E17 summary

# E17 summary - ENG17 Summary Review Spring 2011 Prof Spencer...

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ENG 17 Introducetion, Prof. Spencer, Spring 2011 1 ENG17 Summary & Review Spring 2011 Prof. Spencer Four Fundamental Quantities Four fundamental quantities: charge, flux linkage, current, voltage Charge is a fundamental property of some matter: electrical forces result from charge separation Flux linkage is the integral over time of voltage and is caused by the interaction between magnetic fields and moving charges Current is the flow of electric charge Voltage is electrical potential energy per unit charge. Separating charge yields an electric field (to describe the force) and voltage is the integral of the field over distance

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ENG 17 Introducetion, Prof. Spencer, Spring 2011 2 Four Fundamental Quantities Although not unique, you can think of electronics as involving relationships between these four fundamental quantities: charge, flux linkage, voltage and current There are six possible relationships between pairs of these four quantities: The memristor is a new element that may be important in the future, but it is not in your book! Power and Energy Power is the derivative of energy with respect to time (i.e., it is the rate of exchange of energy) Remembering that voltage is electrical potential energy per unit charge, we find where we have assumed that the voltage is constant over time and have recognized that current is the time-derivative of charge Power is measured in Watts P = dU el dt = d QV ( ) dt = V dQ dt = VI
ENG 17 Introducetion, Prof. Spencer, Spring 2011 3 Water Models – Battery Our water models will use: Pressure analogous to voltage Electric current is analogous to water flow If a motor with constant torque drives a turbine (i.e., an enclosed paddle wheel), there will be a constant pressure difference between the water entering and the water leaving the turbine independent of the flow This is a “battery” for our water models Water Models - Resistor One possible water model for a resistor is simply a pipe with a narrow region to restrict the flow We are assuming with these models that the pipes are completely full of water and that the flow is laminar (so that flow is proportional to pressure drop) In real pipes, the flow is rarely laminar – so water in pipes is usually more complex than electric current in wires!

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ENG 17 Introducetion, Prof. Spencer, Spring 2011 4 Kirchoff’s Voltage Law (KVL) If you sum all of the voltage rises and drops around any loop, the total must be zero Think about walking around Kemper Hall up and down different stairs, but returning to the same point The signs are arbitrary mathematically, but meaningful physically () 123 B VV V V I RRR = ++ =+ + 9 V 1 mA 9 k B V I == = Ω 0 B −−= Kirchoff’s Current Law (KCL) The sum of all currents entering, or leaving, a node must be zero Think of water in pipes
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E17 summary - ENG17 Summary Review Spring 2011 Prof Spencer...

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