• Electricity – From the word “Elektron”– Greek for “amber”
Electrical systems have two main objectives:
• To gather, store, process, transportinformation & Energy
• To distribute and convert energy
Electrical Engineering Subdivisions
Communication Computer Systems Control Systems Electromagnetics
Electronics Power Systems Signal Processing
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?
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
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 ===
Circuit Symbols• Battery or Power Supply• Resistor• Capacitor• Switch
More Circuit Symbols
• DC Voltage Supply• AC Voltage Supply• Open Circuit• Closed Circuit• Short Circuit • DC Current Supply• AC Current Supply
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
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
Current Equation
tqi∆∆
=
Current in Amperes (A)
Charge inCoulombs (C)
Time in Seconds (s)
dt)t(dqi =Calculus:
Figure 1.4
dttdqti )()( = (1.1)
∫ +=t
ttqdttitq
0
)()()( 0(1.2)
)(tq : Charge
)(ti : Currentt0 : some initial time
at which the chargeis known
Types of Electricity
• Static Electricity - no motion of free charges• Current Electricity - motion of free charges
– Direct Current (DC)– Alternating Current (AC)
Voltage Description
Current Description
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
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
ia = 4A ib = -2A ic = -8A
ia = ib = ic
Examples of KCL
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
baab vv −=
KIRCHHOFF’S VOLTAGE LAW(KVL)
The algebraic sum of the voltages equals zero for any closed path (loop) in an electrical circuit.
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
A, B C D, E, F
Parallel
Serial
Rearrangement of Circuit
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
POWER AND ENERGY
)()()( titvtp =
vip =
2Rip =
Rvp
2
=
∫=1
2
)(t
tdttpw
Power
Energy
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
Independent Source
Voltage or Current is specified by itself into Circuit.
Constant Voltage Source Constant Current Source
Battery, Home Power Specially Designed Circuit
Dependent Voltage Source
Voltage or Current is determined by others in Circuits
Τransistor, Amplifier, Electrical Generator
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
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)
ALR ρ
=ρ : resistivity
iRv =R
G 1=Gvi = G : conductance
R : resistance
Ohm’s law
What is an Insulator?
• A material that does not allow electrons to flow freely• Examples:
– Wood– Plastics– Ceramics– Amber
What is a conductor?
• A material that allows free electron movement• Examples:
– Aluminum– Gold– Copper– Most Metals
What is a semiconductor?
• A class of materials whose electron conductivity is between that of a conductor and insulator
• Examples:– Silicon– Germanium
Summary
> 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
Mechanical Strain Gauge(Resistor)
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
INTRODUCTION TO CIRCUITS
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
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?