Ohms law Essay Example for Free

Ohms law Essay An electronics factory needs resistors of 5 ohms and 15 ohms for a new electrical device. My task is to investigate how the resistance of a piece of wire depends on length and to find the length of the wire needed to make the required resistors, using only 4 volts. Introduction/Planning A selection of different wires made from constantan and nichrome and the usual laboratory apparatus will be available for me. Wire A Constantan wire of approximate diameter 0. 3mm Wire B Constantan wire of approximate diameter 0. 4mm Wire C Constantan wire of approximate diameter 0. 3mm A constantan is an alloy whose resistance stays fairly constant when it becomes hot. In fact the resistance changes by less than 0. 5% even when the temperature rises by a few hundred degrees. Nichrome, along with other metals, is an alloy whose temperature does change appreciably when it becomes hot. Before starting my coursework, I have to find the variables in the experiment, safety aspects etc. I found that a number of things affect the resistance of a wire. Below is a list of factors and reasons why they affect the resistance of a wire. From this list of factors I have to make sure that these factors remain constant or excluded from the experiment. We are only investigating length but the other variables may change our outcomes. In electricity, resistance is the ratio of the potential difference (p. d. or voltage) across a conductor to the electrical current, which flows through it as a result. The unit of measurement is the ohm (O), this being the resistance of a conductor requiring a potential difference of 1 volt across its ends to produce a current of 1 ampere. For a given metal conductor at constant temperature the value is the same whatever the current (Ohms law), but rises if the temperature rises. Any conductor possessing resistance gives off heat when a current flows through it. Joules law describes this effect. Resistance occurs when the electrons travelling along the wire collide with the atoms of the wire. These collisions slow down the flow of electrons causing resistance. Resistance is a measure of how hard it is to move the electrons through the wire. Ohms law: The current flowing through a metal is proportional to the potential difference across it, provided that the temperature remains constant. We are going to use metals, which obey ohms law, metals which give us a constant value for resistance (gradient). Resistance (? ) = P. d across the wire (V) / Current through the wire (A) Current flows in an electric circuit in accordance with several definite laws. The basic law of current flow is Ohms law, named for its discoverer, the German physicist Georg Ohm. Ohms law states that the amount of current flowing in a circuit made up of pure resistances is directly proportional to the electromotive force impressed on the circuit and inversely proportional to the total resistance of the circuit. The law is usually expressed by the formula I = V/R, where I is the current in amperes, V is the electromotive force in volts, and R is the resistance in ohms Ohms law applies to all electric circuits for both direct current (DC) and alternating current (AC), but additional principles must be invoked for the analysis of complex circuits and for AC circuits also involving inductances and capacitances. A series circuit as on page 5, is one in which the devices or elements of the circuit are arranged in such a way that the entire current (I) passes through each element without division or branching into parallel circuits. When two or more resistances are in series in a circuit, the total resistance may be calculated by adding the values of such resistances. If the resistances are in parallel, the total value of the resistance in the circuit is given by the formula: In a parallel circuit, electrical devices, such as incandescent lamps or the cells of a battery, are arranged to allow all positive (+) poles, electrodes, and terminals to be joined to one conductor, and all negative (-) ones to another conductor, so that each unit is, in effect, on a parallel branch. The value of two equal resistances in parallel is equal to half the value of the component resistances, and in every case the value of resistances in parallel is less than the value of the smallest of the individual resistances involved. In AC circuits, or circuits with varying currents, circuit components other than resistance must be considered. If a circuit has a number of interconnected branches, two other laws are applied in order to find the current flowing in the various branches. These laws, discovered by the German physicist Gustav Robert Kirchhoff, are known as Kirchhoffs laws of networks. The first of Kirchhoffs laws states that at any junction in a circuit through which a steady current is flowing, the sum of the currents flowing to the point is equal to the sum of the currents flowing away from that point. The second law states that, starting at any point in a network and following any closed path back to the starting point, the net sum of the electromotive forces encountered will be equal to the net sum of the products of the resistances encountered and the currents flowing through them. This second law is simply an extension of Ohms law. The application of Ohms law to circuits in which there is an alternating current is complicated by the fact that capacity and inductance are always present. Inductance makes the peak value of an alternating current lag behind the peak value of voltage; capacitance makes the peak value of voltage lag behind the peak value of the current. Capacitance and inductance inhibit the flow of alternating current and must be taken into account in calculating current flow. The current in AC circuits can be determined graphically by means of vectors or by means of the algebraic equation, in which L is inductance, C is capacitance, and f is the frequency of the current. The quantity in the denominator of the fraction is called the impedance of the circuit to alternating current and is sometimes represented by the letter Z; then Ohms law for AC circuits is expressed by the simple equation I = V/Z. We know that all instruments have an error on its measurement, so the way to work out the percentage error is: Percentage error = (error / measured value) i 100 Conduction in metals In metals, atoms contain protons, nucleus and lose electrons which orbit around the nucleus. Below, I have investigated conduction in metals and how they affect resistance. METAL LATTICE (Electrons move in a random direction. ) METAL LATTICE (Electrons with power pack in a particular direction. ) Variables Length: If the length of the wire is increased then the resistance will also increase as the electrons will have a longer distance to travel and so more collisions will occur. Due to this, the length increase should be proportional to the resistance increase. Thickness: If the wires thickness is increased the resistance will decrease. This is because of the increase in the space for the electrons to travel through. Due to this increased space between the atoms, there should be fewer collisions. The number of free electrons changes from one material to another. The size of the ions changes from one material to another, this affects the current and therefore affects the resistance. The arrangement and size of the atoms change from one material to another. So if there is a kink in the wire this will change the thickness of the wire. Temperature: If the wire is heated up the atoms in the wire will start to vibrate because of their increase in energy.

A Young Americans Discovery of the Silent Majority Essay -- Essays P

A Young American's Discovery of the Silent Majority History panders to the glorious and dramatic while often there is a story untold. Perhaps it is less exciting, but no less crucial in understanding history as a whole. Thus is the story of the â€Å"silent majority.† On November 3rd 1969, one year after his victory in the United States Presidential race, President Nixon issued an address to the American public in which he coined the term â€Å"silent majority.† President Nixon’s address began by describing the situation he inherited when taking office. Nixon described the situation as such: â€Å"The war had been going on for four years. One thousand Americans had been killed in action. The training program for the South Vietnamese was behind schedule; 540,000 Americans were in Vietnam with no plans to reduce the number. No progress had been made at the negotiations in Paris and the United States had not put forth a comprehensive peace proposal. The war was causing deep division at home and criticism from many of our friends as well as our enemies abroad (Episode).† President Nixon then proceeded to detail the progress made and the different actions taken by his administration throughout the course of the first year of his first term. Nixon described the pressure on his administration to end the war. He referred to a protest in San Francisco in which Protesters carried picket signs donning the clause, â€Å"Lose in Vietnam, bring the boys home!† To this President Nixon responded: â€Å"Well, one of the strengths of our free society is that any American has a right to reach that conclusion and to advocate that point of view. But as president of the United States, I would be untrue to my oath of office if I allowed the policy of this nati... ...speech/ >. Freed, Kenneth J. "Kissinger Interview." Associated Press featured in Albany Student Press. 6 Feb. 1973 Frost, Michell. "On the Other Hand." Albany Student Press. 4 Dec. 1970. Frost, Mitchell. "View From the Right." Albany Student Press. 30 Jan. 1973 Oringher, Maida. "Misplaced Priorities." Albany Student Press. 25 Jan. 1972. Pyle, Richard. "Vietnam's New Map." Associated Press featured in Albany Student Press. 31 Oct. 1972. Rosten, Leo. A Trumpet For Reason. Garden City, NY: Doubleday &Company Inc, 1970. The Tactical Leadership. "SUNYA Protests." Albany Student Press. 25 Jan 1972 Weintraub, Peter. "Vietnam Vets: America's Most Alienated." Albany Student Press. 20 Oct. 1972. Whistle, Gary. Interview with Amanda May Whistle. 25 April 2005 Wire Services Compilation. "Rocky Supports Nixon." Albany Student Press. 25 Jan 1972.

Wizard of Oz

Wizard of Oz Interpretation The Wonderful Wizard of Oz is a story about a girl named Dorothy who experiences a cyclone that takes her to a magical land of good and bad. When she is in this land she encounters a Scarecrow, Tin Man, and a Lion. These 3 characters are with her throughout the story and they go through different tough situations together. In the end they make their way to the Oz who grants their wishes and Dorothy goes back home. People say that this story is based off of populism, money reforms, and a political movement led by William Jennings Bryan.The Wonderful Wizard of Oz is not intentionally written to be linked to the way the economy was because it is a children’s book, it is a made up story, and Baum, the author of the book, never stated that it was. In the article â€Å"The Story Behind The Wonderful Wizard of Oz† it explains how L. Frank Baum and William Jennings Bryan’s concern was the nature of the money supply then prevalent in the United States, and in the Mid-Western States in particular. Baum was featured in a movie called The Dreamer of Oz that showed how each character was thought of and how he had put the story together.For example, Dorothy was the name of a sweet little niece that he had which is how Dorothy from The Wonderful Wizard of Oz came about. Each character from the book was represented as someone that he had come across in his life at some point in time. In The Dreamer of Oz it shows how Baum enjoyed telling stories to his children and to the other kids that could come along. His wife would always bring it up to him that he needs to put it into the form of a book. Baum being the stubborn guy he was never really considered it.Sooner or later he finally realized that it all made sense and it all pieced together to become a story with no title. Baum sat down with his wife and mother in law and asked them for their opinion on what he should name the story. This is how the title of The Wonderful Wizard o f Oz came about. Therefore Baum had written the book from experiences and people from his past not because of the way the economy was ran in the 1900s. Last but not least Baum never stated that his story was written to represent populism.In the article â€Å"The Story Behind The Wonderful Wizard of Oz† it explains how each character in the children’s book is represented by a problem that was occurring. For example, the Scarecrow is represented as the farmers and the Tin Man is represented as industrial workers. In the article it states that â€Å"Baum and Bryan wanted money to be based on silver, not gold, as silver was readily available in the Mid-West, where it was mined. Such a money supply could not be manipulated by the banks. Then from there it goes into explaining each part of the story and they link together. Just because Baum and Bryan had these views on the economy does not necessarily mean that he wrote this story secretly about it. In conclusion, The Wonde rful Wizard of Oz is not intentionally written to be linked to the way the economy was because it was written as a children’s book, it is a generally made up story that Baum had based off of his lifestyle, and he never stated that it was intentionally written about the ways of being in the 1900s.

Brief Description Of Edward Teller Essay - 539 Words

Edward Teller Edward Teller is a Hungarian-American physicist, known for his work on the hydrogen bomb. Teller was born in Budapest in 1908, and was educated in Germany at the Institute of Technology in Karlsruhe and at the universities of Munich and Leipzig. He received his Ph.D. in physics in 1930. After working at the University of Goettingen with James Frank and at the Niels Bohr Institute, he became Professor of Physics at the George Washington University in Washington, D.C. in 1935. In 1941 he became an American citizen. In the same year he joined the U.S. atomic bomb development project known as the Manhattan Project. For more than a decade he worked with the Italian-born physicist Enrico Fermi on this and succeeding projects at†¦show more content†¦In 1952 he became professor of physics at the University of California, Berkeley, and director of the Livermore, California, division of the universitys radiation laboratory (now Lawrence Livermore National Laboratory). He was the princ ipal architect of the hydrogen bomb, first tested in 1952, and he strongly advocated that the United States continue the testing of thermonuclear weapons. He also made contributions to the application of nuclear explosives to peaceful uses. From 1954 to 1958, he served as Associate Director at the new Lawrence Livermore Laboratory. He became a consultant to the laboratory in 1952. In 1975 he retired from teaching, but remained director emeritus of the radiation laboratory. After working on the production of the atomic bomb in the Manhattan Project, Edward Teller went on to become the principal designer of the hydrogen bomb. He remained a steadfast advocate of nuclear weapons testing throughout his life. In recent years, Teller has championed the ``Star Wars missile defense system, despite the fact that such a system is very expensive and has no conceivable way of working. Teller has written a few books. 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