Transcript Chapter 1

BENG1113
PRINCIPLE OF ELECTRICAL AND ELECTRONICS
Chapter 1 (week 1)
FACULTY OF ELECTRONIC AND
COMPUTER ENGINEERING
Learning Outcome
• Upon completion of this chapter, student
should be able to:
–
–
–
–
–
Describe the basic structure of atoms
Define nucleus, proton, neutron and electron
Describe ionization and free electron
Define conductor, semiconductor and insulator
Convert decimal no to standard or engineering
notation
Chapter 1: Introduction to Electricity
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Chapter 1
•
Subtopics:
1.
2.
3.
4.
5.
6.
7.
8.
Atomic structure
SI units, Scientific and Engineering notation
Electrical charges
Electrical quantities - voltage, current and resistance
Active and passive components
Basic electrical instruments
Basic circuit measurement
Electrical safety.
Chapter 1: Introduction to Electricity
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Atomic Structure
• ATOM : The smallest particle of an
element that possesses the unique
characteristics of that element.
• PROTON : The basic particle of
positive charge.
• ELECTRON : The basic particle of
negative charge.
• NEUTRON : An uncharged particle
found in the nucleus of an atom.
• NUCLEUS : The central part of an
atom containing protons and
neutrons.
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Balanced Atom
• an equal number of electrons and protons.
• no electrical charge.
Chapter 1: Introduction to Electricity
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Valance Electrons
• VALANCE SHELL : The
outermost shell of an atom.
• VALANCE ELECTRONS :
Electrons in the valance shell.
• The valance electrons
contribute to chemical
reactions and bonding within
the structure of a material
and determine its electrical
properties.
Ionization
• Since electrons are lighter
than protons and are outside
the nucleus, they can be easily
moved from atom to atom to
form electrons
• When an atom absorbs
energy, the valance electrons
possess more energy and they
can actually escape from the
outer shell and becoming free
electrons.
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The periodic table
Exercises
1. How many electrons contains in the
valence shell for the elements below.
a) Sodium
b) Chlorine
2. Draw the atomic structure of the copper
atom (no.of electrons = 29).
Chapter 1: Introduction to Electricity
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CONDUCTORS
• A material that easily conduct electrical
current.
• A CONDUCTOR has 1 to 3 valence
electrons in the outermost shell. Therefore
its electrons tend to move to other atom.
• Most metals are good conductors and the
best conductors are single-element
materials such as copper, silver, gold
and aluminium.
INSULATORS
• A material that does not conduct electrical
current under normal conditions.
• Most good insulators are compounds
rather than single-element material such
as rubber, plastics, glass, mica, and
quartz.
• An insulator is any material with 5 to 8
valence electrons in the outer ring.
SEMICONDUCTORS
• A material that is between conductors and
insulators in its ability to conduct electrical
current. It has exactly 4 valence electrons.
• A semiconductor in its pure (intrinsic) state is
neither a good nor a good insulator.
• The most common single-element
semiconductors are silicon, germanium, and
carbon.
• The most common compound semiconductor is
gallium arsenide.
SI units [1]
Quantity
Unit
length
mass
time
electric current
meter
kilogram
second
ampere
Kelvin
candela
mole
temperature
luminous intensity
amount of substance
Symbol
m
kg
s
A
K
cd
mol
Table 1-1
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• This is the units that are derived from the
fundamental units except for current since
it is a fundamental unit
Quantity
Table 1-2
current
Symbol
A
ampere
charge
coulomb
C
voltage
volt
V
resistance
ohm
power
W
watt
Chapter 1: Introduction to Electricity
Unit
W
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• All magnetic units are derived from the
fundamental units [1].
Table 1-3
Quantity
flux density
magnetic flux
magnetizing force
magnetomotive force
permeability
reluctance
Unit
Symbol
tesla
weber
ampere-turns/meter
ampere-turn
webers/ampere-turns-meter
ampere-turns/weber
T
Wb
At/m
At
Wb/Atm
At/Wb
Chapter 1: Introduction to Electricity
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Scientific notation
• Provides a convenient method for
expressing large and small numbers
1=100
10 =101
100 =102
1000 =103
Chapter 1: Introduction to Electricity
1/10 =0.1 =10-1
1/100 =0.01 =10-2
1/1000 = 0.001 =10-3
1/10,000 =0.0001 =10-4
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Mathematical Operation
•
To perform addition or subtraction using
powers of ten, the power of ten must be the
same for each term:
A 10n  B 10n  ( A  B) 10n
•
Multiplication
•
Division A 10n A
nm


10
B 10m B
Power ( A 10n )m  Am 10nm
•
( A 10n )( B 10m )  ( A)( B) 10n m
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Exercises
1. Express each number in scientific
notation
a)
b)
c)
d)
e)
200
5000
85000
3,000,000
4750
Chapter 1: Introduction to Electricity
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2. Express each of the following numbers in
scientific notation:
a)
b)
c)
d)
0.2
0.005
0.00063
0.000015
3. Express each number as a regular
decimal number:
a)
b)
c)
d)
1 x 105
2 x 103
3.2 x 10-2
2.5 x 10-6
Chapter 1: Introduction to Electricity
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Engineering notation
• Similar to scientific notation
• A number can have from one to three digits to
the left of the decimal point and the power-often exponent must be a multiple of three [1]
• For example;
33000 = 3.3 x 104 = 33 x 103
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• Matrix prefix
– Specific powers of ten in engineering notation
have been assigned prefixes and symbols [2]
m
milli
10-3
P
peta
1015
m
micro
10-6
T
tera
1012
n
nano
10-9
G
giga
109
p
pico
10-12
M
mega
106
f
femto
10-15
k
kilo
103
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• Metric unit conversions
– Larger unit: move the decimal point to the
right
– Smaller unit: move the decimal point to the
left
– e.g.
0.15mA = 150µA
Chapter 1: Introduction to Electricity
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Exercises
1. Perform the mathematical operation;
a)
b)
c)
d)
e)
f)
g)
h)
6300 + 75000
0.0096 – 0.000086
(0.0002)(0.000007)
(340,000)(0.00061)
0.00047/0.002
690000/0.0000013
(0.00003)3
(90800000)2
Chapter 1: Introduction to Electricity
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2. Example 1-8 [1]: express the following
numbers in engineering notation
a)
b)
c)
d)
e)
f)
82,000
243,000
1,956,000
0.0022
0.000000047
0.00033
3. Example 1-10 [2]: Convert the following
• 20 kHz to megahertz
• 0.01ms to microseconds
• 0.002km to millimeters
Chapter 1: Introduction to Electricity
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Electrical Charges
• Charges of opposite signs (one negative and
one positive) attract one another.
• Charges of the same sign (both positive and
both negative) repulse one another.
Chapter 1: Introduction to Electricity
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Electrical Charges
• The unit of charge [1]:
– The unit of charge is denoted by Coulomb
– One coulomb is the total charge possessed
by: 6.25 x 1018 electrons or protons
– A single electron has a charge of 1.6 x 10-19
C and a single proton has a charge of +1.6 ×
10-19 C.
– Total charge;
number of electrons
Q
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6.25 10 electrons/C
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Exercises
1. How many Coulombs of charge do 93.8 x
1016 electron represent?
2. How many electrons does it take to have
3C of charge?
Chapter 1: Introduction to Electricity
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Electrical Force
• Electrical forces act between charges
kQ1Q2
Felectrical 
D
• Q1 and Q2 = charge on the objects (in C)
• D = distance between objects (in meters)
• k = a constant = 8.99 x 109 N m2/coul2
• The strength of the electrical force
decreases as the distance between the
charged objects increases
Basic Electrical Components and
Instuments
• Resistors
• Resistors resist, or limits, electrical current in a circuit.
• Capacitors
• Capasitors store electrical charge; they are used to
block direct current (dc) and pass alternating current
(ac).
• Inductors
• Inductors, also known as coils, are used to store
energy in an electromagnetic field; they serve many
useful functions in an electrical circuit
• Transformers
• Transformers are used to magnetically couple ac voltages from one
point in a circuit to another, or to increase or decrease the ac
voltage. Companies such as TNB use huge transformers to change
voltages for high-voltage transmission lines.
• Electronic Instruments
• There are four basic electronic instruments normally found in
laboratory and will be use throughout the lab session for this course.
These instruments include:
•
• DC power supply - provide current and voltage to power electronic
circuits.
• Function generator – provide electronic signals.
• Multimeter – with its voltmeter, ammeter and ohmmeter functions for
measuring voltage, current and resistance, respectively
• Oscilloscope – observe and measure ac voltages.
Voltage
• Voltage is the electrical force that moves
electrons through a conductor. The
pressure also known as EMF (Electro
Motive Force) that pushes electrons.
• Voltage is expressed as;
W
V
Q
• V = voltage in volts (V)
• W = energy in joules (J)
• Q = charge in coulombs (C)
• One volt is the potential difference
(voltage) between two points when one
joule of energy is used to move one
coulomb of charge from one point to the
other.
Exercises
• Determine the voltage
• 10J / 1C
• 5J / 2C
• 100J / 25C
• If 50J of energy are available for every
10C of charge, what is the voltage?
• 500J of energy are used to move 100C of
charge through a resistor. What is the
voltage across the resistor?
Voltage Source
• Battery: A battery is a type of voltage source that
convert chemical energy into electrical energy. A battery
consists of one or more electrochemical cells that are
electrically connected.
• four basic components: a positive electrode, a negative
electrode, electrolyte and a porous separator.
-
+
Porous separator
Electrolyte
Negative electrode
Positive electrode
• Solar cells: The operation of solar cells is based on
the photovoltaic effect (light energy is converted directly
into electrical energy). It has 2 layers of different types of
semiconductive materials joined together to form a
junction. When one layer is exposed to light, many
electrons acquire enough energy to break away from
their parent atoms and cross the junction, and thus a
voltage is developed.
• Generator:
Electrical generators convert
mechanical energy into electrical energy using a
principle called electromagnetic induction. A conductor
rotated through a magnetic field, and a voltage is
produced across the conductor.
• Electronic power supply: Electronic power
supply does not produce electrical energy from some
other from energy. They simply convert the ac voltage
from wall outlet to a constant (dc) voltage.
• Measuring instrument: A VOLTMETER
Current
• Current is the movement or flow of charge
(electrons) from the negative end of the
conductor to the positive end
• Current in a conductor material is measured by
the number of electrons (amount of charge) that
flow past a point in a unit of time
Q
I
t
I = current in Ampere (A)
Q = charge of the electrons in coulombs (C)
t = time in seconds (s)
• One ampere (1A) is the amount of current that exists
when a number of electrons having a total charge (1C)
move through a given cross-sectional area in one
second.
• Electricity with electrons flowing in only one direction is
called Direct Current (DC). It flows in one direction,
positive to negative, steadily. A graph of a DC voltage or
current would look like a flat horizontal line.
• Electricity with electrons flowing back and forth, negative
- positive- negative, is called Alternating Current, or AC.
It literally changes direction at a certain rate, called its
frequency, measured in Hertz.
• Ordinary household electricity in Malaysia is 240 VAC,
50 Hz. A graph of 240 VAC is a sine wave. AC can be
used at it is in light bulbs and motors, but for electronic
devices, it must be stepped down to a lower voltage and
then converted to DC. For example, the CPU in many
computers typically takes 3.6 volts DC.
• Measuring instrument: Ammeter
Exercises
• 10C of charge flow past a given point in a
wire in 2s. What is the current in amperes?
• If there are 8A of direct current through the
filament of a light bulb, how many
coulombs have moved through the
fillament in 1.5s?
Resistance
• Resistance, R, is the force that reduces or stops
the flow of electrons.
• Opposite to current and measured in Ohms (W)
• The schematic symbol is shown below
• Conductance, G, is the reciprocal of resistance.
• The unit is in Siemens (S)G  1
R
• Measuring instrument: Ohmmeter
Resistor Colour Codes
Color
Resistance value, first three bands:
First band 1st digit
Second band 2nd digit
*Third band multiplier (number of
zeros following the 2nd digit)
Fourth band tolerance
Digit
Multiplier Tolerance
Black
0
10 0
Brown
1
10 1
1% (five band)
Red
2
10 2
2% (five band)
Orange
3
10 3
Yellow
4
10 4
Green
5
10 5
Blue
6
10 6
Violet
7
10 7
Gray
8
10 8
White
9
10 9
Gold
5%
10 -1
5% (four band)
Silver
 10%
10 -2
10% (four band)
No band
 20%
* For resistance values less than 10W, the third band is either gold or silver. Gold is for a multiplier of 0.1 and silver is for
a multiplier of 0.01.
• What is the resistance and the tolerance?
Alphanumeric Labeling
• Two or three digits, and one of the letters R, K,
or M are used to identify a resistance value.
• The letter is used to indicate the multiplier, and
its position is used to indicate decimal point
position.
Power
• When current is forced through a resistance,
work is said have been done. Power is the rate
of working, represented by "P". Energy is the
capacity to do work.
• Power is energy per time or the rate of working,
represented by "P". The standard unit used in
electricity is the Watt (W) = 1 Joule / second.
• The amount of power consumed by an electrical
device is the rate at which it dissipates energy.
2
V
P  IV  I R 
R
2
Basic Circuit Measurement
• Multimeter
Digital Multimeters (DMM)
Analog Multimeter
• Meter symbols
Measuring Current
• Most analog ammeters have a number of
possible settings for the maximum possible
current that can be measured; for example: 2 A,
200 mA, 20 mA, 2 mA. You should always start
by turning the setting to the highest possible
rating (for example, 2 A). If the ammeter reading
is too small from the selected scale, then you
can reduce the scale to get the reading. It is
important not to overshoot the maximum value
that can be read.
• For example, if the current is about 75 mA, then
the ammeter would be set to the 200 mA scale
for the most accurate reading. Setting to the
20 mA scale would overload the ammeter and
most likely open its internal fuse.
Measuring Voltage
Measuring Resistance
Measured Numbers
• Error : The difference between the true value
and the measured value
• Accuracy : The degree to which a measured
value represents the true or accepted value of a
quantity. A measurement is said to be accurate if
the error is small.
• Precision : The repeatability or consistency of a
measurement
• Resolution
– The smallest increment of quantity that the
meter can measure. The smaller the
increment, the better the resolution.
0.01V
0.001V
Chapter 1: Introduction
to Electricity
53
Passive Components
• Passive components:
Components that do
not supply voltage or
current
Color bands
Resistance material
(carbon composition)
Insulation coating
Leads
– Examples
•
•
•
•
Resistors
Capacitors
Inductor
Transformer
Foil
Mica
Foil
Mica
Foil
Mica
Foil
Mica capacitor_
Tantalum electrolytic
capacitor (polarized)
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Active Components
• The components that have their own
power source.
• Passive components are used in
conjunction with active components to
form an electronic system
– Voltage and current sources
• Battery, Generator, Fuel cell
• Transistor
• Integrated Circuit (IC)
Electrical Safety
• Electrical shock :when voltage is applied across two
points on human body , it caused current to flow through
the body
• The severity of the resulting electrical shock depends on
the amount of voltage and the path that the current takes
through the body
• Effects of current on the human body:
– Depends on voltage and body resistance.
• Body resistance:
– Typically between 10kΩ and 50kΩ
– The moisture of the skin and body mass also affects
the resistance between two points
Chapter 1:
Electrical Safety
• Some of safety precautions :
– Avoid contact with any voltage source. Turn off
power before you work on circuits when touching
circuit parts is required.
– Do not work alone. A telephone should be available
for emergencies.
– Remove rings, watches, and other metallic jewelry
when you work on circuits.
– Always wear shoes and keep them dry
– Do not stand on metal or wet floor
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