Transcript Chapter 1

BENE 1113
PRINCIPLES OF ELECTRICAL
AND ELECTRONICS
CHAPTER 1
“INTRODUCTION
ELECTRICITY”
OF
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The meaning of the subject title
• Principles – a comprehensive and fundamental
•
•
law, a rule of conduct
Electrical – is a field of engineering that deals
with the study and application of electricity,
electronics and electromagnetism
Electronics - is the study of the flow of charge
through various materials and devices such as
semiconductors, resistors, inductors, capacitors,
nano-structures and vacuum tubes.
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Electrical versus Electronic
• Electrical engineering may or may not
encompass electronic engineering. Where a
distinction is made, electrical engineering is
considered to deal with the problems associated
with large-scale electrical systems such as power
transmission and motor control, whereas
electronic engineering deals with the study of
small-scale electronic systems including
computers and integrated circuits
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Learning outcome of this topic
• At the end of the topic, the students
should be able to explain the basic
concept of electrical and electronics.
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TOPICS COVERED:
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Introduction of electricity
Static and dynamic electricity
Electric current and electric charge
Electrical base units
Electric field
Electric flux
Electrostatic
Coulomb’s law
Ampere’s law
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1.1 INTRODUCTION OF
ELECTRICITY
The importance study of electricity:
• It is hard to imagine the world without electricity, it
touches and influences our daily lives in hundreds of
ways.
• Without electricity, most of the things we use and enjoy
today would not be possible.
• Study of electricity will be based upon the electron
theory, which assumes that all electrical and electronic
effects are due to the movement of electrons from place
to place.
• Electricity is the flow of electrons through simple
materials and devices.
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1.1.1 Review of Electricity
• Molecule: the combination of the two or more atoms.
• Atom: the smallest particle into which an element
can de divided.
• Nucleus: the positively charged central part of atom.
• Neutron: the neutral particles in the nucleus that
behave a combination of proton and
electron.
• Proton: the positively charged particles in the
nucleus.
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• Electron: the very small negatively charged particles
which are circle the nucleus in orbits.
• Free electrons: electrons that have left their orbit in
an atom and are wandering freely through a material.
• Electric current: the movement of free electrons.
• Positive charge: A deficiency of electrons.
• Negative charge: A surplus of electrons.
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1.2 STATIC AND DYNAMIC
ELECTRICITY
• You walk across the carpet, reach for the door knob
and..........ZAP!!! You get a shock.
• Or, pull off your hat and......BOING!!! All your hair stands
on end. What is going on here?
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Answer:
Static Electricity
• If you walk across a carpet, electrons move from the
rug to you. Now you have extra electrons. Touch a
door knob and ZAP! The electrons move from you to
the knob. You get a shock.
• When you pull your hat off, it rubs against your hair.
Electrons move from your hair to the hat. Now each
of the hairs has the same positive charge.
the hairs try to move away from each other.
The furthest they can get is to stand up and
away from all the other hairs.
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• Static electricity is the situation where electrical charges
build up on the surface of a material.
• It is called “static” because there is no current flowing as
in AC or DC electricity.
• Static electricity is usually caused when materials are
rubbed together. The result is that objects may be
attracted to each other or may even cause a spark to
jump from one object to the other.
• Common examples of static electricity in action of
flyaway hair and the sparks that can occur when you
touch something.
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Dynamic Electricity
• When two bodies are at different potentials, an electric
force exists between them.
• This force can cause an electron flow between the
bodies if a conducting path exist between them.
• The electric force is termed an electromotive force
(e.m.f), it is measured by the potential difference in Volts
between two points.
• If points of different potential are joined by an electrical
conductor, the electrons will be forced from the point
where there is a surplus of electrons to a point where
there is a deficiency.
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• Electrons will flow from a point of higher electron
potential to one of lower electron potential whenever a
conducting path exists between those points.
• The rate of flow of electricity is governed by the two
factors; potential difference and electrical material.
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Unit of Charge
• The charge on an electron is so small that it is not
convenient to select it as the unit of charge.
• In practice, Coulomb is used as the unit of charge.
• 1 C of charge is equal to the charge on 6.25x1018
electrons.
1 Coulomb=charge on 6.25x1018 electrons/protons
-Q : 6.25x1018 (more electron than proton)
+Q : 6.25x1018 (more proton than electron)
Charge proton, e: 1.602 x 10 -19 C
Charge electron, -e: 1.602 x 10 -19 C
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– Total charge;
number of electrons
Q
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6.25 10 electrons/C
• 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?
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1.3 ELECTRIC CURRENT AND
ELECTRIC CHARGE
• All atoms are bound together by forces of attraction
between nucleus and its electrons.
• Electrons in the outer orbits of an atom, however are
attracted to their nucleus less powerfully that are
electrons whose orbits are nearer the nucleus.
• In certain material( electrical conductor), these outer
electrons are so weakly bound to their nucleus that they
can easily be forced away from it altogether and left to
other atoms at random.
• Such electrons are called free electrons. It is directional
movement of free electrons which makes an electric
current.
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• Electrons which have been forced out of their orbits
create a deficiency of electrons in the atoms they leave
and will cause a surplus of electrons at the point where
they come to rest.
• A material with a deficiency of electrons is positively
charged; one possessing a surplus of electrons is
negatively charged.
• When these charges exist and not in motion, it is called a
static electricity.
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• Static electricity usually involves nonconductors. But if
the materials were conductors, then the free electrons
easily flow back toward the positive charges and the
material would be neutral or uncharged.
• Like charge (both positive or both negative) will repeal
each other while unlike charge (1 positive and 1
negative) will attract each other.
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1.4 ELECTRICAL BASE UNITS
1. Coulomb
– The unit of charge is Coulomb (C), where 1C is 1
Ampere second.
– The Coulomb can be defined as the quantity of
electricity which flows past a given in an electric
circuit when a current of 1 Ampere is maintained for
1 second.
– Thus,
Q=It
where Q: magnitude of charge
I: current
t: time
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– Exercises:
• What is the current if 2 C passes a point in 5 s?
• Then coulombs of charge flow past a given point in
a wire in 2 s. What is the current in amperes?
• The charge flowing through a wire is 0.16 C every
64 ms. Determine the current in amperes.
• Determine how long it will take 4 x 1016 electrons
to pass through wire if the current is 5 mA.
Answers
0.4 A
5A
2.50A
1.28s
2. Electrical potential and e.m.f (Voltage)
– The unit of electric potential and e.m.f are volt(V),
where 1 volt is 1 joule per coulomb.
– 1 volt can be defined as the difference in potential
between two points in a conductor which, when
carrying a current of 1 ampere, dissipates a power
of 1 watt.
Q= I t
– Thus,
watt
joule / sec ond

ampere
ampere
joule

coulomb
Volt 
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– Exercises:
a) If 50J of energy are available for every 10 C of
charge, what is the voltage?
b) Find the voltage between two points if 60J of
energy are required to move a charge of 20 C
between the two points.
c) Determine the energy expended when moving a
charge of 50 µC between two points if the
voltage between the points is 6V.
Answers
a) 5V
b) 3V
c) 300µJ
3. Resistance
– The unit of resistance is ohm where 1 ohm is 1 volt
per ampere.
– It can be defined as the resistance between two
points in a conductor when a constant electric
potential of 1 volt applied at the points produces a
current flow of 1 ampere in the conductor.
– Thus,
R= V/I
where;
V: potential difference across two points
I: current flowing between the two points
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– the schematic symbol is shown below
– Conductance is the reciprocal of resistance.
– The unit is in Siemens (S)
1
G
R
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
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1.5 ELECTRIC FIELD
• Like charge will repeal each other while unlike charge
will attract each other.
• There is a field of force that surrounds the charges and
the effect of attraction or repulsion is due to the field.
• This field or force is called an electric field of force. It is
also sometimes called an electrostatic field or a dielectric
field since it can exist in air, glass, paper, vacuum or in
any other dielectric or insulating material.
• The space or field in which a charge experiences a force
is called an electric field or electrostatic field.
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Electric field lines have the following properties:
• They start on a positive charge and end on a
negative charge.
• They never cross.
• They are closer together in regions where the field is
stronger and further apart where the field is weak.
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1.6 ELECTRIC FLUX
• The total electric lines of force which flow outward
from a positive charge is called electric flux.
• Electric flux is a measure of the overall size of electric
field and it is measured in Coulomb, C.
• The symbol for electric flux is psi,Ψ.
• The electric flux density at any section in an electric
field is the electric flux crossing normally per unit area
of that section:

Electric flux density , D 
C / m2
A
where,  : electric flux in Coulomb
A : area in m 2
• Electric flux density is a vector quantity: possessing
both magnitude and direction.
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1.7 ELECTROSTATIC
• Another situation where charges do not move but remain
static or stationary on the bodies, such a situation will
arise when the charged bodies are separated by some
insulating medium, disallowing the movement of
electrons.
• This is called static electricity and the branch of
engineering which deals with static electricity is called
electrostatics.
• The most useful outcomes of static electricity are the
development of lightning rod and the capacitor.
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1.8 COULOMB’S LAW
• First law: related to the nature of force between two
charged bodies.
“like charges repel each other while unlike charges
attract each other”
• Second law: tell about the magnitude of force between
two charged bodies.
“The force between two charges is proportional to
the product of the charges and inversely
proportional to the square of the distance between
them.”
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Mathematically;
where;
F: force in Newtons
Qa, Qb: charge in Coulomb
r: distance in meter
k: constant( the value depends upon medium
in which the charges are placed and the
system of units employed)
k is given by;
where;
ε0 : absolute permittivity of vacuum or air
εr: relative permittivity of the medium in
which the charges are placed
ε0: 8.85x10-12 F/m
εr: the value is different for different media
(for vacuum or air= 1)
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Example:
Two small conducting spheres A
and B having charges of -2.5 x 106 C and -2.5 x 10-6 C respectively
are allowed to touch one another
briefly. After touching, they
separate until the force between
them is 0.2 N. What is the distance
between two charges?
(Coulomb's constant, k: 9.0 x 109 N.m2.C-2.)
Solution:
r = 53 cm
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1.9 ELECTRIC POTENTIAL
• When a body is charged, work is done by charging it.
The work done is stored in the body in the form of
potential energy.
• The charged body has the capacity to do work by
moving other charge either by attraction or repulsion.
• The ability or capacity of the charged body to do work
is called electric potential.
• The greater the capacity of a charged body to do work,
the greater is its electric potential.
Electric potential,V 
work done
ch arg e
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• The work done is measured in joule and charge in
Coulomb, therefore the unit of electric potential will be
joule/coulomb or Volt.
• A body is said to have an electric potential of 1 Volt if 1
joule of work is done to give it a charge of 1 Coulomb.
• We can say that a body has an electric potential of
5Volt, it means that 5 joule of work has been done to
charge the body to 1 Coulomb.
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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?
1.10 POTENTIAL DIFFERENCE
• If two bodies have different electric potentials, a potential
difference exist between the bodies.
• The difference in the potentials of two charged bodies is
called potential difference.
A
+5V
B
+3V
(i)
A
B
(ii)
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1.9.1 CONCEPT of e.m.f and POTENTIAL
DIFFERENCE
• The e.m.f of a device (battery), is a measure of the
energy the battery gives to each coulomb of charge.
• Thus, if a battery supplies 4 joules of energy per
coulomb, we say that it has an e.m.f of 4 Volts.
• The potential difference between two points, say A
and B, is the measure of energy used by 1 coulomb
charge in moving from A to B.
• Thus, if potential difference between A and B is 2 Volts,
it means that each coulomb will give energy of 2 joule in
moving from A to B.
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1.10 AMPERE’S LAW
Ampere’s Law states that:
“for any closed loop path, the sum of the length
elements times the magnetic field in the direction
of the length element is equal to the permeability
times the electric current enclosed in the loop”
 B  l  o I
where;
B : magnetic flux density
l : length of conductor
 o : permeabili ty
I : current
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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
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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)
THANK
YOU
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