Basic EE Definitions Units Conventions and Circuit Elements

Basic EE Definitions, Units, Conventions, and Circuit Elements Volts, Current, Energy, Power, Sign Conventions, and Sources Kevin D. Donohue, University of Kentucky 1

Unit Prefixes pico (p) Ø nano (n) 10 -9 Ø micro ( ) 10 -6 Ø milli (m) 10 -3 Ø 10 -12 kilo (k) 103 Ø mega (M) 106 Ø giga (G) 109 Ø tera (T) 1012 Ø Kevin D. Donohue, University of Kentucky 2

Basic Definitions Ø Ø Ø Electric Circuit - an interconnection of electrical components through which charge can be moved. Current - the rate of change of charge with respect to time (coulombs per second). 1 Ampere = 1 coulomb per second. 1 Volt = 1 joule per coulomb = 1 newton-meter per coulomb. 1 Watt = 1 Ampere-Volt = 1 joule per second Kevin D. Donohue, University of Kentucky 3

Flow Conventions Ø Ø Ø Positive current denotes the direction of positive charge. Describe the direction of charge in both circuits. Indicate which elements are supplying and which are absorbing energy. I 1=2 A B I 2=-1 A Kevin D. Donohue, University of Kentucky B 4

Math Notation and Relationships Ø Current, charge, and time Ø Voltage, energy, and charge Ø Voltage, current, and power Ø Power supplied equals power absorbed for all elements in a circuit. Kevin D. Donohue, University of Kentucky 5

Passive Sign Convention Ø Ø Ø It is assumed that positive charge entering the positive terminal of an element implies power absorbed by the element. Therefore, charge leaving the positive terminal of an element implies power supplied or delivered by the element. If the words absorbed or supplied are not given with a power value, power absorbed will be assumed. Kevin D. Donohue, University of Kentucky I V 6

Example Problems Ø A 10 volt battery is connected to a 20 watt light bulb for 30 minutes. How much charge is lost from the battery? Ø 5 coulombs of charge pass from point A to point B at a constant rate. If 100 joules is absorbed, what is the voltage across AB? Kevin D. Donohue, University of Kentucky 7

Independent Sources Ø Independent sources can deliver power in a circuit. An ideal source will have either a fixed voltage OR current independent of other elements in the circuit. i(t) + v(t) _ + V _ Kevin D. Donohue, University of Kentucky 8

Power Delivered/Absorbed Examples Ø Find the power absorbed in each element assuming the passive sign convention a I c I + V V + b V I d V I a 1) I = 2 A, V = 3 V a 2) I= -1 A, V = 4 V b 1) I = 6 A, V = -2 V b 2) I = -2 A, V = -9 V c 1) I = 7 A, V = 1 V c 2) I = -3 A, V = -2 V d 1) I = 1 A, V = -1 V d 2) I = -2 A, V= 6 V Kevin D. Donohue, University of Kentucky 9

Power Circuits Ø Ø In a circuit power delivered must equal power absorbed over all elements. Find power delivered and absorbed in each element. - 6 V + 1 0. 5 A 1 A + 2 18 V - 1 + - 5 V Kevin D. Donohue, University of Kentucky + 2 1 V - 10

Dependent Sources Ø Dependent sources can deliver power in a circuit. The voltage or current of a dependent source depends on the current or voltage in other circuit elements. CCCS CCVS F(i 1) + H ( i 1 ) - VCCS VCVS G ( v 1 ) Kevin D. Donohue, University of Kentucky + E ( v 1 ) 11

Circuit Examples Ø Find power absorbed/supplied by each element in the circuit. + 11 V - + 6 V 1 0. 5 A i 1 2 + 1 V 3 + 5 V 4 i 1 - Kevin D. Donohue, University of Kentucky -0. 5 A 12