es3_lab3 - Tufts University School of Engineering...

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Tufts University School of Engineering Department of Electrical and Computer Engineering ES3 - Introduction to Electrical Circuits Fall 2007 Lab Section: Friday 2:30-4:30pm Experiment 3 Thevenin Equivalent Circuits and Maximum Power Transfer Name: Teddy Portney Edward . Portney@ tufts . edu Submitted to: Bertan Hallacoglu Experiment Performed: October 25, 2007 Experiment Due: November 2, 2007
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I. PURPOSE The purpose of this lab was to learn how to create Thevenin equivalent circuits for complex laboratory devices, such as a function generator, a 9-volt battery, and even a microphone. As creating theoretical Thevenin equivalent circuits was discussed in lecture, it is useful to also know how to measure the properties needed to find the equivalent circuit experimentally. This lab also dealt with the concept of maximum power transfer, an idea, which goes hand in hand with the Thevenin equivalent circuit. II. INTRODUCTION A Thevenin equivalent circuit is a model of a real circuit. Its purpose is to simplify extremely complicated circuits that would otherwise be difficult or even impossible to solve into a circuit that only contains two elements. Specifically, it is possible to model the function generator as a Thevenin equivalent circuit. The function generator in all likelihood consists of many different components, at least several of which have not even been mentioned in lecture. However, through experimental measurements using a voltmeter and an ohmmeter, it is possible to reduce the function generator to a circuit that consists of solely a voltage source and a Thevenin resistance. The basic design of a Thevenin equivalent circuit is shown in the appendix of this lab report. This concept of reducing complex circuits into circuits that behave in exactly the same manner is very useful. For example, because the Thevenin equivalent circuit for a function generator is so easy to find, it is completely unnecessary to know the actual schematic for the function generator in order to perform basic calculations. Thevenin equivalent circuits also allow for modeling of devices that are not actually complex circuits, or even circuits at all. The example of this used in this lab was using a 9-volt battery and creating a Thevenin equivalent circuit based on certain measurements taken. As mentioned above, this lab also brought in the idea of maximum power transfer. This is very useful, like the Thevenin equivalent circuits, because for one set Thevenin equivalent circuit you can calculate what load must be connected to it in order to deliver the maximum power. As can be shown by Ohm’s Law, power is equal to voltage times current, and is therefore equal to current squared times the resistance. P = V 2 / R, and P = I 2 * R. As one can see in these formulas, neither a short circuit, which provides maximum current, nor an open circuit, which provides maximum voltage drop, will provide the maximum power. In fact, both of these cases will provide a power of 0 Watts.
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This note was uploaded on 03/27/2008 for the course ES 3 taught by Professor A during the Fall '08 term at Tufts.

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es3_lab3 - Tufts University School of Engineering...

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