it's safe or certain." --Anonymous

6. "Take up one idea. Make that one idea your life--think of it, dream of it, live on that idea. Let the brain, muscles, nerves, every part of your body, be full of that idea, and just leave every other idea alone. This is the way to success." --Swami Vivekananda

7. "All our dreams can come true if we have the courage to pursue them." --Walt Disney

8. "Good things come to people who wait, but better things come to those who go out and get them." --Anonymous

9. "If you do what you always did, you will get what you always got." --Anonymous

10. "Success is walking from failure to failure with no loss of enthusiasm." --Winston Churchill

11. "Just when the caterpillar thought the world was ending, he turned into a butterfly." --Proverb

12. "Successful entrepreneurs are givers and not takers of positive energy." --Anonymous

13. "Whenever you see a successful person you only see the public glories, never the private sacrifices to reach them." --Vaibhav Shah

14. "Opportunities don't happen, you create them." --Chris Grosser

15. "Try not to become a person of success, but rather try to become a person of value." --Albert Einstein

16. "Great minds discuss ideas; average minds discuss events; small minds discuss people." --Eleanor Roosevelt

17. "I have not failed. I've just found 10,000 ways that won't work." --Thomas A. Edison

18. "If you don't value your time, neither will others. Stop giving away your time and talents--start charging for it." --Kim Garst

19. "A successful man is one who can lay a firm foundation with the bricks others have thrown at him." --David Brinkley

20. "No one can make you feel inferior without your consent." --Eleanor Roosevelt

21. "The whole secret of a successful life is to find out what is one's destiny to do, and then do it." --Henry Ford

22. "If you're going through hell keep going." --Winston Churchill

23. "The ones who are crazy enough to think they can change the world, are the ones who do." --Anonymous

24. "Don't raise your voice, improve your argument." --Anonymous

25. "What seems to us as bitter trials are often blessings in disguise." --Oscar Wilde

26. "The meaning of life is to find your gift. The purpose of life is to give it away." --Anonymous

27. "The distance between insanity and genius is measured only by success." --Bruce Feirstein

28. "When you stop chasing the wrong things, you give the right things a chance to catch you." --Lolly Daskal

29. "I believe that the only courage anybody ever needs is the courage to follow your own dreams." --Oprah Winfrey

30. "No masterpiece was ever created by a lazy artist." --Anonymous

31. "Happiness is a butterfly, which when pursued, is always beyond your grasp, but which, if you will sit down quietly, may alight upon you." --Nathaniel Hawthorne

32. "If you can't explain it simply, you don't understand it well enough." --Albert Einstein

33. "Blessed are those who can give without remembering and take without forgetting." --Anonymous

34. "Do one thing every day that scares you." --Anonymous

35. "What's the point of being alive if you don't at least try to do something remarkable." --Anonymous

36. "Life is not about finding yourself. Life is about creating yourself." --Lolly Daskal

37. "Nothing in the world is more common than unsuccessful people with talent." --Anonymous

38. "Knowledge is being aware of what you can do. Wisdom is knowing when not to do it." --Anonymous

39. "Your problem isn't the problem. Your reaction is

how make an AC

Air conditioning uses up 20 percent of all of the electricity used in the U.S. If you want to skip the expense of air conditioning or help the environment, then you can build your own air conditioner with either a box fan and a cooler or with a box fan and a radiator. Follow this guide to build your own air conditioner.

Ad
Method One of Two:
Build Your Own Air Conditioner with a Box Fan and a Cooler
Edit

1
Unscrew the front gridded panel of your box fan.

2
Twist 1/4" (6mm) diameter copper tubing in concentric circles starting at the center of the exterior side of your grid.
Attach the end of a length of copper tubing to the center of the grid using zip ties.

Twist the tubing into a tiny circle. Continue twisting the tubing around the original circle until you have a series of concentric circles. Connect the tube to the grid with zip ties.

You want plenty of tubing attached to your fan grid, but not so much that air can't pass through the spaces between the tubing.

3
Screw the front, with the tubing attached to the exterior, back onto the box fan.

4
Attach one end of a 3/8" (9.5 mm) clear pliable tube to your fountain pump and the other end to the top end of your copper tubing. The ideal tubing for this project is the type of tubing used in fish tanks.

5
Roll plumber's putty in your hands to form a strip. Wrap the putty around the connection between the hose and tubing and press the putty to seal the connection.

6
Connect the other piece of 3/8" (9.5 mm) plastic tubing to the bottom end of the copper tubing. Seal the connection with plumber's putty.

7
Wait an hour to allow your plumber's putty to dry.

8
Fill the cooler with ice water. Submerge the unconnected end of the second plastic tube beneath the water.

9
Place the fountain pump in the cooler.


10
Put a towel under your fan. The towel will catch the condensation that will form on the outside of the copper pipes.

11
Plug in the fountain pump and turn on the fan.

how to an inverter yourselve

How to Build an Inverter

To clearly understand how to build an inverter, let’s go through the following simple construction details:


As per the circuit schematic first complete the assembly of the oscillator section consisting of the smaller parts and the IC. It is best done by interconnecting the component leads itself and soldering the joints.
Next fit the power transistors into the appropriately drilled aluminum heat sinks. These are made by cutting an aluminum sheet into the given sizes and bending them at the edges so that it can be clamped.


Do not fit the transistors directly on to the heat sinks. Use mica isolation kit to avoid direct contact and short circuiting of the transistors with each other and the ground.
Clamp the heat sink assembly to the base of a well ventilated, sturdy, thick gauge metallic enclosure.
Also fix the power transformer beside the heat sinks using nuts and bolts.
Now connect the appropriate points of the assembled circuit board to the power transistors on the heat sinks.
Finally join the power transistor’s outputs to the secondary winding of the power transformer.
Finish the construction by fitting and interconnecting the external electrical “fittings" like fuses, sockets, switches, mains cord and the battery inputs.
An optional separate power supply circuit using a 12V/3Amp. transformer may be added inside to charge the battery whenever required
Circuit Description
To better understand how to build an inverter, it is important to learn how the circuit functions through nthe following steps:

Gates N1 and N2 of IC 4049 are configured as an oscillator. It performs the primary function of supplying square waves to the inverter section.
Gates N3... N6 are used as buffers so that the circuit is not load dependant.
Alternating voltage from the buffer stage is applied to the base of the current amplifier transistors T1 and T2. These transistors conduct in accordance with the applied alternating voltage and amplifies it to the base of the output transistors T3 and T4.
These output power transistors oscillate at a full swing, delivering the entire battery voltage into the each half of the secondary winding alternately.
This secondary voltage is induced in the primary winding of the transformer and is stepped-up into a powerful 230 volts (AC). This voltage is used to power the output load.
Testing Procedure
You can further understand how to build an inverter by concentrating on the following testing procedure given in a step-by-step manner below:



Begin the testing procedure by connecting a 100 watt bulb at the output socket of the inverter
Insert a 15 Amp./12V fuse inside the fuse holder
Finally connect a 12V automobile battery to the battery inputs of the inverter.
If all the connections are right, the 100 Watt bulb should immediately light up brightly.
Keep the inverter ON for an hour and let the battery discharge through the bulb
Then shift the given toggle switch to the charging mode, check the meter reading,
The meter should indicate the charging current of the battery.
The meter reading should gradually die down to zero after a span of time, confirming that the battery is fully charged and ready for the next cycle.

energy firm to create 500,000 jobs,50 mega walt of electricity

-The on-going efforts by the Buhari administration to turn around the national economy through stable power supply has received a boost as a foremost international solar energy company, Asteven Solar Nigeria, moves to create 500,000 direct jobs by accelerating access to affordable power solutions to old and existing small and medium enterprises across the country through specially designed channels. ...

a new e2o electric car made

Designed specifically for easy urban commuting, and featuring a host of connected technologies, the Mahindra e2o will be available in two trim levels. The entry-level e2o City is priced competitively. The higher-spec TechX version includes a touchscreen infotainment centre with reversing camera, telematics, revive remote emergency recharging, leather seats, alloy wheels and a rapid charging port.

In addition to its competitive purchase price, e2o owners that drive the UK average of 7,900 miles per year, and who charge at home at night on an Economy 7 tariff, will pay under £10 per month1 on fuel, while also eliminating the release of airborne pollutants within their city environment.

Speaking about the e2o's arrival on British roads, Anand Mahindra, Chairman, Mahindra Group said, "I am very proud to announce that the e2o is now available in the UK and this marks a true milestone for the Mahindra Group. Sustainability is at the heart of Mahindra's business practices and with the introduction of the e2o to the UK market, we are offering a product that perfectly encapsulates our corporate philosophy."

Pravin Shah, President & Chief Executive of Mahindra's Automotive operations believes that the e2o is the right car at the right time for the UK market and according to him, "There has never been a better time for people to make the change to electric, and with the e2o there has never been an easier or more affordable way to make this transition. The e2o is an innovative combination of advancements in automotive, electronics and information technology paired with minimal running costs and zero tailpipe emissions. This makes it the ideal urban runabout or second car for the two-and-a-half-million UK households that can charge the car at home in a driveway or garage."

At the launch of the e2o, Mayor of London, Boris Johnson MP said, "I want to congratulate Mahindra on the launch of their new electric car today. Supporting ultra-low emission vehicles has been a priority at City Hall as they can boost air quality, help tackle climate change and reduce fuel costs and I look forward to seeing e2os on London's streets."

At the core of the e2o is a collection of connected features that were developed to make the car both easier and more enjoyable to drive and maintain:

e2o Remote™ smartphone app - allows users to remotely control key functions of their e2o, including the ability to pre-heat/cool the car, start and stop charging, route plan and search for nearby charging stations.

Remote Charging Scheduler™ - a clever app that allows users to schedule charging of their e2o at a time when electricity costs are at their cheapest rate.

Revive™ - remote emergency charging feature to grant the driver up to 8 miles worth of range if the battery is depleted.

Telematics - on-board sensors send a data 'heartbeat' to Mahindra enabling remote health monitoring and customer alerts.

Blaupunkt touchscreen infotainment centre (TechX model only) - Satellite navigation with 'range remaining' maps featuring charge point locations. Bluetooth, Wi-Fi hotspot connection, USB, SD card, DAB radio and a built-in reversing camera.

The e2o's tall-boy design offers superior visibility for a compact city car and comfortably seats four adults. It is equipped with dual SRS airbags, Anti-Lock Braking System (ABS), Electronic Stability Control (ESC) and a Regenerative Braking System (RBS) that harnesses energy during braking to extend the car's range while travelling

what is a turbine?

A turbine (from the Latin turbo, a vortex, related to the Greek τύρβη, tyrbē, meaning "turbulence"),is a rotary mechanical device that extracts energy from a fluid flow and converts it into useful work. A turbine is a turbomachine with at least one moving part called a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades so that they move and impart rotational energy to the rotor. Early turbine examples are windmills and waterwheels.

Gas, steam, and water turbines have a casing around the blades that contains and controls the working fluid. Credit for invention of the steam turbine is given both to the British engineer Sir Charles Parsons (1854–1931), for invention of the reaction turbine and to Swedish engineer Gustaf de Laval (1845–1913), for invention of the impulse turbine. Modern steam turbines frequently employ both reaction and impulse in the same unit, typically varying the degree of reaction and impulse from the blade root to its periphery.

The word "turbine" was coined in 1822 by the French mining engineer Claude Burdin from the Latin turbo, or vortex, in a memo, "Des turbines hydrauliques ou machines rotatoires à grande vitesse", which he submitted to the Académie royale des sciences in Paris.[3] Benoit Fourneyron, a former student of Claude Burdin, built the first practical water turbine.

preparation of semiconductor

A large number of elements and compounds have semiconducting properties, including:[6]

Certain pure elements are found in Group 14 of the periodic table; the most commercially important of these elements are silicon and germanium. Silicon and germanium are used here effectively because they have 4 valence electrons in their outermost shell which gives them the ability to gain or lose electrons equally at the same time.
Binary compounds, particularly between elements in Groups 13 and 15, such as gallium arsenide, Groups 12 and 16, groups 14 and 16, and between different group 14 elements, e.g. silicon carbide.
Certain ternary compounds, oxides and alloys.
Organic semiconductors, made of organic compounds.
Most common semiconducting materials are crystalline solids, but amorphous and liquid semiconductors are also known. These include hydrogenated amorphous silicon and mixtures of arsenic, selenium and tellurium in a variety of proportions. These compounds share with better known semiconductors the properties of intermediate conductivity and a rapid variation of conductivity with temperature, as well as occasional negative resistance. Such disordered materials lack the rigid crystalline structure of conventional semiconductors such as silicon. They are generally used in thin film structures, which do not require material of higher electronic quality, being relatively insensitive to impurities and radiation damage.

Almost all of today’s technology involves the use of semiconductors, with the most important aspect being the integrated circuit (IC). Some examples of devices that contain integrated circuits includes laptops, scanners, cell-phones, etc. Semiconductors for ICs are mass-produced. To create an ideal semiconducting material, chemical purity is paramount. Any small imperfection can have a drastic effect on how the semiconducting material behaves due to the scale at which the materials are used.[4]

A high degree of crystalline perfection is also required, since faults in crystal structure (such as dislocations, twins, and stacking faults) interfere with the semiconducting properties of the material. Crystalline faults are a major cause of defective semiconductor devices. The larger the crystal, the more difficult it is to achieve the necessary perfection. Current mass production processes use crystal ingots between 100 and 300 mm (4 and 12 in) in diameter which are grown as cylinders and sliced into wafers.

There is a combination of processes that is used to prepare semiconducting materials for ICs. One process is called thermal oxidation, which forms silicon dioxide on the surface of the silicon. This is used as a gate insulator and field oxide. Other processes are called photomasks and photolithography. This process is what creates the patterns on the circuity in the integrated circuit. Ultraviolet light is used along with a photoresist layer to create a chemical change that generates the patterns for the circuit.[4]

Etching is the next process that is required. The part of the silicon that was not covered by the photoresist layer from the previous step can now be etched. The main process typically used today is called plasma etching. Plasma etching usually involves an etch gas pumped in a low-pressure chamber to create plasma. A common etch gas is chlorofluorocarbon, or more commonly known Freon. A high radio-frequency voltage between the cathode and anode is what creates the plasma in the chamber. The silicon wafer is located on the cathode, which causes it to be hit by the positively charged ions that are released from the plasma. The end result is silicon that is etched anisotropically.[2][4]

The last process is called diffusion. This is the process that gives the semiconducting material its desired semiconducting properties. It is also known as doping. The process introduces an impure atom to the system, which creates the p-n junction. In order to get the impure atom

history of semiconductor

The history of the understanding of semiconductors begins with experiments on the electrical properties of materials. The properties of negative temperature coefficient of resistance, rectification, and light-sensitivity were observed starting in the early 19th century.

In 1833, Michael Faraday reported that the resistance of specimens of silver sulfide decreases when they are heated. This is contrary to the behavior of metallic substances such as copper. In 1839, A. E. Becquerel reported observation of a voltage between a solid and a liquid electrolyte when struck by light, the photovoltaic effect. In 1873 Willoughby Smith observed that selenium resistors exhibit decreasing resistance when light falls on them. In 1874 Karl Ferdinand Braun observed conduction and rectification in metallic sulphides, although this effect had been discovered much earlier by M.A. Rosenschold writing for the Annalen der Physik und Chemie in 1835,[12] and Arthur Schuster found that a copper oxide layer on wires has rectification properties that ceases when the wires are cleaned. Adams and Day observed the photovoltaic effect in selenium in 1876.[13]

A unified explanation of these phenomena required a theory of solid-state physics which developed greatly in the first half of the 20th Century. In 1878 Edwin Herbert Hall demonstrated the deflection of flowing charge carriers by an applied magnetic field, the Hall effect. The discovery of the electron by J.J. Thomson in 1897 prompted theories of electron-based conduction in solids. Karl Baedeker, by observing a Hall effect with the reverse sign to that in metals, theorized that copper iodide had positive charge carriers. Johan Koenigsberger classified solid materials as metals, insulators and "variable conductors" in 1914, although his student Josef Weiss introduced term Halbleiter (semiconductor) in modern meaning in PhD thesis already in 1910.[14][15] Felix Bloch published a theory of the movement of electrons through atomic lattices in 1928. In 1930, B. Gudden stated that conductivity in semiconductors was due to minor concentrations of impurities. By 1931, the band theory of conduction had been established by Alan Herries Wilson and the concept of band gaps had been developed. Walter H. Schottky and Nevill Francis Mott developed models of the potential barrier and of the characteristics of a metal-semiconductor junction. By 1938, Boris Davydov had developed a theory of the copper-oxide rectifier, identifying the effect of the p–n junction and the importance of minority carriers and surface states.[16]

Agreement between theoretical predictions (based on developing quantum mechanics) and experimental results was sometimes poor. This was later explained by John Bardeen as due to the extreme "structure sensitive" behavior of semiconductors, whose properties change dramatically based on tiny amounts of impurities.[16] Commercially pure materials of the 1920s containing varying proportions of trace contaminants produced differing experimental results. This spurred the development of improved material refining techniques, culminating in modern semiconductor refineries producing materials with parts-per-trillion purity.

Devices using semiconductors were at first constructed based on empirical knowledge, before semiconductor theory provided a guide to construction of more capable and reliable devices.

Alexander Graham Bell used the light-sensitive property of selenium to transmit sound over a beam of light in 1880. A working solar cell, of low efficiency, was constructed by Charles Fritts in 1883 using a metal plate coated with selenium and a thin layer of gold; the device became commercially useful in photographic light meters in the 1930s.[16] Point-contact microwave detector rectifiers made of lead sulfide were used by Jagadish Chandra Bose in 1904; the cat's-whisker detector using natural galena or other materials became a common device in the development of radio. However, it was somewhat unpredic

properties of semiconductors

Variable conductivity
Semiconductors in their natural state are poor conductors because a current requires the flow of electrons, and semiconductors have their valence bands filled. There are several developed techniques that allow semiconducting materials to behave like conducting materials, such as doping or gating. These modifications have two outcomes: n-type and p-type. These refer to the excess or shortage of electrons, respectively. An unbalanced number of electrons would cause a current to flow through the material.[4]
Heterojunctions
Heterojunctions occur when two differently doped semiconducting materials are joined together. For example, a configuration could consist of p-doped and n-doped germanium. This results in an exchange of electrons and holes between the differently doped semiconducting materials. The n-doped germanium would have an excess of electrons, and the p-doped germanium would have an excess of holes. The transfer occurs until equilibrium is reached by a process called recombination, which causes the migrating electrons from the n-type to come in contact with the migrating holes from the p-type. A product of this process is charged ions, which result in an electric field.[2][4]
Excited Electrons
A difference in electric potential on a semiconducting material would cause it to leave thermal equilibrium and create a non-equilibrium situation. This introduces electrons and holes to the system, which interact via a process called ambipolar diffusion. Whenever thermal equilibrium is disturbed in a semiconducting material, the amount of holes and electrons changes. Such disruptions can occur as a result of a temperature difference or photons, which can enter the system and create electrons and holes. The process that creates and annihilates electrons and holes are called generation and recombination.[4]
Light emission
In certain semiconductors, excited electrons can relax by emitting light instead of producing heat.[5] These semiconductors are used in the construction of light emitting diodes and fluorescent quantum dots.
Thermal energy conversion
Semiconductors have large thermoelectric power factors making them useful in thermoelectric generators, as well as high thermoelectric figures of merit making them useful in thermoelectric coolers.

semiconductors

Semiconductors are crystalline or amorphous solids with distinct electrical characteristics.[1] They are of high resistance - higher than typical resistance materials, but still of much lower resistance than insulators. Their resistance decreases as their temperature increases, which is behavior opposite to that of a metal. Finally, their conducting properties may be altered in useful ways by the deliberate introduction of impurities ("doping") into the crystal structure, which lowers its resistance but also permits the creation of semiconductor junctions between differently-doped regions of the extrinsic semiconductor crystal. The behavior of charge carriers at these junctions is the basis of diodes, transistors and all modern electronics.

Semiconductor devices can display a range of useful properties such as passing current more easily in one direction than the other, showing variable resistance, and sensitivity to light or heat. Because the electrical properties of a semiconductor material can be modified by controlled addition of impurities, or by the application of electrical fields or light, devices made from semiconductors can be used for amplification, switching, and energy conversion.

The modern understanding of the properties of a semiconductor relies on quantum physics to explain the movement of electrons and holes (collectively known as "charge carriers") in a crystal lattice.[2] Doping greatly increases the number of charge carriers within the crystal. When a doped semiconductor contains mostly free holes it is called "p-type", and when it contains mostly free electrons it is known as "n-type". The semiconductor materials used in electronic devices are doped under precise conditions to control the concentration and regions of p- and n-type dopants. A single semiconductor crystal can have many p- and n-type regions; the p–n junctions between these regions are responsible for the useful electronic behavior.

Although some pure elements and many compounds display semiconductor properties, silicon, germanium, and compounds of gallium are the most widely used in electronic devices. Elements near the so-called "metalloid staircase", where the metalloids are located on the periodic table, are usually used as semiconductors.

Some of the properties of semiconductor materials were observed throughout the mid 19th and first decades of the 20th century. The first practical application of semiconductors in electronics was the 1904 development of the Cat's-whisker detector, a primitive semiconductor diode widely used in early radio receivers. Developments in quantum physics in turn allowed the development of the transistor in 1947[3] and the integrated circuit in 1958.

AIR CONDITIONER

Most homes in warm climates have air conditioning. For some, air conditioning may be a luxury, but for many, it is a necessity. Given the expense of the equipment and the power to run it, ASHRAE wants consumers to be informed about their air conditioning systems. These ten points should make a consumer more aware of the air conditioning system and better able to care for it and use it well. Should it become necessary to replace that system, seek out a qualified HVAC professional.
1. HOW AN AIR CONDITIONER WORKS

2. WHAT A “TON” OF COOLING IS

3. WHAT GOES WRONG

4. WHAT THOSE FILTERS DO

5. MAINTAIN THE SYSTEM

6. DUCTS MATTER - A LOT

7. HOW TO INCREASE ENERGY EFFICIENCY

8. LIGHTEN YOUR LOAD

9. VENTILATE

10. IT’S NOT THE HEAT, IT’S THE HUMIDITY
What is Air Conditioning?
The first functional definition of air-conditioning was created in 1908 and is credited to G. B. Wilson. It is the definition that Willis Carrier, the “father of air conditioning” subscribed to:
Maintain suitable humidity in all parts of a building
Free the air from excessive humidity during certain seasons
Supply a constant and adequate supply of ventilation
Efficiently remove from the air micro-organisms, dust, soot, and other foreign bodies
Efficiently cool room air during certain seasons
Heat or help heat the rooms in winter
An apparatus that is not cost-prohibitive in purchase or maintenance

HOW AN AIR CONDITIONER WORKS

The job of your home air conditioner is move heat from inside your home to the outside, thereby cooling you and your home. Air conditioners blow cool air into your home by pulling the heat out of that air. The air is cooled by blowing it over a set of cold pipes called an evaporator coil. This works just like the cooling that happens when water evaporates from your skin. The evaporator coil is filled with a special liquid called a refrigerant, which changes from a liquid to a gas as it absorbs heat from the air. The refrigerant is pumped outside the house to another coil where it gives up its heat and changes back into a liquid. This outside coil is called the condenser because the refrigerant is condensing from a gas back to a fluid just like moisture on a cold window. A pump, called a compressor, is used to move the refrigerant between the two coils and to change the pressure of the refrigerant so that all the refrigerant evaporates or condenses in the appropriate coils.
The energy to do all of this is used by the motor that runs the compressor. The entire system will normally give about three times the cooling energy that the compressor uses. This odd fact happens because the changing of refrigerant from a liquid to a gas and back again lets the system move much more energy than the compressor uses.

WHAT A 'TON' OF COOLING IS

Before refrigeration air conditioning was invented, cooling was done by saving big blocks of ice. When cooling machines started to get used, they rated their capacity by the equivalent amount of ice melted in a day, which is where the term “ton” came from sizing air conditioning.
A ton of cooling is now defined as delivering 12,000 BTU/hour of cooling. BTU is short for British Thermal Unit (and is a unit that the British do not use) The BTU is a unit of heating - or in this case, cooling - energy. It’s more important, however, to keep in perspective that a window air conditioner is usually less than one ton. A small home central air conditioner would be about two tons and a large one about five tons.

WHAT GOES WRONG

Unlike most furnaces, air conditioners are complex mechanical systems that depend on a wide variety of conditions to work correctly. They are sized to meet a certain “load” on the house. They are designed to have certain amount of refrigerant, known as the “charge”. They are designed to have a certain amount of air flow across the coils. When any of these things changes, the system will have problems.
If you produce more heat indoors either from having more people or appliance

electricity

Electricity is all around us–powering technology like our cell phones, computers, lights, soldering irons, and air conditioners. It’s tough to escape it in our modern world. Even when you try to escape electricity, it’s still at work throughout nature, from the lightning in a thunderstorm to the synapses inside our body. But what exactly is electricity? This is a very complicated question, and as you dig deeper and ask more questions, there really is not a definitive answer, only abstract representations of how electricity interacts with our surroundings.



Electricity is a natural phenomenon that occurs throughout nature and takes many different forms. In this tutorial we’ll focus on current electricity: the stuff that powers our electronic gadgets. Our goal is to understand how electricity flows from a power source through wires, lighting up LEDs, spinning motors, and powering our communication devices.

Electricity is briefly defined as the flow of electric charge, but there’s so much behind that simple statement. Where do the charges come from? How do we move them? Where do they move to? How does an electric charge cause mechanical motion or make things light up? So many questions! To begin to explain what electricity is we need to zoom way in, beyond the matter and molecules, to the atoms that make up everything we interact with in life.

This tutorial builds on some basic understanding of physics, force, energy, atoms, and fields in particular.

basic electronics

 

        Resistors

Resistors are truly iniquitous.They are almost as many types as thier applications. Resistors are employ in amplifiers as loads for active devices,in bias network,and as feedback  elements. in combination with capacitor  they establish time constant and act as filters,they are employed for setting operating current  and signals levels.They are employed in powerpower circuits to reduce voltage by dissipapower power,to measure current ,and to discharge capacitor after supply is removed.Resistor are employed in precision circuit to establish currents, to provide accurate voltage ratios and  to set precise gain values. In logic circuits they act as bus and line terminator and as "pull-up" and  "pull-down" resistors,in high-,voltage  circuit they are employ for measuring voltage and equalising leakage currents among diodes or capacitor connected in series. In radio frequency (RF) circuit they are even employed as coil forms for inductor