Self Reliance Written by Emerson Translation of Tamil Essay

Self Reliance Written by Emerson Translation of Tamil Essay.

A UPQC has the same structure as a UPFC. It can inject current in shunt and voltage in series simultaneously in a dual control mode. Therefore it can perform both the functions of load compensation and voltage control at the same time. The UPQC must also inject unbalanced and distorted voltages and currents and hence its operating characteristics are than that of a UPFC. Furthermore their operation philosophy is different. The UPQC is also an (PQ) enhancement device. UPFC and can operate under non-balanced conditions, whereas the UPFC is assumed to operate under balanced sinusoidal conditions.

Source: A. Ghosh, G. Ledwich – Power Qualtiy Enhancement using custom power devices (found at google: E-books) Quality of power supply has become an important issue with the increasing demand of Distributed Generation (DG) systems either connected to the grid through some power electronics grid-tie inverters or to work in isolated (microgrid) mode towards the development of a smart grid network. In this paper a technical review of Integration of Unified Power Quality Conditioner (UPQC) in Distributed Generation Network has been presented.

Though the primary task of UPQC is to minimize the grid voltage and load current disturbance along with the reactive and harmonic power compensation, additional functionalities like compensation of voltage interruption and active power transfer to the load and grid have also been identified. Connection methodologies with their pros and cons are also described. Recent improvements in capacity expansion techniques and future trends for the application of UPQC to cope up with the expanding DG capacity are also reviewed.

Self Reliance Written by Emerson Translation of Tamil Essay

Electric Generator Essay

Electric Generator Essay.

Early 20th century alternator made inBudapest, Hungary, in the power generating hall of a hydroelectric station In electricity generation, an electric generator is a device that converts mechanical energy to electrical energy. A generator forces electric charge (usually carried by electrons) to flow through an external electrical circuit. The source of mechanical energy may be a reciprocating or turbine steam engine, water falling through a turbine or waterwheel, aninternal combustion engine, a wind turbine, a hand crank, compressed air, or any other source of mechanical energy.

Generators supply almost all of the power for the electric power grids which provide most of the world’s electric power. The reverse conversion of electrical energy into mechanical energy is done by an electric motor, and motors and generators have many similarities. Many motors can be mechanically driven to generate electricity and frequently make acceptable generators.

History

Before the connection between magnetism and electricity was discovered, electrostatic generators were used. They operated on electrostaticprinciples.

Such generators generated very high voltage and low current. They operated by using moving electrically charged belts, plates, and disks that carried charge to a high potential electrode. The charge was generated using either of two mechanisms:

* Electrostatic induction

* The triboelectric effect, where the contact between two insulators leaves them charged. Because of their inefficiency and the difficulty of insulating machines that produced very high voltages, electrostatic generators had low power ratings, and were never used for generation of commercially significant quantities of electric power. The Wimshurst machine and Van de Graaff generator are examples of these machines that have survived. In 1827, Hungarian Anyos Jedlik started experimenting with the electromagnetic rotating devices which he called electromagnetic self-rotors, now called the Jedlik’s dynamo.

In the prototype of the single-pole electric starter (finished between 1852 and 1854) both the stationary and the revolving parts were electromagnetic. He formulated the concept of the dynamo at least 6 years beforeSiemens and Wheatstone but didn’t patent it as he thought he wasn’t the first to realize this. In essence the concept is that instead of permanent magnets, two electromagnets opposite to each other induce the magnetic field around the rotor. It was also the discovery of the principle of self-excitation.[1]

Faraday disk, the first electric generator. The horseshoe-shaped magnet (A) created a magnetic field through the disk (D). When the disk was turned, this induced an electric current radially outward from the center toward the rim. The current flowed out through the sliding spring contact m, through the external circuit, and back into the center of the disk through the axle. In the years of 1831–1832, Michael Faraday discovered the operating principle of electromagnetic generators. The principle, later called Faraday’s law, is that an electromotive force is generated in an electrical conductor which encircles a varying magnetic flux. He also built the first electromagnetic generator, called the Faraday disk, a type of homopolar generator, using a copper disc rotating between the poles of a horseshoe magnet. It produced a small DC voltage.

This design was inefficient, due to self-cancelling counterflows of current in regions that were not under the influence of the magnetic field. While current was induced directly underneath the magnet, the current would circulate backwards in regions that were outside the influence of the magnetic field. This counterflow limited the power output to the pickup wires, and induced waste heating of the copper disc. Later homopolar generators would solve this problem by using an array of magnets arranged around the disc perimeter to maintain a steady field effect in one current-flow direction.

Another disadvantage was that the output voltage was very low, due to the single current path through the magnetic flux. Experimenters found that using multiple turns of wire in a coil could produce higher, more useful voltages. Since the output voltage is proportional to the number of turns, generators could be easily designed to produce any desired voltage by varying the number of turns. Wire windings became a basic feature of all subsequent generator designs.

Dynamos are no longer used for power generation due to the size and complexity of the commutator needed for high power applications. This large belt-driven high-current dynamo produced 310 amperes at 7 volts, or 2,170 watts, when spinning at 1400 RPM.

Dynamo Electric Machine [End View, Partly Section] (U.S. Patent 284,110) The dynamo was the first electrical generator capable of delivering power for industry. The dynamo uses electromagnetic induction to convert mechanical rotation into direct currentthrough the use of a commutator. The first dynamo was built by Hippolyte Pixii in 1832. A dynamo machine consists of a stationary structure, which provides a constant magnetic field, and a set of rotating windings which turn within that field. On small machines the constant magnetic field may be provided by one or more permanent magnets; larger machines have the constant magnetic field provided by one or more electromagnets, which are usually called field coils. Through a series of accidental discoveries, the dynamo became the source of many later inventions, including the DC electric motor, the AC alternator, the AC synchronous motor, and the rotary converter.

Alternating current generating systems were known in simple forms from the discovery of the magnetic induction of electric current. The early machines were developed by pioneers such as Michael Faraday and Hippolyte Pixii. Faraday developed the “rotating rectangle”, whose operation was heteropolar – each active conductor passed successively through regions where the magnetic field was in opposite directions.[2] The first public demonstration of a more robust “alternator system” took place in 1886.[3] Large two-phase alternating current generators were built by a British electrician, J.E.H. Gordon, in 1882. Lord Kelvin andSebastian Ferranti also developed early alternators, producing frequencies between 100 and 300 Hz. In 1891, Nikola Tesla patented a practical “high-frequency” alternator (which operated around 15 kHz).[4]

After 1891, polyphase alternators were introduced to supply currents of multiple differing phases.[5] Later alternators were designed for varying alternating-current frequencies between sixteen and about one hundred hertz, for use with arc lighting, incandescent lighting and electric motors.[6] Large power generation dynamos are now rarely seen due to the now nearly universal use of alternating current for power distribution. Before the adoption of AC, very large direct-current dynamos were the only means of power generation and distribution. AC has come to dominate due to the ability of AC to be easily transformed to and from very high voltages to permit low losses over large distances. —

Electromagnetic generators
Dynamo
Main article: Dynamo

“Dynamo Electric Machine” (end view, partly section, U.S. Patent 284,110) A dynamo is an electrical generator that produces direct current with the use of a commutator. Dynamos were the first electrical generators capable of delivering power for industry, and the foundation upon which many other later electric-power conversion devices were based, including the electric motor, the alternating-current alternator, and the rotary converter. Today, the simpler alternator dominates large scale power generation, for efficiency, reliability and cost reasons. A dynamo has the disadvantages of a mechanical commutator. Also, converting alternating to direct current using power rectification devices (vacuum tube or more recently solid state) is effective and usually economic.

Alternator

Main article: Alternator

Without a commutator, a dynamo becomes an alternator, which is a synchronous singly fed generator. Alternators produce alternating current with a frequency that is based on the rotational speed of the rotor and the number of magnetic poles. Automotive alternators produce a varying frequency that changes with engine speed, which is then converted by a rectifier to DC. By comparison, alternators used to feed an electric power grid are generally operated at a speed very close to a specific frequency, for the benefit of AC devices that regulate their speed and performance based on grid frequency. Some devices such as incandescent lamps and ballast-operated fluorescent lamps do not require a constant frequency, but synchronous motors such as in electric wall clocks do require a constant grid frequency.

When attached to a larger electric grid with other alternators, an alternator will dynamically interact with the frequency already present on the grid, and operate at a speed that matches the grid frequency. If no driving power is applied, the alternator will continue to spin at a constant speed anyway, driven as a synchronous motor by the grid frequency. It is usually necessary for an alternator to be accelerated up to the correct speed and phase alignment before connecting to the grid, as any mismatch in frequency will cause the alternator to act as a synchronous motor, and suddenly leap to the correct phase alignment as it absorbs a large inrush current from the grid, which may damage the rotor and other equipment.

Typical alternators use a rotating field winding excited with direct current, and a stationary (stator) winding that produces alternating current. Since the rotor field only requires a tiny fraction of the power generated by the machine, the brushes for the field contact can be relatively small. In the case of a brushless exciter, no brushes are used at all and the rotor shaft carries rectifiers to excite the main field winding. [edit]Induction generator

Main article: induction generator

An induction generator or asynchronous generator is a type of AC electrical generator that uses the principles of induction motors to produce power. Induction generators operate by mechanically turning their rotor faster than the synchronous speed, giving negative slip. A regular AC asynchronous motor usually can be used as a generator, without any internal modifications. Induction generators are useful in applications such as minihydro power plants, wind turbines, or in reducing high-pressure gas streams to lower pressure, because they can recover energy with relatively simple controls. To operate an induction generator must be excited with a leading voltage; this is usually done by connection to an electrical grid, or sometimes they are self excited by using phase correcting capacitors. [edit]MHD generator

Main article: MHD generator

A magnetohydrodynamic generator directly extracts electric power from moving hot gases through a magnetic field, without the use of rotating electromagnetic machinery. MHD generators were originally developed because the output of a plasma MHD generator is a flame, well able to heat the boilers of a steam power plant. The first practical design was the AVCO Mk. 25, developed in 1965. The U.S. government funded substantial development, culminating in a 25 MW demonstration plant in 1987. In the Soviet Union from 1972 until the late 1980s, the MHD plant U 25 was in regular commercial operation on the Moscow power system with a rating of 25 MW, the largest MHD plant rating in the world at that time.[7] MHD generators operated as a topping cycle are currently (2007) less efficient than combined cycle gas turbines. [edit]Other rotating electromagnetic generators

Other types of generators, such as the asynchronous or induction singly fed generator, the doubly fed generator, or the brushless wound-rotor doubly fed generator, do not incorporate permanent magnets or field windings that establish a constant magnetic field, and as a result, are seeing success in variable speed constant frequency applications, such as wind turbines or otherrenewable energy technologies. The full output performance of any generator can be optimized with electronic control but only the doubly fed generators or the brushless wound-rotor doubly fed generator incorporate electronic control with power ratings that are substantially less than the power output of the generator under control, a feature which, by itself, offers cost, reliability and efficiency benefits.

Homopolar generator

Main article: Homopolar generator

Faraday disk, the first homopolar generator

A homopolar generator is a DC electrical generator comprising an electrically conductive disc or cylinder rotating in a plane perpendicular to a uniform static magnetic field. A potential difference is created between the center of the disc and the rim (or ends of the cylinder), the electrical polaritydepending on the direction of rotation and the orientation of the field. It is also known as a unipolar generator, acyclic generator, disk dynamo, orFaraday disc. The voltage is typically low, on the order of a few volts in the case of small demonstration models, but large research generators can produce hundreds of volts, and some systems have multiple generators in series to produce an even larger voltage.[8] They are unusual in that they can source tremendous electric current, some more than a million amperes, because the homopolar generator can be made to have very low internal resistance.

Excitation

A small early 1900s 75 KVA direct-driven power station AC alternator, with a separate belt-driven exciter generator. Main article: Excitation (magnetic) An electric generator or electric motor that uses field coils rather than permanent magnets requires a current to be present in the field coils for the device to be able to work. If the field coils are not powered, the rotor in a generator can spin without producing any usable electrical energy, while the rotor of a motor may not spin at all. Smaller generators are sometimes self-excited, which means the field coils are powered by the current produced by the generator itself. The field coils are connected in series or parallel with the armature winding.

When the generator first starts to turn, the small amount of remanent magnetism present in the iron core provides a magnetic field to get it started, generating a small current in the armature. This flows through the field coils, creating a larger magnetic field which generates a larger armature current. This “bootstrap” process continues until the magnetic field in the core levels off due to saturation and the generator reaches a steady state power output. Very large power station generators often utilize a separate smaller generator to excite the field coils of the larger. In the event of a severe widespread power outage where islanding of power stations has occurred, the stations may need to perform a black start to excite the fields of their largest generators, in order to restore customer power service.

Electrostatic generator
Main article: electrostatic generator

A Van de Graaff generator, for class room demonstrations

An electrostatic generator, or electrostatic machine, is a mechanical device that produces static electricity, or electricity at high voltage and lowcontinuous current. The knowledge of static electricity dates back to the earliest civilizations, but for millennia it remained merely an interesting and mystifying phenomenon, without a theory to explain its behavior and often confused with magnetism. By the end of the 17th Century, researchers had developed practical means of generating electricity by friction, but the development of electrostatic machines did not begin in earnest until the 18th century, when they became fundamental instruments in the studies about the new science of electricity.

Electrostatic generators operate by using manual (or other) power to transform mechanical work into electric energy. Electrostatic generators develop electrostatic charges of opposite signs rendered to two conductors, using only electric forces, and work by using moving plates, drums, or belts to carry electric charge to a high potentialelectrode. The charge is generated by one of two methods: either the triboelectric effect (friction) or electrostatic induction. [edit]Wimshurst machine

Main article: Wimshurst machine

Wimshurst machine with two Leyden jars.Suppose that the conditions are as in the figure, with the segment A1 positive and the segment B1 negative. Now, as A1 moves to the left and B1 to the right, their potentials will rise on account of the work done in separating them against attraction. When A1 and neighboring sectors comes opposite the segment B2 of the B plate, which is now in contact with the brush Y, they will cause a displacement of electricity along the conductor between Y and Y1 bringing a negative charge, larger than the positive charge in A1 alone, on Y and sending a positive charge to the segment touching Y1.

As A1 moves on, it passes near the brush Z and is partially discharged into the external circuit. It then passes on until, on touching the brush X, has a new charge, this time negative, driven into it by induction from B2 and neighboring sectors. As the machine turns, the process causes exponential increases in the voltages on all positions, until sparking occurs limiting the increase.| The Wimshurst influence machine is an electrostatic generator, a machine for generating high voltages developed between 1880 and 1883 by Britishinventor James Wimshurst (1832–1903). It has a distinctive appearance with two large contra-rotating discs mounted in a vertical plane, two crossed bars with metallic brushes, and a spark gap formed by two metal spheres.

Van de Graaff generator

Main article: Van de Graaff generator

A Van de Graaff generator is an electrostatic generator which uses a moving belt to accumulate very high voltages on a hollow metal globe on the top of the stand. It was invented by American physicist Robert J. Van de Graaff in 1929. The potential difference achieved in modern Van de Graaff generators can reach 5 megavolts. The Van de Graaff generator can be thought of as a constant-current source connected in parallel with a capacitorand a very large electrical resistance, so it can produce a visible electrical discharge to a nearby grounding surface which can potentially cause a “spark” depending on the voltage.

Electric Generator Essay

Circuits Experiment Essay

Circuits Experiment Essay.

1. Describe the type of meter movement used in analog meters.

The current in the circuit is used in basic meters to measure the voltage drop or current in the circuit. The current passes through the coils of wires, which is then magnetized. Inside the apparatus, there is also a permanent magnet which opposes the magnetic field of the magnetized coil of wire that is connected to the pointer therefore, as we see in meters, the pointer moves. There is also a spring connected to the pointer to counteract the torque produced by the pointer, so the pointer will move in proportionality with the current density.

As the current increases, the pointer will travel farther. When the current is interrupted, the field will also be gone, and the pointer will go back to zero by the spring.

2. What device is used to extend the range of a DC ammeter and how is it connected to the basic meter?

An additional resistance, which is called shunt resistor, is placed in parallel with the galvanometer of an ammeter to extend the range of the DC ammeter.

The added resistance must be less than the resistance of the galvanometer to attract more current and the ammeter itself will receive less current, but will not affect the total current of the circuit, therefore extending the full scale range of the ammeter.

3. What device is used to extend the range of a DC voltmeter and how is it connected to the basic meter?

An additional resistor, which is called multiplier resistor, is placed in series with the galvanometer of a voltmeter to extend the range of the DC voltmeter. The added resistance will cause the path of the voltmeter to draw less current without changing the voltage of the voltage source, therefore extending the full scale range of the voltmeter.

4. Why is it necessary that an ammeter be a low resistance instrument? Why must a voltmeter be a high resistance instrument?

The ammeter must be a low resistance instrument, because if the ammeter will have a decent to high resistance it will affect the total resistance of the circuits resulting to a change in current flowing throughout the circuit, which will lead to an incorrect reading of the ammeter. The ideal voltmeter has infinite resistance, because it is place parallel to the circuit, but since it is impossible to get a infinite resistance, it should be as high as possible to receive less current. Another reason is that when the current arrives in a junction of a parallel path, most current will tend to go to the least resistive path. When one of the paths is the voltmeter, no current must pass through the voltmeter, so that the voltmeter won’t change anything with the circuit.

5. What type of basic meter is configured as a wattmeter?

There are two coils in a wattmeter. One coil is placed in series with the circuit and the other one is placed in parallel with the circuit. The deflection of the pointer will be proportional to both coil resulting to the magnitude of power, which follows the P=VI.

6. Two 150 V voltmeters are being compared; meter A has 5 k|/V while meter B has a total meter resistance of 750 k|. Which is the more sensitive meter? Why?

Both 150V voltmeters have the same sensitivity of 5kohms/V. The sensitivity of a voltmeter is taken by dividing the resistance of the voltmeter by the full scale voltage reading of the voltmeter. Meter B has a resistance of 750Kohms, dividing it by 150V will have a quotient of 5kohms/V, which is also the same with the meter A.

Circuits Experiment Essay

Science Report on Electromagnetism Essay

Science Report on Electromagnetism Essay.

This report will be done on the theory of Electromagnetism. Electromagnetism is the force that combines electricity and magnetism. Electromagnetism is found in everyday things that shape our lives. It is the cleanest force used to make energy today, and it is used in almost every home appliance that is in a standard middle classed home. The E-M force is the most commonly under looked force that helps us live. Without Electromagnetism, we would be falling through floors, literally! E-M force can be found even in military weapons, and even the radio uses electromagnetism.

Electromagnetism can save lives when used in critical medical equipment. This is one truly amazing force that we can no longer overlook if we wish to live a normal, healthy, and fun life. Electromagnetism, the most common, yet overlooked force that shapes out lives. (This is the first of my several subtopics dealing with the E-M force. This particular subtopic deals with electromagnetism’s general uses. Electromagnetism is commonly used in microwaves, remote control cars, and it creates energy cleanly and fast.

One of the most important uses for electromagnetism is in electronic motors. The main components are a core rod and many copper wires coiling around the iron rod. The coils rotate around the iron rod because of the magnetic force caused by a certain magnetic field on an electric current. While doing so, this turns electrical energy into mechanical energy. When this happens, normally a gear is attached to the end of the rod. That Gear is connected to another gear and that can be linked to anything you want to turn. However, when you reverse this process of making electrical energy into mechanical energy, it creates energy. This can be done with windmills, in dams, and in underwater tunnels that are specifically made for making energy.

The way that works is that instead of the copper wires turning and making the iron rod turn, the copper coils. These windmills are actually called wind turbines. These wind turbines can vary in size greatly. Some can be fit on your roof, some need to be installed on big hills were the wind blows. Now that we are done talking about wind turbines, electromagnetism is used in remote control cars because of the electric motors. Some remote control cars use gasoline as their source but we will not get into that. Microwaves use electromagnetism the same way as remote controlled cars do. When their plate rotates, there is an engine under the plate. It is also sometimes used to create radio waves which are the main source of heat in the microwave.

This paragraph will be talking about electromagnetism’s history. In April 21, 1820, while preparing for a lecture, Hans Christian Orsted designed an experiment which provided evidence that surprised him. As he was preparing his materials, he noticed that a compass needle deflected from magnetic poles north when the electric current from the battery he was using was switched on and off. This deflection convinced him that magnetic fields radiate from all sides of a wire carrying an electric current, just as light and heat do, and that it confirmed a direct relationship between electricity and magnetism. When that occurred, Hans did not continue further experimentation, nor did he try to do the math of what he had seen. However, three months later, Hans decided that he should do more study and so he did thereafter publishing his studies. His studies then continued on and still do throughout these modern years. As our understanding for electromagnetism continues to grow, it becomes increasingly helpful to us.

This subtopic will be about how an electromagnet works and how it can be created. Electromagnets at the most basic form can be made by copper coils, iron rods, and a battery. Depending on what kind of job it will do, the power source will differentiate. When the electromagnet is built, it almost has the same properties as a natural magnet. The Electromagnet produces a magnetic field and it has a positive and negative side. The benefits of an electromagnet are that you can control its strength by increasing the power to the copper wire. “Electromagnets work when electricity is forced through the copper coil that is coiled around an Iron rod.

You can connect the copper wires to a battery or any other kind of power source, then use the electromagnet as you wish. Now the way an electromagnet works is that you send an electrical current through the coil. When that happens the battery produces electrons. Electrons collect at the negative end of the battery, and, if you let them, they will gladly flow to the positive end. The way you “let them” flow is with a wire. If you attach a wire directly between the positive and negative terminals of a D-cell battery, three things will happen:1.Electrons will flow from the negative side of the battery to the positive side as fast as they can.

2.The battery will drain very quickly. For that reason, it is generally not a good idea to connect the two terminals of a battery to one another directly. Normally, you connect some kind of load in the middle of the wire so the electrons can do useful work. The load might be a motor, a light bulb, a radio or whatever.

3.A small magnetic field is generated in the wire. It is this small magnetic field that is the basis of an electromagnet.”This is spoken of on http://science.howstuffworks.com/electromagnet2.htm.

This is subtopic will be about how the electromagnetism force shapes the human life and how it makes our bodies work the way it does. First, as your have read earlier in my introduction, that without electromagnetism, we’d be falling through walls, floors, and anything else. The reason for this is because atoms produce electrons which have electromagnetic properties. These properties force the atoms to stick together so that our body has a solid structure and that our body doesn’t just fall apart into millions of atoms. And since everything in our bodies is made of atoms, if there was no electromagnetism, there would be no life or and no world. The earth and all the other planets revolve around the sun because of its giant magnetic field.

The end of this report is that the electromagnets are essential to modern day life and will continue to make our minds think more and more about this force. Electromagnetism will be there to help us all the way through life and as we get older, we will find new uses for electromagnetism. The electromagnetism force is also essential to our bodies and it will keep us intact. This is the most under looked and underestimated force that shapes our lives, keeps us alive, and makes our life easier. Thank you for reading this report.

Bibliography

-http://science.howstuffworks.com/electromagnet2.htm.

Science Report on Electromagnetism Essay

Resistors in series and parallel Essay

Resistors in series and parallel Essay.

Resistors are used in various real life applications to perform tasks that involve: limiting the current that goes through a section of a circuit, introducing a voltage drop in a circuit, generating heat and the protection of components of a circuit. It is important to calculate the resistance of resistors so that the electrical circuits produced using them will perform in the manner that their manufacturer wanted them to. If the wrong resistance/resistor is used then delicate components that need only a relatively small amount of current may be destroyed.

All resistors have a level of tolerance. This is to allow for imperfections in the manufactured object. It was determined through experimentation that all of the resistors that were used in this experiment were within their tolerance range with the exception of R4 (See Table 1). This resistor had a nominal value of 1600 ohms and a tolerance of +/-5%. This means that this resistor should have had a value within the range of 1520-1680 ohms, however the actual resistance was found to be 1798 ohms.

It is possible that this may have been due to a manufacturing fault or a labelling error.

The total predicted resistance was determined by using the series and parallel resistor laws and the resistance values of the various components of the circuit. The tolerance range for the circuit was predicted to be between 1847.3-2319.2 ohms. Through experimentation the actual total resistance for the circuit was 2216.62 ohms, this value was within the predicted range.

The actual resistance value of component 1 was 263.26 ohms; this was within the predicted range (271.36-245.51 ohms).

The actual resistance value of component 2 was 1764.26 ohms; this was within the predicted range (1664.24-1846.36 ohms).

The actual resistance value of component 3 was 2216.62 ohms; this was within the predicted range (2319.20 and 1847.3 ohms).

The actual resistance of the resistors was found by using a multimeter. Some systematic error may have occurred in this experiment if the multimeter was not calibrated correctly during testing.

Temperature fluctuations may have caused inconsistencies in this experiment. The reason why resistance occurs is that a metal consists of lattice of atoms that each has a shell of electrons. The metal is a conductor because the electrons are free to dissociate from their parent atoms and travel through the lattice. When a voltage is applied the electrons drift from one side of the metal to the other. In real material imperfections scatter the electrons resulting in resistance. Temperature is able to affect resistance because temperature causes the atoms to vibrate more strongly creating even more collisions and further increasing the resistance.

Conclusion:

The aim of the experiment was to compare the predicted and actual resistance in the circuit of resistor combinations in series and parallel. The results of this experiment found that the series and parallel resistor laws were reasonably good indicators of the “real world” values of resistance for circuits that contained resistors in series and parallel. One example of this was that the total resistance of the circuit made was found to be 2216.62 ohms which was within the predicted range (this predicted range was calculated by using the upper and lower tolerance values for the resistors used in the circuit. From the data obtained it can therefore be seen that all three resistor laws stated in the Background section of this report are quite useful in calculating theoretical values for the resistance of circuits in series and parallel that are close to the “real world” values.

Bibliography:

“resistor.” Wikipedia. Wikipedia, 2005.

Available: http://www.answers.com/topic/resistor-1 24 Jul. 2005.

“resistor.” WordNet 1.7.1. Princeton University, 2001.

Available: http://www.answers.com/topic/resistor-1 24 Jul. 2005.

“resistor.” Electronics. Twysted Pair, 2001.

Available: http://www.answers.com/topic/resistor-1. 24 Jul. 2005.

Storen, A and Martine, R. (2000) Nelson Physics VCE Units 3 and 4. Nelson Publishing: Sydney. (pp 221-226)

Resistors in series and parallel Essay

One application of magnetic fields in household appliances Essay

One application of magnetic fields in household appliances Essay.

One thing that uses magnetic fields is the electric motor, which is used in many household appliances, such as electric fans, microwave ovens, and other small appliances. In this instance the electric motor has an electric current, giving it also this magnetic field.

An electric motor converts electricity into mechanical motion.

Most electric motors work by electromagnetism, but motors based on electrostatic forces also exist. The overarching concept is that a force is generated when a current-carrying element is subjected to a magnetic field.

In a cylindrical motor, the rotor rotates because a torque is developed when this force is applied at a given distance from the axis of the rotor.

Most electromagnetic motors are rotary, but linear types also exist. In a rotary motor, the rotating part (usually on the inside) is called the rotor, and the stationary part is called the stator. The motor contains electromagnets that are wound on a frame. Though this frame is often called the armature.

The electromagnetic field works as shown in the diagrams below.

DC motors.

A simple DC electric motor. When the coil is powered, a magnetic field is generated around the armature. The left side of the armature is pushed away from the left magnet and drawn toward the right, causing rotation.

The armature continues to rotate.

When the armature becomes horizontally aligned, the commutator reverses the direction of current through the coil, reversing the magnetic field. The process then repeats.

Single-phase AC induction motors.

Electric motors have no electrical connection between the rotor and the outside world. They operate due to a moving magnetic field induces a current to flow in the rotor. This current flow in the rotor creates the second magnetic field required to produce a torque. The motor was introduced in 1888 and it initiated what is known as the second industrial revolution, making possible the efficient generation and long distance distribution of electrical energy using the alternating current transmission system.

A common single-phase motor is the shaded pole motor, which is used in devices requiring lower torque, such as electric fans, microwave ovens, and other small household appliances. In this motor, small single-turn copper “shading coils” create the moving magnetic field.

Another common single-phase AC motor is the split-phase induction motor, commonly used in major appliances such as washing machines and clothes dryers. Compared to the shaded pole motor, these motors can generally provide much greater starting torque by using a special startup winding along with a centrifugal switch and a starting capacitor.

Three-phase AC motors.

For higher-power applications where a polyphase electrical supply is available, the three phase AC induction motor is used. The phase differences between the three phases of the polyphase electrical supply create a rotating electromagnetic field in the motor. There are two types of rotors in use.

Through electromagnetic induction, the rotating magnetic field creates a current in these conductors, which in turn sets up a counterbalancing magnetic field that causes the rotor to turn in the direction that the field is rotating.

This type of motor is becoming more common in appliances such as locomotives, where it is known as the asynchronous traction motor. If the rotor coils are fed a separate field current to create a continuous magnetic field, the result is a called a synchronous motor because the motor rotates in synchronism with the rotating magnetic field produced by the three phase electrical supply.

Bibliography.

An electric motor converts electrical energy into mechanical motion. The reverse task, that of converting mechanical motion into electrical energy, is accomplished by a generator or dynamo. In many cases the two devices differ only in their application and minor construction details. Electrical energy or Electromagnetic energy is a form of energy present in any electric field or magnetic field, or in any volume containing electromagnetic radiation. …

Most electric motors work by electromagnetism, but motors based on other electromechanical phenomena, such as electrostatic forces and the piezoelectric effect, also exist. The fundamental principle upon which electromagnetic motors are based is that there is a mechanical force on any wire when it is conducting electricity while contained within a magnetic field. The force is described by the Lorentz force law and is perpendicular to both the wire and the magnetic field. In a rotary motor, there is a rotating element, the rotor. The rotor rotates because the wires and magnetic field are arranged so that a torque is developed about the rotor’s axis. In physics, magnetism is a phenomenon by which materials exert an attractive or repulsive force on other materials. … An electrostatic motor or capacitor motor is a type of electric motor based on the attraction and repulsion of electric charge. … Piezoelectricity is the ability of certain crystals to produce a voltage when subjected to mechanical stress. … In physics, the Lorentz force is the force exerted on a charged particle in an electromagnetic field. …

Most magnetic motors are rotary, but linear types also exist. In a rotary motor, the rotating part (usually on the inside) is called the rotor, and the stationary part is called the stator. The motor contains electromagnets that are wound on a frame. Though this frame is often called the armature, that term is often erroneously applied. Correctly, the armature is that part of the motor across which the input voltage is supplied or that part of the generator across which the output voltage is generated. Depending upon the design of the machine, either the rotor or the stator can serve as the armature. r0t0r > * http://www. … The stator is the fixed part of a rotating machine. … In the physical sciences, potential difference is the difference in potential between two points in a conservative vector field. …

DC motors.

One of the first electromagnetic rotary motors, if not the first, was invented by Michael Faraday in 1821, and consisted of a free-hanging wire dipping into a pool of mercury. A permanent magnet was placed in the middle of the pool. When a current was passed through the wire, the wire rotated around the magnet, showing that the current gave rise to a circular magnetic field around the wire. This motor is often demonstrated in school physics classes, but brine is sometimes used in place of the toxic mercury. This is the simplest form of a class of electric motors called homopolar motors. Michael Faraday Michael Faraday (September 22, 1791 – August 25, 1867) was a British scientist (a physicist and chemist) who contributed significantly to the fields of electromagnetism and electrochemistry.

The classic DC motor has a rotating armature in the form of an electromagnet with two poles. A rotary switch called a commutator reverses the direction of the electric current twice every cycle, to flow through the armature so that the poles of the electromagnet push and pull against the permanent magnets on the outside of the motor. As the poles of the armature electromagnet pass the poles of the permanent magnets, the commutator reverses the polarity of the armature electromagnet. During that instant of switching polarity, inertia keeps the classical motor going in the proper direction. (See the diagrams below.) Direct current (DC or continuous current) is the continuous flow of electricity through a conductor such as a wire from high to low potential. … A commutator is an electrical switch that periodically reverses the current in an electric motor or electrical generator. … Inertia is the tendency of any state of affairs to persist in the absence of external influences. …

However, there are a number of limitations in the classic design, many due to the need for brushes to rub against the commutator. The rubbing creates friction, and the higher the speed, the harder the brushes have to press to maintain good contact. Not only does this friction make the motor noisy, but it also creates an upper limit on the speed and causes the brushes eventually to wear out and to require replacement. The imperfect electric contact also causes electrical noise in the attached circuit.

These problems vanish when you turn the motor inside out, putting the permanent magnets on the inside and the coils on the outside thus designing out the need for brushes in a brushless design. However such designs need electronic cuircuits to control the switching of the electromagnets (the function that is performed in conventional motors by the commutator). This article is about the resistive force. … … A brushless DC motor is an electric motor that operates like a DC motor, but with the roles of the rotor and stator reversed. …

AC motors.

Induction motors operate because a moving magnetic field induces a current to flow in the rotor. This current in the rotor creates the second magnetic field required (along with the field from the stator windings) to produce a torque. Induction motors are simple and therefore relatively cheap to construct. They do not rely on brushes like the DC motor, and usually have a longer life. They are by far the most common type of motor for applications above 1 kW. Typically the rotor has no electrical connection to the outside world, except in the case of wound-rotor induction motors. Electromagnetic induction is the production of an electrical potential difference (or voltage) across a conductor situated in a changing magnetic flux. …

All induction motors are characterized by the fact that when no load is applied to the motor, the rotor rotates at a slightly slower rate than the mains frequency (or an integer submultiple of the mains frequency). This is because the rotor must “slip” backwards against the moving magnetic field in order to induce any current in the rotor. The slip increases (and the motor speed decreases) as the load on the motor increases.

The rotating magnetic field principle was conceived by Nikola Tesla in 1882 and he employed it to invent a two-phase induction motor in 1883. Michael von Dolivo-Dobrowlsky invented the first modern three-phase “cage-rotor” in 1890. Introduction of the motor from 1888 onwards initiated what is known as the second industrial revolution, making possible the efficient generation and long distance distribution of electrical energy using the alternating current transmission system, also of Tesla’s invention (1888)[1] (http://www.tfcbooks.com/tesla/system.htm). A notable recent invention by Anadish K. Pal (U.S Patent 6717300) is to use an induction motor to sense its own rotation in the absence of the driving electric power. This invention has applications in alarm systems and early failure prediction of the induction motors. Nikola Tesla was an inventor, and electrical engineer. …

AC motors generally come in two types: single phase and three phase. An alternating current (AC) is an electrical current where the magnitude and direction of the current varies cyclically, as opposed to direct current, where the direction of the current stays constant. … The generation of AC electric power is commonly three phase, in which the waveforms of three supply conductors are offset from one another by 120°. These three conductors are commonly housed in a single conduit (e. … Three phase voltages Three phase systems have 3 waveforms (usually carrying power) that are 2/3 960; radians (120 degrees,1/3 of a cycle) offset in time. …

Single-phase AC induction motors.

A polyphase induction motor will continue to rotate even if one phase is disconnected, at reduced torque. However, a polyphase motor at standstill will not generate any net starting torque if connected only to a single-phase supply. The key to the design of single-phase motors, then, is to provide a rotating magnetic field to produce starting torque.

A common single-phase motor is the shaded pole motor, which is used in devices requiring lower torque, such as electric fans, microwave ovens, and other small household appliances. In this motor, small single-turn copper “shading coils” create the moving magnetic field. Part of each pole is encircled by a copper coil or strap; the induced current in the strap opposes the change of flux through the coil (Lenz’s Law), so that the maximum field intensity moves across the pole face on each cycle. small shaded-pole motor shading-coils A Shaded pole motor is a type of AC single phase induction motor. … The concept of torque in physics, also called moment or couple, originated with the work of Archimedes on levers. … Household Electric Fan A fan has two purposes. … Microwave oven A microwave oven is a kitchen appliance employing microwave radiation primarily to cook or heat food. …

Another common single-phase AC motor is the split-phase induction motor, commonly used in major appliances such as washing machines and clothes dryers. Compared to the shaded pole motor, these motors can generally provide much greater starting torque by using a special startup winding in conjunction with a centrifugal switch. A major appliance is a large machine which accomplishes some routine housekeeping task, which includes purposes such as cooking, food preservation, or cleaning, whether in a household, institutional, commercial or industrial setting. …

Front-loading washing machine. … A dryer or drier most commonly means: a clothes dryer / tumble-dryer a hair dryer There are also various industrial dryers for everything from wet paper to candy. … A startup winding, also known as the auxiliary winding, is used to create the torque needed to start a single phase induction motor. … A centrifugal switch is an electric switch that operates using the centrifugal force created from a rotating shaft, most commonly that of an electric motor or gasoline engine. …

Single-phase AC synchronous motors

Small single-phase AC motors can also be designed with magnetized rotors (or several variations on that idea). The rotors in these motors do not require any induced current so they do not slip backward against the mains frequency. Instead, they rotate synchronously with the mains frequency. Because of their highly accurate speed, such motors are usually used to power mechanical clocks, audio turntables, and tape drives; formerly they were also much used in accurate timing instruments such as strip-chart recorders or telescope drive mechanisms.

The shaded-pole synchronous motor is one version. A turntable is any rotating platform: a phonograph (or the platter of), for playing phonograph records (often utilised by hip hop DJs to play and mix or scratch vinyl records, such as a 45-RPM EP, see turntablism) a device used at some railroad facilities to turn a locomotive or… A tape drive, also known as a streamer, is a peripheral device that reads and writes data stored on a magnetic tape or a punched tape. … shading-coils within the magnetic circuit of the field coil Shaded-pole synchronous motors are a class of AC motor. …

Because inertia makes it difficult to instantly accelerate the rotor from stopped to synchronous speed, these motors normally require some sort of special feature to get started. Various designs use a small induction motor (which may share the same field coils and rotor as the synchronous motor) or a very light rotor with a one-way mechanism (to ensure that the rotor starts in the “forward” direction). Inertia is the tendency of any state of affairs to persist in the absence of external influences. …

Three-phase AC induction motors

For higher-power applications where a polyphase electrical supply is available, the three phase (or polyphase) AC induction motor is used. The phase differences between the three phases of the polyphase electrical supply create a rotating electromagnetic field in the motor. Three phase voltages Three phase systems have 3 waveforms (usually carrying power) that are 2/3 960; radians (120 degrees,1/3 of a cycle) offset in time. … Polyphase electrical systems supply alternating current electrical power in overlapping phases. …

There are two types of rotors in use. Most motors use the squirrel cage rotor discussed above. An alternate design, called the wound rotor, is used when variable speed is required. In this case, the rotor has the same number of poles as the stator and the windings are made of wire, connected to slip rings on the shaft. Carbon brushes connect the slip rings to an external controller such as a variable resistor that allows changing the motor’s slip rate. In certain high-power variable speed wound-rotor drives, the slip-frequency energy is captured, rectified and returned to the power supply through an inverter. A squirrel cage rotor is the rotating part commonly used in an AC induction motor. …

Several methods of starting a polyphase motor are used. Where the large inrush current and high starting torque can be permitted, the motor can be started across the line, by applying full line voltage to the terminals. Where it is necessary to limit the starting inrush current (where the motor is large compared with the short-circuit capacity of the supply), reduced voltage starting using either series inductors, an autotransformer, thyristors, or other devices are used. A technique sometimes used is wye-delta starting, where the motor coils are initially connected in wye for acceleration of the load, then switched to delta when the load is up to speed. Transistorized drives can directly vary the applied voltage as required by the starting characteristics of the motor and load. Transformers – Typical electrical configurations. … The thyristor is a solid-state semiconductor device similar to a diode, with an extra terminal which is used to turn it on. …

As in the single-phase motor, through electromagnetic induction, the rotating magnetic field induces a current in the conductors in the rotor, which in turn sets up a counterbalancing magnetic field that causes the rotor to turn in the direction the field is rotating. And just as with the single-phase motor, the rotor must always rotate slower than the rotating magnetic field produced by the polyphase electrical supply; otherwise, no counterbalancing field will be produced in the rotor. Electromagnetic induction is the production of an electrical potential difference (or voltage) across a conductor situated in a changing magnetic flux. …

This type of motor is becoming more common in traction applications such as locomotives, where it is known as the asynchronous traction motor. Traction motor typically refers to those motors that are used to power the driving wheels of a railroad locomotive, electrical multi-unit train (such as a subway or light rail vehicle train), or a tram. …

The speed of the AC motor is determined primarily by the frequency of the AC supply and the number of poles in the stator winding, according to the relation:

RPM = 2 * F * 60/p

where

RPM = (Synchronous) Revolutions per minute

F = AC power frequency

p = Number of poles, usually an even number but always a multiple of the number of phases

The torque is a function of the amount of slip, or difference in rotation, between the rotor and stator fields. Standard motors have between 2-3% slip, special motors may have up to 7% slip, and a class of motors known as torque motors are rated to operate at 100% slip (0 RPM/full stall).

The torque is determined by the amount of slip, or difference in rotation, between the rotor and stator fields.

The speed in this type of motor has traditionally been altered by having additional sets of coils or poles in the motor that can be switched on and off to change the speed of magnetic field rotation. However, developments in power electronics mean that the frequency of the power supply can also now be varied to provide a smoother control of the motor speed. Power electronics is the technology associated with the efficient conversion, control and conditioning of electric power by static means from its available input form into the desired electrical output form. …

Three-phase AC synchronous motors

As with single-phase motors, if the rotor coils of a three-phase motor are fed a separate field current to create a continuous magnetic field (or if the rotor consists of a permanent magnet), the result is a called a synchronous motor because the rotor will rotate in synchronism with the rotating magnetic field produced by the polyphase electrical supply.

A synchronous motor can also be used as an alternator. An alternator is a generator that produces alternating current by converting mechanical energy to electrical energy. …

Nowadays, synchronous motors are frequently driven by transistorized variable-frequency drives. This greatly eases the problem of starting the massive rotor of a large synchronous motor. They may also be started as induction motors using a squirrel-cage winding that shares the common rotor: once the motor reaches synchronous speed, no current is induced in the squirrel-cage winding so it has little effect on the synchronous operation of the motor.

Synchronous motors are occasionally used as traction motors; the TGV may be the best-known example of such use. The TGV is Frances train à grande vitesse; literally high-speed train. Developed by Alstom and SNCF, and operated by SNCF, the French national railway company, it connects cities in France, especially Paris, and in some other neighbouring countries, such as Belgium and Switzerland. …

Induction motors are the workhorses of industry and motors up to about 500 kW in output are produced in highly standardized frame sizes, making them nearly completely interchangeable between manufacturers (although European and North American standard dimensions are of course different).

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How electrostatics influence our lives Essay

How electrostatics influence our lives Essay.

INTRODUCTION

We all are familiar with the term electricity which comes from batteries and which is used to light bulbs, buzzers, and other electrical devices. We also know that conductors are those objects which conduct electricity easily and insulators do not conduct electricity at all. This is basic knowledge but right now we are going into detail about electricity and static electricity.

ELECTROSTATICS

Many of us have this wrong concept in our mind that insulators like plastic and wood cannot carry charges at all.

This is a wrong concept. The truth is that most insulators carry a special type of charge which conductors do not carry. The charge is created due to static electricity and is known as an electrostatic charge.

We might have heard of the term static electricity but most of the time we dismiss it as a small and unimportant part of electricity. But we are wrong; in this essay you will see the uses of electrostatics in our daily lives.

Static electricity can be produced by rubbing together two objects made of different materials. Electrons move from the surface of one object to the surface of the other if the second material holds onto its electrons more strongly than the first does. The object that gains electrons becomes negatively charged, since it now has more electrons than protons. The object that gives up electrons becomes positively charged. We experience many example of static electricity daily. For example when we close the television and then immediately put our hand on the screen, a cackling sound is produced and the hair on our hand stands up. The same thing happens when we take off a woolen sweater or when you get of your car seat.

When rubbed with each other, or with a piece of dry wool, these insulators become positively or negatively charged. The charge of the insulator depends on its affinity to electrons.

MORE AFFINITY TO ELECTRONS – BECOMES NEGATIVELY CHARGED

LESS AFFINITY TO ELECTRONS – BECOMES POSITIVELY CHARGED

Polythene

Glass Rod

Paraffin Wax

Perspex

ELECTROSTATIC INDUCTION

We have so far seen how insulators are charged by rubbing then with each other. Now we will see how insulators are charged without contact by the process of Electrostatic Induction.

When the positively charged glass rod is bought near the two connected balls, all the electrons in both the balls are attracted towards the glass rod and move to the left side (unlike charges attract). Also the remaining positively charged particles move away from the glass rod toward the right side (like charges repel). When the two balls are separated, the left one will be negatively charged ad the right one will be positively charged.

When the positively charged rod is bought close to the ball, all the electrons in the ball are attracted towards the glass rod and move to the left side (unlike charges attract). Also the remaining positively charged particles move away from the glass rod toward the right side (like charges repel). Then if we earth the right side of the ball, electrons come and neutralize the positive charges and so the ball becomes negatively charged.

Note that the balls are mounted on insulators so that they are not earthed and neutralized.

USES OF ELECTROSTATICS IN OUR DAILY LIVES

DUST PRECIPITATORS:

This is a machine used to clean the smoke produced by factories. In this smoke is passed through a meshwork of wires which are negatively charged. As the dust particles touch the wires, they get extra electrons and also become negatively charged. However the air molecules are small and stable and so they do not acquire any charge. Then as the particles move up, the negatively charged particles are attracted to positively charged metal plates fixed on the side of the box. This way the dust is removes form the dirty smoke and clean air is released.

LIGHTNING ARRESTORS:

Often you can see that on top of buildings, there is a short and sharp metal rod present which has been grounded. This is known as a lightning arrestor or conductor. It prevents lightning from touching the building and so protecting it.

When lightning (electricity) produced touches the rod, the metal rod (being a good conductor) conducts all the electricity and becomes charged. However the current keeps flowing and is grounded and neutralized.

STATIC MATS:

The main principal behind this is using the fact that air becomes negatively charged and as foot traffic or wheels pass over the surface of the mat (which is positively charged) the dirt is attracted to the mat and so it controls the cleanliness of the surroundings.

PHOTOCOPIERS:

A photocopy machine is one of the greatest inventions of man. It allows us to duplicate any piece of paper. This is how electrostatics is used to photocopy papers.

Firstly positive charge is sprayed onto the plate from a high voltage power supply. Paper is then placed through the plate and a light is shone through it. Where the paper is white, light passes though, where the paper is dark, a shadow is formed. The light falling on the white part just gives it the extra energy needed to allow the charge to escape to the earth and get grounded and thus the negatively charged ink is attracted to the dark areas, which is still positively charged. Then this is dried and given out.

PAINTING CAR PARTS:

In this process to paint car parts, the spray nozzle of the paint is connected to a negatively charged electrode and the part is connected to the positive electrode. This is why the ink is attracted towards the part. This process is better than the standard process because it gives a better finish.

COATING:

In this setup, paper or cloth is fed giving them a specific charge. Polarized grains are supplied at the other end with the opposite charge. As they approach, the polarized grains get attracted to the material as an electrical field is produced.

FACTORS AFFECTING ELECTROSTATICS

ECONOMICAL

In today’s world, no appliance can function without electricity including TV’s, computers, microwaves, music systems, etc. Producing electricity is one of the major problems faced by all the countries of the world. Nowadays due to their abundance and low cost, fossil fuels are used to turn water into steam which in turn moves turbines which move generators which create electrical energy form the kinetic energy. This is a graph of the fuel or resource used to generate electricity in the world.

This graph has been taken from

http://enrin.grida.no/htmls/tadjik/vitalgraphics/eng/graphics/e8.jpg

SOCIAL

The invention of electricity and electronic appliances has greatly affected the life of people. This has an advantage as people get entertainment from these and also use them for more efficiency in their work. But however appliances like televisions decrease our brain power and waste our time. It also makes us lazy as we sit the whole day in front of the television.

ENVIRONMENTAL

The major sources for making electricity are fossil fuels. However when fossil fuels are burnt to release energy, they release poisonous and toxic gases like Carbon Dioxide, Carbon Monoxide, and Sulphur Dioxide. This greatly pollutes the environment. Also the usage of nuclear energy leaves us with a lot of waste radioactive material which is buried in the ground and hereby pollutes the land.

CULTURAL

During cultural festivals, a lot of electricity is wasted due to the rich decorations that are done especially in marriages, receptions, famous festivals like Christmas and diwali and independence days. This wastage of electricity is a thoughtless gesture by some people and they will regret this wastage one day when generating electricity becomes very expensive.

CONCLUSION

After writing this essay, I have realized the importance of electrostatics in our lives. I have seen that electrostatics play an important role in almost every aspect of our life. One of the main concepts of electrostatics is electricity. In today’s world, no electricity will lead to a total failure and man will go back to the Stone Age. This is why we must all try our best to conserve and not to waste electricity as it is a gift to mankind. We must also use this great gift wisely and not misuse it.

BIBLIOGRAPHY

Textbook – Complete Physics Singapore Edition

Publisher – Oxford University Press

Year – 2000

Author – Stephen Pople

Textbook – Explaining Physics GCSE Edition

Publisher – Oxford University Press

Year – 1995

Author – Stephen Pople

Website – www.wikipedia.com

Encyclopedia – Microsoft Encarta Encyclopedia Deluxe 2004

How electrostatics influence our lives Essay