Transcript - Muhazam

EEE1012
Introduction to Electrical &
Electronics Engineering
Chapter 1: Fundamental Laws of Electricity
by Muhazam Mustapha, July 2010
Learning Outcome
• By the end of this chapter, students are
expected to understand the most basic
laws of electricity, i.e. Ohm’s and
Kirchhoff’s Law, the units involved and the
related symbols
• The ONLY way to score in this course is to
do a lot of exercises
Chapter Content
•
•
•
•
•
Brief history of electricity
Units and Symbols
Ohm’s Law
Kirchhoff’s Law
Resistance and source combination, and
voltage and current division
• Analysis of single loop and single nodepair circuit
Brief History of Electricity
Source of Electricity
• Electricity is the direct phenomena
due to the net displacement of the
sub-atomic particle: ELECTRON
• If the displaced electron is freely
moving: ELECTRODYNAMIC
phenomenon
• If the displaced electron is tied-up
into material: ELECTROSTATIC
phenomenon
• What we want to learn in this course
is electrodynamic phenomenon
Source of Electricity
• Electron displacement can be achieved by:
–
–
–
–
Chemical reaction (batteries)
Mechanical interaction (electrostatic)
Magnetic influence (generator)
Nuclear reaction (atomic batteries)
• Physical connection that gives a net electron
movement in one close loop is called circuit
• Circuits consist of: POWER supply and LOAD
Discoveries of Electricity
• The earliest known use of electricity was by the
Mesopotamians: BAGHDAD BATTERY
[http://en.wikipedia.org/wiki/Baghdad_Battery]
• The original connection between lightning and
electricity was made by the Muslim Arabian
scientists [http://en.wikipedia.org/wiki/Electricity]
– But the first recorded experiment was made by
Benjamin Franklin
• The connection between mechanical
movement, magnetic field and electricity was
made by Michael Faraday
Units and Symbols
Electrical Units
• Electric charge: Coulomb, C
– Amount of electric charge in material
• Electric current: Ampere, A [C/s]
– Rate of charge movement per second
• Voltage: Volt, V [J/C]
– Electrical tension (potential) created when 1 C of
charge is displaced using 1 Joule of energy
• Electric power: Watt, W [VA]
– Dissipated power when 1 A of current flows with 1 V
of electrical potential
Electrical Units
• Resistance: Ohm, Ω [V/A]
– Opposition to electric flow in material when 1 A is
flowing with 1 V of electrical potential
Ω
• Conductance: Siemens, σ or Mho,
– Reciprocal of resistance
• Capacitance: Farad, F
– Capacitor that can sustain 1 C of charge when 1 V of
potential is given
• Inductance: Henry, H
– Inductor that can sustain 1 Wb[*] of magnetic flux
when 1 A current is flowing
Circuit Symbols
Resistor
Current
Supply
Load
Capacitor
Voltage
Supply
Inductor
Ohm’s and Kirchhoff’s Law
Ohm’s Law
• Electrical Law relating Current, Potential and
Resistance
V = IR
Kirchhoff’s Voltage Law
• In closed loop circuit, the total voltage supply is
equal to the total voltage drop
V2
V3
V1 + V2 + V3
= V4 + V5 + V6
V1
V4
V6
V5
Kirchhoff’s Current Law
• At a circuit junction (node), the total incoming
current is equal to the total out-going current
I1 + I2 + I5
= V3 + V4
I3
I2
I4
I1
I5
Circuit Simplification
Component in Series
• Components are connected head-to-tail
• Series current supplies are not legal
arrangement without considering internal
conductance, unless they are the same values
• Voltage supplies are combined by summing up
V1
VT
V2
V3
VT = V1 + V2 + V3
Components in Series
• Voltage drops ratio across resistors are equal to
the resistance ratio
• Currents are the same through all components
• Resistors are combined by summing up
RT
R1
I1
R2
I2
V1
R3
I3
V2
VT
V3
V1 R 1 V2 R 2 V3 R 3

,

,

VT R T VT R T VT R T
I1  I 2  I3
R T  R1  R 2  R 3
Components in Parallel
• Components are connected head-to-head, tailto-tail
• Parallel voltage supplies are not legal
arrangement without considering internal
resistance, unless they are the same values
• Current supplies are combined by summing up
IT
I1
I2
I3
IT = I1 + I2 + I3
Components in Parallel
• Current ratio through resistors are equal to the
conductance ratio
• Voltage are the same across all components
• Resistors are combined by combining
conductance
I1 G1 I 2 G 2 I3 G 3

, 
, 
IT G T IT G T IT G T
IT
RT
I1
I2
V1
R1 V2
I3
R2 V3
V1  V2  V3
R3
1
1
1
1



R T R1 R 2 R 3
Bridge Circuit
• Couldn’t be resolved to series or parallel
• Analysis can be done as mesh or nodal analysis
(Chapter 2)
Exercise
Calculate all V, I and R for all resistors:
1Ω
10V
2Ω
6Ω
1Ω
1Ω
4Ω
2Ω
2Ω
1Ω
Some Special Notations
Ground & Power
• Power can just be shown as a bubble at the top
– This simplifies the circuit and shows voltage more
clearly
• Ground is a COMMON point whose voltage is
assumed to be at a reference point 0V
20V
POWER
20V
same point
GROUND (0V)
Relative Potentials
Va
Vab
Vb
• Voltages with single
subscripts are relative to
ground
• Voltages with double
subscripts are of the first
subscript as seen from the
second:
Vab = Va − Vb
Parallel Operator
R1
RT = R1 R2
R2
=
R1R2
R1 + R2