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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 particle’s 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 Δ 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
 Electric charge, Prof. Spencer

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