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Unformatted text preview: ENG 17 Introducetion, Prof. Spencer, Spring 2011 1 ENG17 Introduction Spring 2011 Prof. Spencer What is Engineering? Engineering is the art of applying your knowledge of science and mathematics to solve problems mathematics is the handmaiden to engineering! We will solve differential equations, but that is not the point of this class Solving problems involves, among other things, modeling the problem at a level that contains sufficient detail, but still allows the designer to understand the problem well enough to develop or apply intuition Different levels of modeling are often called levels of abstraction solving a problem is often much easier if you choose the appropriate level of abstraction (e.g., lumpedcircuit approximation) ENG 17 Introducetion, Prof. Spencer, Spring 2011 2 ENG17 Topics We will be covering basic electric circuits in some detail, but much of the material is useful for, or analogous to, material in other engineering disciplines developing models of real physical systems that enable us to analyze them quantitatively developing the ability to think about what the mathematics means (it must represent something real or it has no purpose in engineering) many mechanical and electrical systems are analogous and some things are much easier to visualize in one or the other this material is on the EIT/FE exam DC Circuits Outline Charge, Force, Electric Field, and Energy Voltage Four fundamental quantities: charge, flux linkage, current, voltage The Atom Conductors and Resistors Electric Current Power and Energy Schematics & models Definitions ENG 17 Introducetion, Prof. Spencer, Spring 2011 3 Charge Distribution Consider a spatial distribution of charges: Negative Charge Positive Charge Test Charge Consider a spatial distribution of charges Now consider a test charge, q Negative Charge Positive Charge Test Charge ENG 17 Introducetion, Prof. Spencer, Spring 2011 4 Force There is a force on this test charge it is attracted by the charges of opposite sign it is repelled by the charges with the same sign Negative Charge Positive Charge Test Charge Force Electric Field We can visualize this force by saying that there is an Electric Field in the region, then if the electric field is E , the force on the test charge is F = qE Negative Charge Positive Charge F Electric Field ENG 17 Introducetion, Prof. Spencer, Spring 2011 5 Work & Energy Work is equal to force times distance if the force is constant (if the force varies we integrate) The work done in moving some particle is equal to the change in the particles energy Consider lifting an object off of the floor; the gravitational force is approximately constant ( mg ), so the work done in lifting to a height h is mgh Equating the work done with the change in the gravitational potential energy of the particle, we say the change in potential energy is U g = mgh (we often choose a zero reference, e.g. the floor, in often choose a zero reference, e....
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 Fall '08
 Lagerstrom

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