Transcript chapter 1 – electronic principles - ja505

Topic 1
ELECTRONIC PRINCIPLES
1.1Basic Electronic Principles
LECTURER NAME: MR. KHAIRUL AKMAL BIN NUSI
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Subatomic
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• An atom is the basic component
of a chemical element, but
atoms themselves are composed
of various combinations of
smaller, or subatomic, particles,
such as electrons, protons, and
neutrons.
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Nucleus
• At the center of every atom
is a nucleus, comprised of a
number of protons and (with
the exception of hydrogen)
neutrons. The simplest and
lightest chemical element is
hydrogen, which has a
nucleus containing just one
proton and no neutrons. Each
distinct chemical element has
a unique number of protons,
coupled with a number of
neutrons, which can vary.
Protons
• A proton is
a subatomic particle with a
positive charge equivalent to
the negative electrical charge
of an electron. Protons and
neutrons together form the
nucleus of an atom. The
number of protons in a nucleus
determine the 'atomic
number' of the element – the
atomic number of hydrogen is
1; carbon has 6 protons so its
atomic number is 6; iron has
26 protons, so its atomic
number is 26, and so on.
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Neutrons
• A neutron
is subatomic particle similar
in mass to a proton, with no
electrical charge. The
number of neutrons in a
nucleus determines the
isotope, or particular form,
of the element. For
instance, iodine 127 and
iodine 131 are both forms of
iodine, with the same atomic
number and the same
number of protons, but with
different numbers of
neutrons and therefore
different atomic weights.
Electrons
• An electron is
a subatomic particle with a
negative electrical charge.
Electrons orbit around and exist
outside of the nucleus of an
atom. They are bound to the
atom by electromagnetic forces,
but they are very light and can
move between atoms creating an
electrical current. All electrical
and electronic activity is created
by moving electrons. As they
form the outer shell or shells of
an atom, electrons are largely
responsible for how chemicals
interact with each other.
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1a) Charged particles in matter :Atoms have three types of sub atomic particles. They are
electrons, protons and neutrons.
Electrons are negatively charged (e-), protons are positively
charged (p+) and neutrons have no charge (n).
The mass of an electron is 1/2000 the mass of a hydrogen
atom. The mass of a proton is equal to the mass of a hydrogen atom
and is taken as 1 unit. The mass of a neutron is equal to the mass of
a hydrogen atom and is and is taken as 1 unit.
b) Discovery of sub atomic particles :In 1900, J.J.Thomson discovered the presence of the
negatively charged particles called electrons in the atom.
In 1886, E.Goldstein discovered new radiations in gas discharge
and called them canal rays. These rays were positively charged. This
later led to the discovery of the positively charged particles called
protons in the atom.
In 1932 Chadwick discovered the presence of particles having
no charge in the atom called neutrons.
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2) Structure of an atom :-
a) Thomson’s model of an atom :-
According to Thomson an atom is similar to a Christmas pudding.
The pudding had positive charge and the electrons having negative
charge were like plums on the pudding.
He proposed that :i) An atom consists of a positively charged sphere and the electrons
are
embedded in it.
ii) The negative and positive charges are equal in magnitude So the
atom as a whole is electrically neutral.
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b) Rutherford’s model of an atom :Rutherford’s alpha scattering experiment :Rutherford allowed a beam of fast moving alpha particles ( α –
particles) having positive charge to fall on a thin gold foil. He
observed that :i) Most of the α – particles passed straight through the gold foil.
ii) Some of the α – particles were slightly deflected by small
angles.
iii) Very few α – particles appeared to rebound.
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Conclusions from Rutherford’s alpha scattering
experiment :i) Most of the space inside an atom is empty. (because most of the α –
particles passed straight through the gold foil.)
ii) The atom had a small nucleus having positive charge. ( because
some of the α – particles having positive charge were slightly
deflected by small angles.)
iii) The size of the nucleus is very small compared to the size of the
atom. (because very few α – particles appeared to rebound and
most of the positive charge and mass of the atom is in the nucleus.)
Rutherford’s model of an atom :i) An atom has a positively charged nucleus at its centre and most of
the mass of the atom is in the nucleus.
ii) The electrons revolve around the nucleus in different orbits.
iii) The size of the nucleus is very small compared to the size of the
atom.
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Defects of Rutherford’s model of the atom :Any particle in a circular orbit would undergo acceleration and
during acceleration the charged particle would radiate energy. So the
revolving electrons would lose energy and fall into the nucleus and
the atom would be unstable. We know that atoms are stable.
Rutherford’s model
of an atom
Negatively charged
electron
-
Negatively charged
electrons in orbits
around the nucleus
+
Very small positively
charged nucleus
Positively charged
nucleus
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c) Bohr’s model of an atom :i) An atom has a positively charged nucleus at its centre and most of
the mass of the atom is in the nucleus.
ii) The electrons revolve around the nucleus in special orbits called
discrete orbits.
iii) These orbits are called shells or energy levels and are represented
by the letters K, L, M, N etc. or numbered as 1, 2, 3, 4, etc.
iv) While revolving in the discrete orbits the electrons do not radiate
energy.
Shells or energy levels in an atom
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3) Distribution of electrons in different shells :The distribution of electrons in the different shells was suggested
by Bhor and Bury. The following are the rules for filling electrons in
the different shells.
i) The maximum number of electrons in a shell is given by
the formula 2n2 where n is the number of the shell 1, 2, 3
etc.
First shell or K shell can have = 2n2 = 2 x 12 = 2x1x1 = 2 electrons
Second shell or L shell can have = 2n2 = 2 x 22 = 2x2x2 = 8 electrons
Third shell or M shell can have = 2n2 = 2 x 32 = 2x3x3 = 18 electrons
Fourth shell or N shell can have = 2n2 = 2 x 42 = 2x4x4 = 32 electrons
and so on.
ii) The maximum number of electrons that can be filled in
the outermost shell is 8.
iii) Electrons cannot be filled in a shell unless the inner
shells are filled.
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Composition of the atoms of the first eighteen elements :Name of
element
Symbol
Atomic
Number
Number of
Protons
Number of
Neutrons
Number of
Electrons
Distribution
Of Electrons
K L M N
Valency
Hydrogen
H
1
1
-
1
1
-
-
-
1
Helium
He
2
2
2
2
2
-
-
-
0
Lithium
Li
3
3
4
3
2
1
-
-
1
Beryllium
Be
4
4
5
4
2
2
-
-
2
Boron
B
5
5
6
5
2
3
-
-
3
Carbon
C
6
6
6
6
2
4
-
-
4
Nitrogen
N
7
7
7
7
2
5
-
-
3
Oxygen
O
8
8
8
8
2
6
-
-
2
Fluorine
F
9
9
10
9
2
7
-
-
1
Neon
Ne
10
10
10
10
2
8
-
-
0
Sodium
Na
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11
12
11
2
8
1
-
1
Magnesium
Mg
12
12
12
12
2
8
2
-
2
Aluminium
Al
13
13
14
13
2
8
3
-
3
Silicon
Si
14
14
14
14
2
8
4
-
4
Phosphorus
P
15
15
16
15
2
8
5
-
3,5
Sulphur
S
16
16
16
16
2
8
6
-
2
Chlorine
Cl
17
17
18
17
2
8
7
-
Argon
Ar
18
18
22
18
2
8
8
-
1
13
0
Atomic structure of the first eighteen elements :-
H
He
Li
Be
B
C
N
O
F
Ne
Na
Mg
Al
Si
P
S
Cl
Ar
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4) Valency :Valency is the combining capacity of an atom of an element.
The electrons present in the outermost shell of an atom are
called valence electrons.
If an atom’s outermost shell is completely filled, they are inert
or least reactive and their combining capacity or valency is zero.
Of the inert elements Helium atom has 2 electrons in the
outermost shell and the atoms of other elements have 8 electrons in
their outermost shell. Atoms having 8 electrons in their outermost
shell is having octet configuration and are stable.
If an atom’s outermost shell is not completely filled it is not
stable. It will try to attain stability by losing, gaining or sharing
electrons with other atoms to attain octet configuration.
The number of electrons lost, gained or shared by an atom to
attain octet configuration is the combining capacity or valency of the
element
Eg :- Hydrogen, Lithium, Sodium atoms can easily lose 1 electron
and become stable. So their valency is 1. Magnesium can easily lose
2 electrons. So its valency is 2. Aluminiun can easily lose 3 electrons.
So its valency is 3. Carbon shares 4 electrons. So its valency is 4.
Fluorine can easily gain 1 electron and become stable. So
its valency is 1. Oxygen can easily gain 2 electrons. So its valency is
2. Nitrogen can easily gain 3 electrons. So its valency is 3.
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5) Atomic number and Mass number :a) Atomic number (Z) :-
The atomic number of an element is the number of protons present in the
nucleus of the atom of the element.
All the atoms of an element have the same atomic number.
Eg :- Hydrogen – Atomic number = 1 (1 proton)
Helium
- Atomic number = 2 (2 protons)
Lithium
- Atomic number = 3 (3 protons)
b) Mass number (A) :-
The mass number of an element is the sum of the number of protons and
neutrons (nucleons) present in the nucleus of an atom of the element.
The mass of an atom is mainly the mass of the protons and neutrons in the
nucleus of the atom.
Eg :- Carbon – Mass number = 12 (6 protons + 6 neutrons) Mass = 12u
Aluminium – Mass number = 27 (13 protons + 14 neutrons) Mass = 27u
Sulphur – Mass number = 32 (16 protons + 16 neutrons) Mass = 32u
In the notation of an atom the
atomic number and mass number
Eg :N
are written as :-
Mass number
Symbol of
Atomic number
element
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5) Isotopes :Isotopes are atoms of the same element having the
same atomic numbers but different mass numbers.
Eg :- Hydrogen has three isotopes. They are Protium,
Deuterium (D) and Tritium (T).
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1
H
2
1
3
H
1
H
Protium
Deuterium
Tritium
Carbon has two isotopes. They are :12
6
C
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6
C
Chlorine
has two
isotopes They are :35
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Cl
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Cl
17
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6) Isobars :Isobars are atoms of different elements having different atomic
numbers but same mass numbers.
These pairs of elements have the same number of nucleons.
Eg :- Calcium (Ca) – atomic number - 20 and Argon (Ar) – atomic
number 18 have different atomic numbers but have the same
mass numbers – 40.
40
20
Ca
40
18
Ar
Iron (Fe) and Nickel (Ni) have different atomic numbers but
have the same atomic mass numbers – 58.
58
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Fe
58
27
Ni
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Electronic
• Electronics is the branch
of physics, engineering and technology dealing with electrical
circuits that involve active electrical components such
as vacuum tubes, transistors,diodes and integrated circuits,
and associated passive interconnection technologies.
The nonlinear behaviour of active components and their ability
to control electron flows makes amplification of weak signals
possible and is usually applied to information and signal
processing. Similarly, the ability of electronic devices to act
as switches makes digital information processing possible.
Interconnection technologies such as circuit boards,
electronics packaging technology, and other varied forms of
communication infrastructure complete circuit functionality
and transform the mixed components into a working system.
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Faraday Basics
• Faraday's law of induction is
one of the important concepts
of electricity. It looks at the way
changingmagnetic fields can
cause current to flow in wires.
Basically, it is a formula/concept
that describes how potential
difference (voltage difference) is
created and how much is
created. It's a huge concept to
understand that the changing of
a magnetic field can create
voltage
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Stepper motor
 A stepper motor is a
brushless, synchronous
electric motor that
converts digital pulses
into mechanical shaft
rotation. Every
revolution of the stepper
motor is divided into a
discrete number of
steps, in many cases 200
steps, and the motor
must be sent a separate
pulse for each step.
 Types of Step
Motors
 There are three
basic types of step
motors: variable
reluctance,
permanent magnet,
and hybrid.
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• Stepper motor are designed to rotate in a
number of precisely defined steps.
• The number of steps per revolution are defined
by the number of magnetic poles in the motor
• They usually controlled by a microprocessor
electronically switching a set of stationary
electromagnets.
• Stepper motors are used in automotive for
applications such as instrument panel controls
and air conditioner controls.
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1.2 Understand the operation
principle of the free electron
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Electrical current
• Current refers to the electrons passing any given
point in the circuit in one second. Its flow on a
wire or conductor, measured in amperes or amps.
Electrical current is like the rate that water flows
through a pipe. If there is a large volume of water
to flow, a big pipe is needed.
• Current will increased as pressure or voltage is
increased-provided circuit resistance remains
constant.
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voltage
• For electric current to flow, the electrons
need a complete pathway, or circuit. To
make them move, there must be a force. It
is called electromotive force or EMF, also
known as voltage.
• The larger the charge at the positive
terminal, the more strongly it attracts
free electrons. This attraction acts as a
force driving the electrons along. The
greater the force, the stronger the
electrical current.
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Resistance
• The ohm is the resistance of a conductor such
that a constant current of 1 ampere in it
produces a voltage of 1 volt between its ends.
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The resistance of a conductor is
affected by the following factors:
• Length of the conductor
• Area of cross section of the
conductor
• Electrical Resistivity of Substances
• Effect of Temperature
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Flow in one direction
 Free electrons are necessary for electric
current, but for those electrons to move, they
need a complete pathway, or circuit, and there
must be a force to make them move. The force
from a battery sets free electrons moving.
 Like charges repel, so the negative electrons
are repelled from the negative terminal. Unlike
charges attract, so the electrons are also
attracted towards the positive terminal.
 They flow in one direction only. This is
called direct current or DC. Most circuits in
motor vehicles use direct current.
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1.3 Understand the
operation principle of
the electronic
components
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Diode
• A diode can be thought of as the electronic
version of a one-way valve. By restricting the
direction of movement of charge carriers, it
allows an electric current to flow in one
direction, but essentially blocks it in the
opposite direction.
• A semiconductor diode has a single p-n junction.
If it is connected to a current source, with the
p region connected to a negative pole, and the
n-region to a positive pole, the holes will be
attracted towards the negative pole, and the
electrons to the positive pole.
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Resistor
 Resistors are electrical components that resist a current running
through them.
 Putting a resistor in a circuit causes a drop in voltage across
the resistor. So resistors are commonly used to control the voltage
that reaches various components.
 It is also important to remember that each electrical component
also has a resistance of its own.
 Most resistors that can carry large currents contain a coil of highresistance wire wound around a ceramic former to dissipate heat.
 Resistance is measured in ohms, represented by a Greek letter,
omega, and so resistors are rated in ohms as well, to indicate how
strongly they will oppose any current flowing through them.
 Resistors also have a wattage rating. This is because resistors work
by converting some of the electrical energy passing through them
into heat.
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Resistor ratings
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Variable resistors
• Variable resistors can be adjusted with a control so
that the resistance changes, and are called rheostats or
potentiometers. An audio volume control knob on an
amplifier would be an example of a potentiometer.
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Thermistors
• Thermistors are semiconductor resistors. Their
electrical resistance varies according to
temperature. This makes them suitable for
temperature measurement, and for electronic
control operations.
• There are two main types of thermistor – NTC
(Negative Temperature Coefficient) resistors,
and PTC (Positive Temperature Coefficient)
resistors.
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• NTC resistors have lower resistance at high
temperatures, which means they conduct current
more readily when they are hot than when they
are cold. NTC resistors are commonly used in
temperature sensors in engine management
systems.
• PTC resistors have higher resistance at high
temperature, which means they conduct current
less readily when they are hot than when they
are cold. This makes them useful as current
limiting protective devices in circuits, instead of
fuses. As the current increases, the heat
generated by the resistor increases, which
reduces the amount of current passed.
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PTC
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NPC
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Transistor
 Transistors are semiconductor devices used as
switches, and to amplify currents. They are a key
component in almost any electronic device.
 There are two kinds, npn and pnp. The
npn transistorhas a p-type semiconductor between
two n-type semiconductors. A pnp transistor has
an n-type, between two p-types.
 Each of the three regions has a terminal. The
center region is always called the base. The outer
regions are the collector, and the emitter. In the
symbol, the emitter is the terminal with the arrow.
always pointing to the negative material.
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• In a circuit, npn transistors can act as a switch. If
the control switch is open, the depletion layer at
one pn-junction is blocking current from flowing
through the transistor and driving the load.
• With a closed control switch, a small current
flows through the emitter-base pn-junction. The
base has only a limited number of charge carriers,
so extra ones flow across the emitter-collector
pn-junction, letting current operate the load.
The transistor then operates as a low-resistance
conductor. A small current through the base lets
larger current flow across the emitter-collector
junction. The transistor is then said to be turned
on.
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Transformer
 A transformer is a simple electrical machine most commonly used to
change voltage levels from one value to another in different parts of
electrical circuits.
 A transformer can step voltage up or down. A basictransformer has
two tightly coiled loops of wire called 'windings' coupled together, a
primary winding and a secondary winding. These are usually wound
around a laminated soft iron core. When a current is introduced into
the primary winding, a voltage is induced in the secondary winding.
Varying the relative number of winding turns in the two windings
determines the variation between the input and output voltages.
 A step up transformer increases the voltage from the primary
winding to the secondary winding, while a step
down transformer decreases the voltage from the primary winding
to the secondary winding.
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