20005 - chapter01 snuengineering.snu.ac.kr/lecture_pdf/ee/2005 - chapter01_snu.pdf · microsoft...
TRANSCRIPT
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• Electricity – From the word “Elektron”– Greek for “amber”
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Electrical systems have two main objectives:
• To gather, store, process, transportinformation & Energy
• To distribute and convert energy
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Electrical Engineering Subdivisions
Communication Computer Systems Control Systems Electromagnetics
Electronics Power Systems Signal Processing
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Where do we find electrical circuits?• Communications
– Radio, internet, telephone, television• Data Processing
– Desktop computers, servers• Automobiles
– displays, sensors, motors• Home
– lighting, heating, appliances• Weather Stations
– wind speed, precipitation, temperature• Power Plants
– moving magnets, transformers
Human Body is Polymeric System controlled by Electrical System?
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Why Study Electrical Engineeringin SNU MSE ?
• To know the Basic Knowledge of Electronics • So you can understand a little about Electronic
System around you • To Operate and Maintain Electrical Systems• To Communicate with Electrical Engineer • Additionally Good Examination Grade
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Basic Definitions
Capacitor dtdVCI = 2
21 CVP =
Power
ResistorRVIorIRV ==
InductordtdILV =
Passive Component
Active ComponentDiode
TransistorOP amp
Passive : No Power Gain (Two terminal)Active : Power Gain : Built-in Power Source
Linear
NonLinear
221 LIP =
RVIRVIP
22
21 ===
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Circuit Symbols• Battery or Power Supply• Resistor• Capacitor• Switch
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More Circuit Symbols
• DC Voltage Supply• AC Voltage Supply• Open Circuit• Closed Circuit• Short Circuit • DC Current Supply• AC Current Supply
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Electrical Current • Current - the rate of flow of charge through a
conductor– Conventional Current
• Direction of flow of positive (+) charges
– Electron Current• Opposite to that of conventional current
• Units for Current– Amperes
• Charge of the Electron– e = -1.603 × 10-19 Coulombs
• 1 A = 1 C/s
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Effect of Electric Currents on the Body
• 0.001 A can be felt• 0.005 A is painful• 0.010 A causes involuntary muscle contractions• 0.015 A causes loss of muscle control• 0.070 A can be fatal if the current last for more
than 1 second
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Current Equation
tqi∆∆
=
Current in Amperes (A)
Charge inCoulombs (C)
Time in Seconds (s)
dt)t(dqi =Calculus:
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Figure 1.4
dttdqti )()( = (1.1)
∫ +=t
ttqdttitq
0
)()()( 0(1.2)
)(tq : Charge
)(ti : Currentt0 : some initial time
at which the chargeis known
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Types of Electricity
• Static Electricity - no motion of free charges• Current Electricity - motion of free charges
– Direct Current (DC)– Alternating Current (AC)
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Voltage Description
Current Description
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KIRCHHOFF’S CURRENT LAW (KCL)
• The net current entering a node is zero.• Alternatively, the sum of the currents entering a
node equals the sum of the currents leaving a node.
i1 + i2 - i3 = 0 i3 - i4 = 0 i5 + i6 - i7 = 0
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Kirchoff Current Law : Σ Ik=0“The sum of current at a node is always zero”
Parallel Circuit : Constant Voltage
∑∑ ===k kk k Z
ZZV
ZVI 1
Resistor ∑=k
kRR /1 Capacitor ∑=k
kCC
ia - ib + ic - id = 0
Σ Ik=0
Current Direction+ : Inward Direction- : Outward Direction
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ia = 4A ib = -2A ic = -8A
ia = ib = ic
Examples of KCL
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Voltage • Voltage : A measure of the potential to move electrons.• Sources of Voltage
– Batteries (DC)– Wall Outlets (AC)
V9)t(v =
)t120sin(V110)t(v π=
Unit of voltage : Volts (V) 1V = 1 Joule per coulomb (J/C).
DC
AC
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baab vv −=
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KIRCHHOFF’S VOLTAGE LAW(KVL)
The algebraic sum of the voltages equals zero for any closed path (loop) in an electrical circuit.
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Kirchoff Voltage Law : Σ Vk=0“The sum of voltage drop around a loop is always zero”
Serial Circuit : Constant Current
∑∑ ===k
kk
k ZZIZIZV
Resistor ∑=k
kRR Capacitor ∑=k
kCC /1
Same Current for All Elements Same Volatve for All Elements
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A, B C D, E, F
Parallel
Serial
Rearrangement of Circuit
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Power and Energy
• Power : the rate of energy conversion• Units : Watts• Equation : p=iv
• Resistors convert electrical energy into heat energy.
p = iv Power delivered by a batteryp = -iv Power dissipated by a resistor
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POWER AND ENERGY
)()()( titvtp =
vip =
2Rip =
Rvp
2
=
∫=1
2
)(t
tdttpw
Power
Energy
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Introduction to Circuit Element- Conductor- Voltage Source- Current Source- Resistor
Ideal Element :
Conductor : The voltage between ends of an ideal conductor is zero regardless of the current through the conductor
Short Circuit
Note. Open Circuit
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Independent Source
Voltage or Current is specified by itself into Circuit.
Constant Voltage Source Constant Current Source
Battery, Home Power Specially Designed Circuit
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Dependent Voltage Source
Voltage or Current is determined by others in Circuits
Τransistor, Amplifier, Electrical Generator
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Dependent Current Source
Current through Source is designed as 3vx
if vx = 5V Source : 15A
Many type of real world devices such as Electrical machines Transistor, transformer Amplifierdue to Safety & Economics
Current through Source is designed as 2iy
if iy = 5A Source : 10A
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Resistor Equations
• Ohm’s Law: v = iR• Resistance:
ALR ρ
=
Resistivity in Ohms-meters (Ω m)
Cross-sectional AreaIn square meters (m2)
Length inMeters (m)
Resistance inOhms (Ω)
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ALR ρ
=ρ : resistivity
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iRv =R
G 1=Gvi = G : conductance
R : resistance
Ohm’s law
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What is an Insulator?
• A material that does not allow electrons to flow freely• Examples:
– Wood– Plastics– Ceramics– Amber
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What is a conductor?
• A material that allows free electron movement• Examples:
– Aluminum– Gold– Copper– Most Metals
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What is a semiconductor?
• A class of materials whose electron conductivity is between that of a conductor and insulator
• Examples:– Silicon– Germanium
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Summary
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> 1021
1 × 1012
1 × 1019
10-8 to 1
2.73 × 10-8
3.5 × 10-5
1.72 × 10-8
2.27 × 10-8
1.12 × 10-6
1.63 × 10-8
5.44 × 10-8
Fused quartzGlass (typical)Teflon
Insulators
Silicon (divice grade)depends on impurity concentration
Semiconductors
AluminumCarbon (amorphous)CopperGoldNichromeSilverTungsten
Conductors Resistivity
Resistivity for Various Material at 300K
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Mechanical Strain Gauge(Resistor)
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Resistor Color Codes
-2 Silver-1 Gold 0 Black1 Brown2 Red3 Orange4 Yellow5 Green6 Blue7 Violet8 Gray9 White
Tolerance 5% Gold10% Silver20% No 4th band
f
p
n
μ
m
k
M
G
Abbreviation
10-15
10-12
10-9
10-6
10-3
103
106
109
Scale factor
femto-
pico-
nano-
micro-
milli-
kilo-
meg- or mega-
giga-
Prefix
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INTRODUCTION TO CIRCUITS
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Kirchoff Current Law : Σ Ik=0“The sum of current at a node is always zero”Parallel Circuit : Constant Voltage
∑∑ ===k kk k Z
ZZV
ZVI 1
Kirchoff Law
Resistor ∑=k
kRR /1 Capacitor ∑=k
kCC
Kirchoff Voltage Law : Σ Vk=0“The sum of voltage drop around a loop is always zero”
Serial Circuit : Constant Current
∑∑ ===k
kk
k ZZIZIZV
Resistor ∑=k
kRR Capacitor ∑=k
kCC /1
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Concept Questions
• How can you change the resistance of a resistor?
• How would you determine the resistivity of pencil lead?
• How would you determine the Number of Electrons in Earth?