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Unformatted text preview: Chapter 1: Electric Circuit Theory EECE312 Electronics Dr. Walid Kamali Fall 2007 Outline Voltage, Current, Power, Resistors, Sources Circuit Analysis Techniques Inductors, Capacitors DC, Intro to time domain response AC, Sinusoids, Phasors, Transformers Voltage and Current & Energy The concept of electric charge is the basis for describing all electrical phenomena. 1. The charge is bipolar, meaning that electrical effects are described in terms of positive and negative charges. 2. In circuit theory, the separation of charge creates an electric force (voltage), and the motion of charge creates an electric fluid (current). 3. Whenever positive and negative charges are separated, energy is expended. Active and Passive Elements An active element is one that models a device capable of generating electric energy. Passive elements model physical devices that cannot generate electric energy. Resistors, inductors, and capacitors are examples of passive elements. Ideal Independent Sources The circuit symbols for the ideal independent sources are as shown. Note that a circle is used to represent an independent source. To completely specify an ideal independent voltage source in a circuit, you must include the value of the supplied voltage and the reference polarity. Dependent Sources As for the dependent sources, both the dependent current and voltage sources maybe controlled by either a current or a voltage elsewhere in the circuit, so there are a total of four variation. a. Voltagecontrolled voltage source b. Currentcontrolled Voltage source c. Voltagecontrolled current source d. Currentcontrolled current source Kirchhoffs Laws There are two Kirchhoffs laws: Kirchhoffs current law (KCL) and Kirchhoffs voltage law (KVL) Kirchhoffs Current Law KCL: At any instant of time, the sum of currents entering a node is equal to the sum of currents leaving the node . At node N, for example, KCL gives: i A + i B = i C + i D . Alternatively, i A + i B i C i D = 0, where currents flowing towards a node have been arbitrarily assigned a positive sign, which means that currents flowing away from a node should be assigned a negative sign. N i A i C i B i D Kirchhoffs Voltage Law KVL: A t any instant of time, the sum of the voltage rises around any loop is equal to the sum of the voltage drops around the loop. or A t any instant of time, the algebraic sum of the voltages around any loop is zero , since voltage drops and voltage rises are assigned opposite signs v 1 v 5 v 2 v 4 v 3 q + + + + + + Ohms Law For purposes of circuit analysis, we must reference the current in the resistor to the terminal voltage. The relationship between the voltage and the current is: v = R i Where v = the voltage in volts, i = the current in amperes, and R = the resistance in ohms (). Electrical Resistance and Conductance Resistance is the capacity of materials to impede the flow of current or...
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This note was uploaded on 02/07/2011 for the course EECE 312 taught by Professor Walidkamali during the Fall '07 term at American University of Beirut.
 Fall '07
 WalidKamali
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