EE 2006 Electric Circuit Analysis Spring January 23, 2015 Lecture 02

Transcription

1 EE 2006 Electrc Crcut Analyss Sprng 2015 January 23, 2015 Lecture 02 1

2 Lab 1 Dgtal Multmeter Lab nstructons Aalable onlne Prnt out and read before Lab MWAH 391, 4:00 7:00 pm, next Monday or Wednesday (January 26/28) Work n pars (group of 3 f odd number) Group data, nddual report Lab safety rules 2

3 Lecture Outlne Voltage, power, and energy Acte and passe elements Ohm s Law Krchhoff s current and oltage laws 3

4 Reew: Electrc Current Created by moton of charge I Measured by charge change rate, unt n A (amperes) dq dt, 1A 1C 1s Conenton on drecton: flow drecton of poste charges, opposte to the flow of negate charges 4

5 Reew: DC Current and AC current Drect current (DC) Alternatng current (AC) I DC ( I ): current that remans constant wth tme AC ( ): current that ares snusodally wth tme 5

6 Voltage Defnton: electrcal potental dfference between two ponts of an electrc crcut or electromote force (emf) requred to moe the charge from one pont to another pont a ab b The potental dfference between ponts a and b: ab a b dw/dq, w: energy wth unt n joules (J) q: charge wth unt n coulombs (C) : oltage wth unt n olts (V) 1V1J/C Polarty: or used to defne the reference drecton Voltage drop drecton: from polarty to polarty The polarty can be defned by you 6

7 Power and Energy Power: the tme rate of expendng or absorbng energy, measured n watts (W): pdw/dt(dw/dq).(dq/dt) Sgn conenton: a b Current drecton s the same as the oltage drop drecton, P When current drecton s opposte to the oltage drop drecton, P a b 7

8 Crcut Elements Crcut element s a mathematcal model of a real dece Acte element: p <0, generatng energy.e., batteres, generators, operatonal amplfers Passe element: p>0, absorbng or storng energy.e., resstors (absorbng energy), capactors and nductors (storng energy) 8

9 Acte Element The most mportant acte elements are oltage and current sources Independent sources Dependent sources V Independent oltage sources Independent current sources Dependent oltage source, VCVS or CCVS Dependent current source, VCCS or CCCS 9

10 Example of Dependent Sources A B A 10 C 5V C 0.2 CCVS CCCS 10

11 Resstance Resstance s the physcal ablty to resst current. The crcut element used to model ths behaor s the resstor, whch s a passe element Crcut symbol: R Unt for R: Ω, 1Ω 1V/A A: crosssectonal area n m 2 l: length n m Resstance s dependent on the materal property and physcal dmensons of the resstor ρ: Materal receptty n Ω m A R l ρ 11

12 Ohm s Law Statement: the oltage across a resstor s drectly proportonal to the current flowng through the resstor,.e., R V R 12

13 Short Crcut and Open Crcut R ( 0 R < ) (A)Short Crcut (SC) R 0 0 (B) Open Crcut (OC) R 0 0 R0 0 R 13

14 Conductance Conductance G s the recprocal of resstance R,.e., G 1 R Unt of G: semens (S) or mhos ( ) 1S1/Ω1A/V 14

15 Power Power: the tme rate of expendng or absorbng energy, measured n watts (W): pdw/dt(dw/dq).(dq/dt) Instantaneous power for any crcut element: p(t)(t)(t) The power delered to a resstor s p p R ( R) 2 2 R R 2 G 2 G 15

16 Branch, Nodes and Loops One node A branch s a sngle element such as a oltage (current) source or a resstor; A node s the pont of connecton between two or more branches; A loop s any closed path n a crcut 16

17 Elements n Seral and Parallel Two elements are n seres f they exclusely share a sngle node Two elements are n parallel f they are connected to the same two nodes 17