Lecture 3 - ECE 201, Lecture 3 Resistance, Ohm's Law,...

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1 ECE 201, Lecture 3 Resistance, Ohm’s Law, Power, Dependent Sources Please take advantage of the TA help room (EE 26). Please feel free to email me should you have questions. Office hours MWF 8:30 – 9:30AM EE 252 Announcements
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2 Summary of Lecture 2 Direct current (dc) and alternating current (ac) What is Electric energy and power? What is Voltage? Energy Conversion The relationships among voltage (V), current (I) power (P) and energy (W) Sources
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3 DC: i(t)=constant We assign a direction of current flow for the purpose of analysis only. +: flows along the direction we specified -: flows opposite to the direction we specified i(t) always opposite to the direction of electron motion. t i 5A -1A Alternating current (AC or ac) Direction and amplitude change periodically with time. A fundamental form of AC current is i(t)=A sin ( ϖ t + φ ) Peak value Frequency Phase
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4 Ideal voltage source Ideal battery or dc voltage source: V o Circuit V o V I(A) Voltage drop is V o (> 0) from long dash side to short dash side. An ideal battery can deliver constant voltage regardless of current drawn by the circuit. An escalator carries the balls back to a certain height
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5 Ideal voltage source: - + + - Circuit Circuit -v(t) v(t) Circuit Circuit i(t) -i(t) Ideal current source: Supplies voltage v(t) regardless of circuit currents Supplies current i(t) regardless of circuit voltages
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6 Voltage is the difference between electric potentials Charges flow from high energy locations to low energy locations. We really want to show the electrical energy at different location of a circuit. But we don’t know the amount of charge at each location in general, so what we do? Define: It is the potential difference (or voltage across an element) that drives current. Can define ground (U=0) at any point of the circuit 1 2 12 W W W U and V q q - = =
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Definition of Voltages B V x + + - - A V y A B + - V AB V +- 5 2 V AB = – V BA , V 25 = – V 52 V 1 = V + – = – V – + V 1 V AB = – V BA , V x = V
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This note was uploaded on 02/13/2012 for the course ECE 201 taught by Professor All during the Fall '08 term at Purdue University-West Lafayette.

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Lecture 3 - ECE 201, Lecture 3 Resistance, Ohm's Law,...

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