All in one.pptx

CHAPTER ONE
Introduction to Engineering Materials

1. Classification of materials
The engineering materials are classified as follows:
1.1 Metals: Metals are the iron groups which includes all types of iron and steel. Metals are dense, shiny elements
that are good conductors of heat and electricity. Most metals are malleable and ductile and are, in general,
denser than the other elemental substances. Example of metals are iron, aluminum, copper, zinc, lead
etc.
Metals also devided into:
i) Ferrous metals: are metals contain iron and are magnetic. They are prone to rust and therefore require a
protective finish, which is sometimes used to improve the aesthetics of the product it is used for as well.
Example of ferrous metals are cast iron, wrought iron and steel and alloys of ferrous metal are silicon,
steel, high speed steel, spring steel etc.
ii) Non-ferrous metals: are metals that do not contain iron and are not magnetic. They do not rust. Examples
of non- ferrous metals are copper, aluminum, zinc, lead etc. and alloys of non- ferrous metals are Brass,
bronze, duralumin etc.
1.2 Non metals: Non-metals are those which lack all the metallic attributes. They are good insulators of heat and
electricity. They are mostly gases and sometimes liquid. Some are even solid at room temperatures
like Carbon, Sulphur and phosphorus. Examples of Non-metals are leather, rubber, plastics,
asbestos, carbon etc.

1.2 Other classification of engineering materials:
Engineering materials can also be classified as below-
a) Metals and Alloys
b) Ceramic Materials
c) Organic Materials
a) Metals and Alloys
Metals are polycrystalline bodies which have a number of differentially oriented fine crystals. Normally
major metals are in solid states at normal temperature. However, some metals such as mercury are also in
liquid state at normal temperature.
Pure metals are having very a low mechanical strength, which sometimes does not match with the
mechanical strength required for certain applications. To overcome this draw back alloys are used.
Alloys are the composition of two or more metals or metal and non-metals together. Alloys are having good
mechanical strength, low temperature coefficient of resistance.
Example: Steels, Copper, Aluminium,Brass, Bronze, Gunmetal, Invar. Super Alloys etc.

b) Ceramic Materials
Ceramic materials are non-metallic solids. These are made of inorganic compounds such as Oxides,
Nitrides, Silicates and Carbides. Ceramic materials possess exceptional Structural, Electrical,
Magnetic, Chemical and Thermal properties. These ceramic materials are now extensively used in
different engineering fields.
Examples: Silica, glass, cement, concrete, garnet, Magnesium oxide (MgO), Cadmium sulfide(Cds),
Zinc oxide (Zno), Silicon Carbide (sic) etc.
c) Organic Materials (Polymers)
All organic materials are having carbon as a common element. In organic materials carbon is
chemically combined with oxygen, hydrogen and other non-metallic substances. Generally organic
materials are having complex chemical bonding.
Example: Plastics, PVC, Synthetic Rubbers etc.

1.3 A composite material: is a combination of two materials with different physical and chemical
properties. When they are combined they create a material which is specialised to do a certain job, for
instance to become stronger, lighter or resistant to electricity.
They can also improve strength and stiffness. The reason for their use over traditional materials is because
they improve the properties of their base materials and are applicable in many situations.

No. Property Metals Non-Metals
1. Structure
All metals are having crystalline
structure
All Non-metals are having amorphic &
mesomorphic structure
2. State
Generally metals are solid at normal
temperature
State varies material to material. Some
are gas state and some are in solid
state at normal temperature.
3.
Valance electrons and
conductivity
Valance electrons are free to move
within metals which makes them
good conductor of heat & electricity
Valence electrons are tightly bound
with nucleus which are not free to
move. This makes them bad conductor
of heat & electricity
4. Density High density Low density
5. Strength High strength Low strength
6. Hardness Generally hard Hardness is generally varies
7. Malleability Malleable Non malleable
8. Ductility Ductile Non ductile
9. Brittleness Generally non brittle in nature Brittleness varies material to material
10. Lustre Metals possess metallic lustre
Generally do not possess metallic
lustre (Except graphite & iodine)
2. Difference between Metals and Non Metals

What are material properties?
Properties are factors that qualitatively or quantitatively influence the response of a given material to the
imposition of stimuli and constraints.
e.g., forces, temperature, etc. Similarly, properties make a material suitable or unsuitable for a particular
industrial use. In other words, when we refer to the properties of a material, we are talking about characteristics
that we can recognize, measure or test.
1. Physical properties of materials
2. Mechanical properties of materials
3. Electrical properties of materials
4. Magnetic properties of materials
5. Chemical properties of materials
3. Properties of materials

1. Physical properties of materials
Physical properties are those that can be observed without changing the composition of the material. For
example, some of the most important physical properties of metals are:
•Density: The density of a substance is its mass per unit volume. The symbol most often used for density is ρ
although the Latin letter D can also be used.
•Boiling point:The boiling point of a liquid varies according to the applied pressure; the normal boiling point is the
temperature at which the vapour pressure is equal to the standard sea-level atmospheric pressure (760 mm of
mercury). At sea level, water boils at 100° C (212° F).
•Melting or Freezing point: Freezing point is the temperature at which a liquid becomes a solid at normal
atmospheric pressure. Alternatively, a melting point is the temperature at which a solid becomes a liquid at normal
atmospheric pressure.
•Linear coefficient of expansion: is a material property which characterizes the ability of a matrial to expand
under the effect of each degree rise in temperature. It tells you how much the developed part will remain
dimensionally stable under temperature variations.

•Thermal conductivity: Thermal conductivity refers to the inherent ability of a material to transfer or
conduct heat.
•Electrical resistivity: Eletrical resistivity, represented by the Greek letter ρ (rho), is a measure of the
resistance of a specific material of a given size, to the electrical current conduction that flows through it.
The SI unit of electrical resistivity is expressed in ohm-metres (Ωm).

2. Mechanical properties of materials
The following are the mechanical properties of materials.
They are those that determine the
behavior of a material under the forces
applied to it and reflect the relationship
between its response to a load and the
deformation it undergoes.

R
R = V/I or,
R = ρ(L/A)
V = Voltage, I = Current, ρ =
Resistivity

CHAPTER TWO
Introduction to Conducting Materials

2.1 Conducting materials:
A conductor, or electrical conductor, is a substance or material that allows electricity to flow through it. In a
conductor, electrical charge carriers, usually electrons or ions, move easily from atom to atom when voltage is
applied.
2.2 Resistivity and factors affecting resistivity
2.2.1 Resistance: Every conductor possesses some resistance. It may be very high (insulator) or maybe low
(conductor). Resistance is effectively helpful in controlling the flow of electric current. So before understanding
resistivity and what are the factors affecting resistivity, you have to understand resistance. What is it, and how
it works?
Resistance of a material can be measured by: R = ρ(L/A)
Where,
L = length of the conductor
A = area of the cross-section of the conductor
ρ = resistivity

2.2.2 What is resistivity?
The electrical resistivity of a particular conductor material is a measure of how strongly the material
opposes the flow of electric current through it. This resistivity factor, sometimes called its “specific
electrical resistance”, enables the resistance of different types of conductors to be compared to one
another at a specified temperature according to their physical properties without regards to their
lengths or cross-sectional areas. Thus the higher the resistivity value of ρ the more resistance and vice
versa.
From the above equation, resistance (R) is directly proportional to the (L) length of the conductor and (ρ)
resistivity. And the resistance (R) is inversely proportional to (A) area of the cross-section of the conductor.
So, the resistance of a material is affected by its length, area of cross-section, material, and temperature.

2.3 Factors effecting the resistivity of electrical materials are listed below:
I. Temperature
II. Alloying
III. Mechanical stressing
IV. Age Hardening
V. Cold Working
2.3.1 Temperature
The resistivity of materials changes with temperature. Resistivity of most of the metals increase with temperature.
The change in the resistivity of material with change in temperature is given by formula as:
Where,
ρt1 is the resistivity of material at temperature of t1
o C and
ρt2 is the resistivity of material at temperature of t2
oC
α1 is temperature coefficient of resistance of material at temperature of t1
o C.
If the value of α1 is positive, the resistivity of material is increase.

The resistivity of metals increase with increase of temperature. Means the metals are having positive
temperature coefficient of resistance. Several metals exhibit the zero resistivity at temperature near to
absolute zero. This phenomenon is “called the superconductivity”.
The resistivity of semiconductors and insulators decrease with increase in temperature. Means the
semiconductors and insulators are having negative temperature coefficient of resistance.
2.3.2 Alloying
Alloying is a solid solution of two or more metals. Alloying of metals is used to achieve some mechanical
and electrical properties. The atomic structure of a solid solution is irregular as compared to pure metals.
Due to which the electrical resistivity of the solid solution increases more rapidly with increase of alloy
content. A small content of impurity may increase the resistivity of metal considerably. Even the impurity
of low resistivity increases the resistivity of base metal considerably. For example the impurity of silver
(having lowest resistivity among all metals) in copper increase the resistivity of copper.

2.3.3 Mechanical Stressing
Mechanical stressing of the crystal structure of material develops the localized strains in the material crystal
structure. These localized stains disturb the movement of free electrons through the material. Which results in
an increase in resistivity of the material. Subsequently, annealing, of metal reduces the resistivity of metal.
Annealing of metal, relieve the mechanical stressing of material due to which the localized stains got removed
from the crystal structure of the metal. Due to which the resistivity of metal decrease. For example, the
resistivity of hard drawn copper is more as compared to annealed copper.
2.3.4 Age Hardening
Age hardening is a heat treatment process used to increase the yield strength and to develop the ability in alloys
to resist the permanent deformation by external forces. Age hardening is also called “Precipitation Hardening”.
This process increases the strength of alloys by creating solid impurities or precipitate. These created solid
impurities or precipitate, disturb the crystal structure of metal which interrupts the flow of free electrons
through metal/Due to which the resistivity of metal increases.

2.3.5 Cold Working
Cold working is a manufacturing process used to increase the strength of metals. Cold working is also known as “Work
hardening” or “Strain hardening”. Cold working is used to increase the mechanical strength of the metal. Cold working
disturbs the crystal structure of metals which interfere with the movement of electrons in metal, due to which the
resistivity of metal increases.
3. Conducting Materials:
Materials used for conducting electricity are known as Conducting materials. These materials play a vital role in
Electrical Engineering. It is interesting to know the applications of these materials in the field of Electrical
Engineering, like the type of materials used in Transmission lines, Electrical Machines, Starters, and Rheostats,
etc., along with different conducting materials, we will also go through their alloys.

A classification chart of conducting materials based on resistivity or conductivity
Electrical conducting materials are the basic requirement for electrical engineering products. They can be
classified as below based on Resistivity or Conductivity. .
4. Materials of low and high resistivity
4.1 Classification of conducting material based on Resistivity or Conductivity

4.1.1 Low Resistivity or High Conductivity Conducting Material
Material having low resistivity or high conductivity are very useful in electrical engineering products. These materials are
used as conductors for all kind of windings required in electrical machines, apparatus and devices. These materials are
also used as conductor in transmission and distribution of electrical energy.
Some of low resistivity or high conductivity materials and their resistivity are given below:
•Silver with resistivity of 1.58 µΩ -cm
•Copper with resistivity of 1.68 µΩ -cm
•Gold with resistivity of 2.21 µΩ -cm
•Aluminum with resistivity of 2.65 µΩ -cm
4.1.2 High Resistivity or Low Conductivity Conducting Material
Materials having High resistivity or Low conductivity conducting are very useful for electrical engineering products.
These material are used to manufacture the filaments for incandescent lamp, heating elements for electric heaters,
space heaters and electric irons etc. Some of materials having High resistivity or Low conductivity are listed below:
•Tungsten
•Carbon
•Nichrome or Bright ray – B
•Nichrome – Vor Bright ray – C
•Manganin

Chart of conducting materials based on their applications
5. Conducting materials used for different applications
Classification of Electrical Conducting Materials based on their application.

Conducting materials based on area of application
1. Materials used as conductor for coils of electrical machines
2. Materials for heating elements
3. Materials for lamp filaments
4. Material used for transmission line
5. Bimetals
6. Electrical Contact Materials
7. Electrical Carbon Materials
8. Material for Brushes used in Electrical Machines
9. Materials used for fuses

5.1 Materials Used as Conductor for Coils of Electrical Machines
Materials having low resistivity or high conductivity such as copper, silver and aluminum can be used for making
coils for electrical machines. However, looking to optimum conductivity, mechanical strength and cost, copper is
much suitable for making coils for electrical machines.
5.2 Materials for Heating Elements
Materials having high resistivity or low conductivity such as Nichrome, Kanthal, Cupronickel and Platinum etc.
are used for making heating elements. Materials used for heating elements must possess following properties-
•High melting point
•Free from oxidation in operating atmosphere
•High tensile strength
•Sufficient ductility to draw the metal or alloy in the form of wire

5.3 Materials for Lamp Filaments
Materials having high resistivity or low conductivity such as Carbon, Tantalum and Tungsten etc. are used for making
incandescent lamp filament. Materials used for making incandescent lamp filament must possess following properties-
• High melting point
• Low vapour pressure
• Free from oxidation in inert gas (argon, nitrogen etc.)
medium at operating temperature
• High resistivity
• Low thermal coefficient of expansion
• Low temperature coefficient of resistance
• Should have high young modulus and tensile strength
• Sufficient ductility so that can be drawn in the form of very thin wire
• Ability to be converted in the shape of filament
• High fatigue resistance against thermally induced fluctuating stresses
• Cost should minimum

5.4 Material Used for Transmission Line
Materials used for making conductor for transmission line must possess following properties
•High conductivity
•High tensile strength
•Light weight
•High resistance to corrosion
•High thermal stability
•Low coefficient of thermal expansion
•Low cost
Materials use for transmission lines are listed below:
•Copper
•Aluminum
•Cadmium-Copper alloys
•Phosphor bronze
•Galvanized steel
•Steel core copper
•Steel core aluminum
5.6 Bimetals
Many combinations of metals with different “Coefficient of linear thermal expansion” can be used to form the
bimetals. Some of the commonly used combinations for making bimetallic strips are listed below-
•Iron, nickel, constantan (high “Coefficient of linear thermal expansion”)
•Alloy of iron and nickel (low “Coefficient of linear thermal expansion”)

5.7 Electrical Contact Materials
Electrical contact materials refer to a class of metals that are used in the electrical interfaces of electrical
connectors and electrical switches. While selecting a suitable material for electrical contact, we have to
consider basic factors. Some of most important factors of these are listed below :
•Contact resistance
•Contact force
•Voltage and current
5.8 Electrical Carbon Materials
Carbon in widely used in electrical engineering. Electrical carbon materials are manufactured from graphite and
other forms of carbon. Carbon is having following applications in electrical Engineering
•For making filament of incandescent lamp
•For making electrical contacts
•For making resistors
•For making brushes for electrical machines such as DC
machines, alternators.
•For making battery cell elements
•Carbon electrodes for electric furnaces
•Arc lighting and welding electrodes
•Component for vacuum valves and tubes
•For makings parts for telecommunication equipment’s

5.9 Material for Brushes Used in Electrical Machines
Before selecting the material for brushes, we should keep in our mind the following requirements in a brush :
•Contact resistance
•Thermal stability
•Lubrication properties
•Mechanical strength
•Low brittleness
Material used for Brushes in electrical machines are listed as:
•Carbon
•Natural graphite
•Electro graphite
•Metal graphite
•Copper

5.10 Materials Used for Fuse Elements
A fuse commonly consists of a current-conducting strip or wire of easily fusible metal that melts, and
thus interrupts the circuit of which it is a part, whenever that circuit is made to carry a current larger
than that for which it is intended.
Fuse element is primary requirement of a fuse unit. The fuse element should have following properties-
Low resistance – to avoid the undesirable voltage drop across the fuse element, so that it should effects the normal
functioning or performance of circuit or device or equipment.
Low melting point – the fuse element must have low melting point. So that it blow out due to heating by excess
current during over load or short circuit.
Different types of metals and alloys are used for fuse element. Some of these elements are listed below –
•Aluminum
•Lead and tin
•Copper
•Silver
•Rose’Alloys
•Wood alloys

Many metals and metallic alloys are suitable to be used in thermocouples as thermoelectric effect
occurs when two materials are put in contact forming a thermal junction. However, thermocouple
materials are chosen according to some important characteristics: maximum sensibility over the
entire operating range, long-term stability including high temperatures, cost, and compatibility with
the available instrumentation. Most often thermocouple materials are metallic alloys with two or
more components to achieve the desired characteristics to a range of temperatures.
6.1 What is a Thermocouple?
A Thermocouple is a sensor used to measure temperature. A thermocouple consists of two dissimilar metals,
joined together at one end, which produce a small voltage when heated (or cooled). This voltage is measured and
used to determine the temperature of the heated metals. The voltage for any one temperature is unique to the
combination of metals used.
6. Thermocouple Material

6.2 Types of Thermocouple?
Thermocouples are available in different combinations of metals, usually referred to by a letter, e.g. J, K
etc giving rise to the terms type J thermocouple, type K thermocouple etc. Each combination has a
different temperature range and is therefore more suited to certain applications than others.

7. Superconductivity
Superconductivity is the ability of certain materials to conduct electric current with practically zero
resistance. This capacity produces interesting and potentially useful effects. For a material to behave as
a superconductor, low temperatures are required. Or
Superconductivity is the property of certain materials to conduct direct current (DC) electricity without
energy loss when they are cooled below a critical temperature (referred to as Tc). These materials also
expel magnetic fields as they transition to the superconducting state.
Superconductivity explained

If you think you can’t relate to the real-life applications of superconductors, well, here is your chance to think
again…!!!
•Superconducting magnets are used for accelerating the particles in the Large Hadron Collider.
•SQUIDs (superconducting quantum interference devices) are being used in the production of highly sensitive
magnetometers. They are generally used for the detection of land mines.
•Superconducting magnets are also used in Magnetic Resonance Imaging (MRI) machines.
•As we know due to the electrical resistance, there is a power loss while power transmission. So nowadays,
superconducting cables are used in place of ordinary cable lines to avoid power loss.
•Superconductors are also being used for the development of high-intensity Electro Magnetic Impulse (EMP). They
are used to paralyze all the electronic equipment within the range.
•Last but not least, Maglev trains work on the superconducting magnetic levitation phenomenon. Japenese Maglev
train is a real-life example of magnetic levitation.
8. Applications of Superconductors

CHAPTER 3
Semiconductor Materials

Revision: Electronic Materials
• The goal of electronic materials is to generate and control the flow
of an electrical current.
• Electronic materials include:
1. Conductors: have low resistance which allows electrical current
flow
2. Insulators: have high resistance which suppresses electrical
current flow
3. Semiconductors: can allow or suppress electrical current flow

Revision: Conductors
• Good conductors have low resistance so electrons flow
through them with ease.
• Best element conductors include:
– Copper, silver, gold, aluminum, & nickel
• Alloys are also good conductors:
– Brass & steel
• Good conductors can also be liquid:
– Salt water

Revision: Conductor Atomic Structure
• The atomic structure of good conductors
usually includes only one electron in their
outer shell.
– It is called a valence electron.
– It is easily striped from the atom, producing
current flow.
Copper Atom

Revision: Insulators
• Insulators have a high resistance so current does not flow in
them.
• Good insulators include:
– Glass, ceramic, plastics, & wood
• Most insulators are compounds of several elements.
• The insulator atoms are tightly bound to one another so
electrons are difficult to strip away for current flow.

Definition: Semiconductors
• A semiconductor is a material usually comprised of silicon, which conducts electricity more than an
insulator, such as glass, but less than a pure conductor, such as copper or aluminum. Their
conductivity and other properties can be altered with the introduction of impurities, called doping, to
meet the specific needs of the electronic component in which it resides.
• Semiconductors are the materials which have a conductivity between conductors (generally metals)
and non-conductors or insulators (such as ceramics).
• Common elements such as Gallium arsenide, carbon, silicon, and germanium are
semiconductors.
• Silicon is the best and most widely used semiconductor.
• Silicon is used in electronic circuit fabrication and gallium arsenide is used in solar cells, laser
diodes, etc.

1.1 Semiconductor range of conduciveness
The semiconductors fall somewhere midway between conductors and insulators.
1. Characteristics of semiconductors

1.2 Holes and Electrons in Semiconductors
Holes and electrons are the types of charge carriers accountable for the flow of current in
semiconductors. Holes (valence electrons) are the positively charged electric charge carrier whereas
electrons are the negatively charged particles. Both electrons and holes are equal in magnitude but
opposite in polarity.

1.3 Mobility of Electrons and Holes
In a semiconductor, the mobility of electrons is higher than that of the holes. It is mainly because of
their different band structures and scattering mechanisms.
Electrons travel in the conduction band whereas holes travel in the valence band. When an electric field is
applied, holes cannot move as freely as electrons due to their restricted movent. The elevation of electrons
from their inner shells to higher shells results in the creation of holes in semiconductors. Since the holes
experience stronger atomic force by the nucleus than electrons, holes have lower mobility.
The mobility of a particle in a semiconductor is more if;
1. Effective mass of particles is lesser
2. Time between scattering events is more
For intrinsic silicon at 300 K, the mobility of electrons is 1500 cm
2
(V∙s)
-1
and the mobility of holes is 475
cm
2
(V∙s)
-1
.

The bond model example of electrons in silicon of valency 4 is shown below. Here, when one of the
free electrons (blue dots) leaves the lattice position, it creates a hole (grey dots). This hole thus created
takes the opposite charge of the electron and can be imagined as positive charge carriers moving in the
lattice.
bond model of electrons in silicon of valency 4

1.4 Band Theory of Semiconductors
In solids, several bands of energy levels are formed due to the intermixing of atoms in solids. We call
these set of energy levels as energy bands.
1.4.1 Classification of Energy Bands
(I) Valence Band
The energy band involving the energy levels of valence electrons is known as the valence band. It is the highest occupied energy band. When
compared with insulators, the bandgap in semiconductors is smaller. It allows the electrons in the valence band to jump into the conduction band on
receiving any external energy.
(II) Conduction Band
The valence electrons are not tightly held to the nucleus due to which a few of these valence electrons leave the
outermost orbit even at room temperature and become free electrons. The free electrons conduct current in conductors
and are therefore known as conduction electrons. The conduction band is one that contains conduction electrons and
has the lowest occupied energy levels.
(III) Forbidden Energy Gap
The gap between the valence band and the conduction band is referred to as forbidden gap. As the name suggests, the
forbidden gap doesn’t have any energy and no electrons stay in this band. If the forbidden energy gap is greater, then
the valence band electrons are tightly bound or firmly attached to the nucleus. We require some amount of external
energy that is equal to the forbidden energy gap.

Energy Bands Semiconductors, Conductors, and Insulators (cont.)
at room temperature
25°
81
 Energy gap-the difference between the energy levels of any two orbital shells
 Band-another name for an orbital shell (valence shell=valence band)
 Conduction band –the band outside the valence shell where it has free electrons.
 eV (electron volt) – the energy absorbed by an electron when it is subjected to a 1V difference of potential

What is Fermi Level?
The highest energy level that an electron can occupy at the absolute zero temperature is known as the Fermi Level. The
Fermi level lies between the valence band and conduction band because at absolute zero temperature the electrons are all
in the lowest energy state. Due to the lack of sufficient energy at 0 Kelvin, the Fermi level can be considered as the sea of
fermions (or electrons) above which no electrons exist. The Fermi level changes as the solids are warmed and as electrons
are added to or withdrawn from the solid.
1.5 Fermi Level in Semiconductors
In a p-type semiconductor, there is an increase in the density of unfilled states. Thus, accommodating more electrons at
the lower energy levels. However, in an n-type semiconductor, the density of states increases, therefore, accommodating
more electrons at higher energy levels.

1.6 Semiconductor Valence Orbit
• The main
characteristic of a
semiconductor
element is that it has
four electrons in its
outer or valence
orbit.

1.7 Crystal Lattice Structure
• The unique capability of
semiconductor atoms is their
ability to link together to form a
physical structure called a
crystal lattice.
• The atoms link together with
one another sharing their outer
electrons.
• These links are called covalent
bonds.
2D Crystal Lattice Structure

1.8 Semiconductors can be Insulators
• If the material is pure semiconductor material like silicon, the crystal lattice
structure forms an excellent insulator since all the atoms are bound to one
another and are not free for current flow.
• Good insulating semiconductor material is referred to as intrinsic.
• Since the outer valence electrons of each atom are tightly bound together with
one another, the electrons are difficult to dislodge for current flow.
• Silicon in this form is a great insulator.
• Semiconductor material is often used as an insulator.

1.9 Semiconductors can be Conductors
• An impurity, or element like arsenic,
has 5 valence electrons.
• Adding arsenic (doping) will allow
four of the arsenic valence electrons
to bond with the neighboring silicon
atoms.
• The one electron left over for each
arsenic atom becomes available to
conduct current flow.
• To make the semiconductor conduct electricity, other atoms called impurities
must be added.
• “Impurities” are different elements.
• This process is called doping.

1.10 Resistance Effects of Doping
• If you use lots of arsenic atoms for doping, there will be lots of extra electrons so
the resistance of the material will be low and current will flow freely.
• If you use only a few boron atoms, there will be fewer free electrons so the
resistance will be high and less current will flow.
• By controlling the doping amount, virtually any resistance can be achieved.

Another Way to Dope
• You can also dope a semiconductor material
with an atom such as boron that has only 3
valence electrons.
• The 3 electrons in the outer orbit do form
covalent bonds with its neighboring
semiconductor atoms as before. But one
atom is missing from the bond.
• This place where a fourth electron should be
is referred to as a hole.
• The hole assumes a positive charge so it
can attract electrons from some other
source.
• Holes become a type of current carrier like
the electron to support current flow.

2. Properties of Semiconductors
Semiconductors can conduct electricity under preferable conditions or circumstances. This unique property makes it an
excellent material to conduct electricity in a controlled manner as required.
Unlike conductors, the charge carriers in semiconductors arise only because of external energy (thermal agitation). It
causes a certain number of valence electrons to cross the energy gap and jump into the conduction band, leaving an
equal amount of unoccupied energy states, i.e. holes. Conduction due to electrons and holes are equally important.
Resistivity: 10
-5
to 10
6
Ωm
Conductivity: 10
5
to 10
-6
mho/m
Temperature coefficient of resistance: Negative
Current Flow: Due to electrons and holes
Why does the Resistivity of Semiconductors go down with Temperature?
The difference in resistivity between conductors and semiconductors is due to their difference in charge carrier density.
The resistivity of semiconductors decreases with temperature because the number of charge carriers increases rapidly
with increase in temperature, making the fractional change i.e. the temperature coefficient negative.

3. Some Important Properties of Semiconductors are:
1. Semiconductor acts like an insulator at Zero Kelvin. On increasing the temperature, it works as a conductor.
2. Due to their exceptional electrical properties, semiconductors can be modified by doping to make semiconductor
devices suitable for energy conversion, switches, and amplifiers.
3. Lesser power losses.
4. Semiconductors are smaller in size and possess less weight.
5. Their resistivity is higher than conductors but lesser than insulators.
6. The resistance of semiconductor materials decreases with the increase in temperature and vice-versa.

Types of Semiconductor Materials
• The silicon doped with extra electrons is called an “N type”
semiconductor.
“N” is for negative, which is the charge of an electron.
• Silicon doped with material missing electrons that produce
locations called holes is called “P type” semiconductor.
“P” is for positive, which is the charge of a hole.

Current Flow in N-type Semiconductors
• The DC voltage source has a positive
terminal that attracts the free electrons
in the semiconductor and pulls them
away from their atoms leaving the
atoms charged positively.
• Electrons from the negative terminal of
the supply enter the semiconductor
material and are attracted by the
positive charge of the atoms missing
one of their electrons.
• Current (electrons) flows from the
positive terminal to the negative
terminal.

Current Flow in P-type Semiconductors
• Electrons from the negative supply
terminal are attracted to the positive
holes and fill them.
• The positive terminal of the supply
pulls the electrons from the holes
leaving the holes to attract more
electrons.
• Current (electrons) flows from the
negative terminal to the positive
terminal.
• Inside the semiconductor current flow
is actually by the movement of the
holes from positive to negative.

In Summary
• In its pure state, semiconductor material is an excellent insulator.
• The commonly used semiconductor material is silicon.
• Semiconductor materials can be doped with other atoms to add or subtract
electrons.
• An N-type semiconductor material has extra electrons.
• A P-type semiconductor material has a shortage of electrons with vacancies
called holes.
• The heavier the doping, the greater the conductivity or the lower the resistance.
• By controlling the doping of silicon the semiconductor material can be made as
conductive as desired.

Types of Semiconductors
Semiconductors can be classified as:
1. Intrinsic Semiconductor.
2. Extrinsic Semiconductor.
Extrinsic Semiconductors are further classified as:
a. n-type Semiconductors.
b. p-type Semiconductors.

Intrinsic Semiconductor
• Semiconductor in pure
form is known as Intrinsic
Semiconductor.
• Ex. Pure Germanium, Pure
Silicon.
• At room temp. no of
electrons equal to no. of
holes.
Si
Si
Si
Si
Si
Si
Si
Si
Si
FREE ELECTRON
HOLE
Fig 1.

Intrinsic semiconductor energy band diagram
Fermi level lies in the middle
Conduction Band
Valence Band
Energy
in
ev FERMI
LEVEL
Fig 2.

Extrinsic Semiconductor
• When we add an impurity to pure semiconductor to
increase the charge carriers then it becomes an Extrinsic
Semiconductor.
• In extrinsic semiconductor without breaking the covalent
bonds we can increase the charge carriers.

Comparison of semiconductors
1. It is in pure form.
2. Holes and electrons are
equal.
1. It is formed by adding
trivalent or pentavalent
impurity to a pure
semiconductor.
2. No. of holes are more in p-
type and no. of electrons
are more in n-type.

(Cont.,)
3. Fermi level lies in
between valence and
conduction Bands.
4. Ratio of majority and
minority carriers is
unity.
3. Fermi level lies near
valence band in p-type and
near conduction band in n-type.
4. Ratio of majority and
minority carriers are equal.

Comparison between n-type and p-type
semiconductors
N-type
• Pentavalent impurities
are added.
• Majority carriers are electrons.
• Minority carriers are
holes.
• Fermi level is near the conduction
band.
P-type
• Trivalent impurities are added.
• Majority carriers are holes.
• Minority carriers are electrons.
• Fermi level is near the valence
band.

N-type Semiconductor
• When we add a pentavalent impurity to pure
semiconductor we get n-type semiconductor.
As Pure
si
N-type
Si

N-type Semiconductor
• Arsenic atom has 5 valence electrons.
• Fifth electron is superfluous, becomes free electron and
enters into conduction band.
• Therefore pentavalent impurity donates one electron
and becomes positive donor ion. Pentavalent impurity
known as donor.

P-type Semiconductor
• When we add a Trivalent impurity to pure semiconductor
we get p-type semiconductor.
Ga
Pure
si
P-type
Si

P-type Semiconductor
• Gallium atom has 3 valence electrons.
• It makes covalent bonds with adjacent three electrons of
silicon atom.
• There is a deficiency of one covalent bond and creates a
hole.
• Therefore trivalent impurity accepts one electron and
becomes negative acceptor ion. Trivalent impurity known
as acceptor.

Carriers in P-type Semiconductor
• In addition to this, some of the covalent bonds break due
temperature and electron hole pairs generates.
• Holes are majority carriers and electrons are minority
carriers.

P and N type Semiconductors
+
+
+
+ + +
+
+
+ +
+
N
- -
-
-
-
- -
-
-
-
-
P Acceptor ion Donor ion
Minority electron Minority hole
Majority holes Majority electrons

Comparison of semiconductors
1. It is in pure form.
2. Holes and electrons
are equal.
3. Fermi level lies in
between valence and
conduction Bands.
1. It formed by adding trivalent
or pentavalent impurity to a
pure semiconductor.
2. No. of holes are more in p-
type and no. of electrons are
more in n-type.
3. Fermi level lies near valence
band in p-type and near
conduction band in n-type.

Conduction in Semiconductors
Conduction is carried out by means of
1. Drift Process.
2. Diffusion Process.

Drift process
CB
VB
• Electrons move from external circuit and in
conduction band of a semiconductor.
• Holes move in valence band of a semiconductor.
A B
V

Diffusion process
X=a
• Moving of electrons from
higher concentration
gradient to lower
concentration gradient is
known as diffusion
process.

Applications Semiconductor Materials
Semiconductors are used in almost every sector of electronics.
1. Consumer electronics: Mobile phones, laptops, games consoles, microwaves and refrigerators all operate with the use of
semiconductor components such as integrated chips, diodes and transistors. The high demand for these devices is part of the
reason there are currently such long wait times for many consumer electronic devices.

2. Embedded systems: An embedded system is a combination of computer hardware and software designed for a specific
function. Embedded systems are small computers that form part of a larger machine. They can control the device and allow user
interaction. Embedded systems that we commonly use include central heating systems, digital watches, GPS systems, fitness
trackers, televisions and engine management systems in vehicles.

3. Thermal conductivity: The thermal conductivity of the semiconductor material is one of the parameters that defines the
thermal resistance of each heat flow path. Some semiconductors have high thermal conductivity, so can be used as a cooling
agent in certain thermoelectric applications.
4. Lighting and LED displays: Some semiconductors, usually those available in liquid or amorphous form as a thin-coated film,
can produce light and are used in LEDs and OLEDs. LED LCD screens use a backlight to illuminate their pixels, while OLED's
pixels produce their own light.

5. Solar cells: Silicon is also the most commonly used semiconductor in the production of solar panel
cells.That concludes our brief guide to the applications of semiconductors. As you can see, semiconductors
are integral to the modern world and play an important role in the electronic devices we use or come into
contact with every day

Advantages and disadvantages of semiconductor materials
Advantages:
1.These are smaller in size
2. Long life compared to vacuum tubes.
3. Operated on low DC power
4. Accuracy is high compared to vacuum tubes
5. Noise is less
6. Warm up is not needed in semiconductors.
Disadvantages:
1. Cannot withstand for high power.
2. Frequency range of operation is low.
3. Produces less output power.
4. Accuracy changes with the temperature.
5. Low ambient temperature.

CHAPTER 4
INSULATING MATERIALS
Introduction to Insulating Materials:
The Electrical Insulating Material/insulating materials are the materials that inhibit heat transmission, electric
current, or noise.
The importance of the insulating materials is ever-increasing in day by day as there is an innumerable number of
types of insulators available in the market. The selection of the right type of insulating matter is very important
because the life of the equipment depends on the type of material used.

1. Large insulating resistance.
2. High dialectic strength.
3. Uniform viscosity—it gives uniform electrical and thermal properties.
4. Should be uniform throughout—it keeps the electric losses as low as possible and
electric stresses uniform under high voltage difference.
5. Least thermal expansion.
6. When exposed to arcing should be non-ignitable.
7. Should be resistance to oils or liquids, gas fumes, acids and alkalies.
8. Should have no deteriorating effect on the material, in contact with it.
9. Low dissipation factor (loss tangent).
10. High mechanical strength.
A good insulating material should possess the following characteristics:
2. Characteristics of a Good Insulating Material

11. High thermal conductivity.
12. Low permittivity.
13. High thermal strength.
14. Free from gaseous insulation to avoid discharges (for solids and gases).
15. Should be homogeneous to avoid local stress concentration.
16. Should be resistant to thermal and chemical deterioration.

3. Properties of Insulating Materials
The properties of insulating materials are enumerated and discussed as under:
1. Electrical Properties
2. Thermal Properties
3. Chemical Properties
4. Mechanical Properties.
1. Electrical Properties of Insulating Materials:
I) Insulation Resistance:It may be defined as the resistance between two conductors (or systems of
conductors) usually separated by insulating materials. It is the total resistance in respect of two parallel
paths, one through the body and other over the surface of the body.
Insulation resistance is affected by the following factors:
1. It falls with increase in temperature.
2. The resistivity of the insulator is considerably lowered in the presence of moisture.
3. It decreases with the increase in applied voltage.

a) Resistivity:
This is usually measured as insulation resistance. This term when applied to insulating materials needs
qualification to indicate whether it refers, to volume or surface.
b) Volume Resistivity:
Volume resistivity is the resistance between opposite faces of a cube of unit dimensions; it is usually
expressed in mega ohm-centimetres. The volume resistivity of most insulating materials is affected by
temperature, the resistivity decreasing with an increase of temperature, i.e., the temperature co-efficient
of resistivity is negative.
c) Surface Resistivity:
Surface resistivity is the resistance between the opposite sides of a square of unit dimension on the
surface of the materials, it is usually expressed in mega ohms per centimetre square. The surface
resistivity of any square on the surface of materials however, is independent of the size of the square
provided that the surface resistivity is uniform over the whole surface.

d) Insulation Resistance of a Cable:
In a cable useful current flows along the axis of the core but there is always present some leakage of current.
This leakage is radial i.e., at right angles to the flow of the useful current. The resistance offered to this radial
leakage of current is called “insulation resistance” of the cable. If the length of the cable is greater, the
leakage area is also greater meaning thereby that more current will leak. In other words insulation resistance
is decreased. Hence the insulation resistance is inversely proportional to the length of the cable.

ii. Dielectric Strength:
If the voltage across an insulating materials is increased slowly the way in which the current
increases depends upon the nature and condition of the material as illustrated schematically in
Fig. below.
For material I, the current
increase very slowly and
approximately linearly with
voltage until a large, sharp
increase result in what can
be described disruptive
dielectric breakdown.
In contrast, for material II the
current increases more rapidly
until current “runway” occurs. It
can be shown that the voltage
at which current “run way”
occurs depends upon the rate
at which the voltage is
increased, so that a more
definite though arbitrary, value
of dielectric breakdown may
be obtained.
The potential gradient at which
breakdown occurs is termed as
dielectric strength. It is easily
calculated for uniform fields by
dividing the breakdown voltage by
insulation thickness.

The dielectric strength of an insulating material decreases with the length of time that voltage is applied.
Moisture, contamination, elevated temperatures, heat ageing, mechanical stress, and other factors may
also markedly decrease dielectric strength to as little as 10% of the short time values at
standard laboratory condition.
Dielectric failure that occurs along the interface between a solid insulating material and air, or a liquid
insulating material is termed “surface breakdown”.
iii. Power Factor:
Power factor is a measure of the power loss in the insulation and should be low. It varies with the
temperature and usually increases with the rise in temperature of the insulation. A rapid increase indicates
danger.

The dielectric constant is the ratio of the permittivity of a substance to the permittivity of free space. It
is an expression of the extent to which a material concentrates electric flux, and is the electrical
equivalent of relative magnetic permeability.
iv. Dielectric Constant (Permittivity):
Dielectric, insulating material or a very poor conductor of electric current. When dielectrics are placed in an electric
field, practically no current flows in them because, unlike metals, they have no loosely bound, or free, electrons that may
drift through the material. Instead, electric polarization occurs. The positive charges within the dielectric are displaced
minutely in the direction of the electric field, and the negative charges are displaced minutely in the direction opposite to
the electric field. This slight separation of charge, or polarization, reduces the electric field within the dielectric.
A dielectric material is a poor conductor of electricity but an efficient supporter of electrostatic fields.

As the dielectric constant increases, the electric
flux density increases, if all other factors remain
unchanged. This enables objects of a given size,
such as sets of metal plates, to hold their electric
charge for long periods of time, and/or to hold
large quantities of charge. Materials with high
dielectric constants are useful in the manufacture
of high-value capacitors.

V. Dielectric Loss:
The dielectric losses occur in all solid and liquid dielectrics due to:
I) A conduction current: The conduction current is due to imperfect insulating qualities of the dielectric
and is calculated by the application of ohm’s law- it is in phase with the voltage and results in a power
(I²R) loss in the material which is dissipated as heat.
(ii) Hysteresis: Dielectric hysteresis is defined as the lagging of the electric flux behind the electric force
producing it so that under varying electric forces a dissipation of energy occurs, the energy loss due to
this cause being called the dielectric hysteresis loss.
The dielectric loss is affected by the following factors:
(i) Presence of humidity … it increase the loss
(ii) Voltage increase … it causes high dielectric loss
(Hi) Temperature rise … it normally increases the loss
(iv) Frequency of applied voltage … the loss increases proportionally with the frequency of applied voltage.

2. Thermal Properties of Insulating Materials:
i. Specific Heat & Thermal Conductivity:
Thermal conductivity describes the ability of a material to conduct heat, and the specific heat capacity
tells how much heat energy is absorbed or released depending on the temperature difference and
mass.
ii. Thermal Plasticity:
Pressure on the wires of a wound coil varies under operating conditions because of the expansion and
contraction of the parts caused by variations in temperature.
iii. Ignitability:
Insulating materials exposed to arcing should be non-ignitable. In case they are ignitable, they should
be self-extinguishing, resistant to cracking or carbonisation of the material.
iv. Softening Point:T he softening point is the temperature at which a material softens beyond some
arbitrary softness.The softening point of solid insulating material should be above the temperature
occurring in practice.

v. Heat Ageing:
Ageing is, in effect, the wearing out of an insulating material by reducing its resistance to mechanical injury.
It increase rapidly with temperature, approximately doubling for each increase of 10°C to 16°C, depending
upon the material.
vi. Thermal Expansion:
Thermal expansion is important because of the mechanical effects caused by thermal expansion due to
temperature changes. In insulating materials it should be very small.
3. Chemical Properties of Insulating Materials:
i. Resistance to External Chemical Effect
Insulating materials should be resistant to oils or liquids, gas fumes, acids and alkalies. The materials should not undergo
oxidation and hydrolysis even under adverse conditions.
ii. Resistance to Chemicals in Soils
Cables laid in the soil can deteriorate by the action of chemicals in soils. The suitability of insulating
materials for such conditions can be decided by a long experience.
iii. Effect of Water
Water directly lowers electrical properties, such as electrical resistance and dielectric strength.

4. Mechanical Properties of Insulating Materials
i. Density
ii. Viscosity
iii. Moisture Absorption
iv. Hardness of Surface
v. Surface Tension
vi. Uniformity

CHAPTER 5
ELECTRIC COMPONENTS AND MATERIALS
1. Introduction
2. Resistors
3. Capacitors
4. Inductors
5. Electric component testing

Electronics Components
Electronic components are basic discrete devices in any electronic system to use in electronics otherwise different associated fields. These
components are basic elements that are used to design electrical and electronic circuits. These components have a minimum of two
terminals which are used to connect to the circuit. The classification of electronic components can be done based on applications like
active, passive, and electromechanical.
In designing an electronic circuit following are taken into consideration:
 Basic electronic components: capacitors, resistors, diodes, transistors, etc.
 Power sources: Signal generators and DC power supplies.
 Measurement and analysis instruments: Cathode Ray Oscilloscope (CRO), multimeters, etc.
Passive components: cannot amplify a signal, and they do not produce mechanical motion.The most common passive electronic
components are resistors, capacitors, and inductors.
Active components can amplify a signal. The most emblematic active components are called transistors. A bipolar-junction transistor
(BJT) functions like a current-controlled current source, and a metal oxide semiconductor field-effect transistor (MOSFET)
functions like a voltage-controlled current source.
Electromechanical components convert electrical energy into mechanical motion, convert mechanical motion into electrical energy, or
facilitate electrical interconnection. The most familiar electromechanical component is the electric motor. Though the functional details of
motors vary widely, almost all of them have the same fundamental purpose: to convert electrical energy into mechanical energy in the
form of rotational motion.
Introduction

Bells, Alarms, and Horns.
Loudspeakers.
Microphones.
Geophones.
Hydrophones.
Telegraph Systems.
Telephones.
Vibrators.
Electromechanical components

Resistors
• The first use is to limit the flow of current in a circuit.
I = E / R
I = 15 V / 30 Ω
I = 0.5 A
A resistor is an electrical component that limits or regulates the flow of
electrical current in an electronic circuit. Resistors can also be used to
provide a specific voltage for an active device such as a transistor. Resistors
are commonly used to perform two functions in a circuit.

• The second use is to produce a voltage divider.
A to B = 1.5 V
A to C = 7.5 V
A to D = 17.5 V
B to C = 6 V
B to D = 16 V
C to D = 10 V

Resistor
• A component with 2 leads (connections)
• Its function in a circuit is to control the electric current flow
through the circuit
• The greater the resistance value, the less will be the
current flow
• Resistor value is measured in Ohms (Ω)
• Sometimes in a circuit the symbol for Ohms is not shown:
• 10 Ω may be written as 10R
• 0.1 Ω may be written as 0R1
• 1000 Ω may be written as 1k (1 kilo Ohms)
• The value of the resistor is read using a colour coding
scheme
Appearance
Schematic Symbol

The resistor color code can be used to determine the resistor’s ohmic
value and tolerance.

Resistor Colour Coding:
Resistance and tolerance colour bands on a resistor.

Resistance and tolerance colour code for resistors.
Resistor Colour Code
1st Band 2nd Band 3rd Band 4th Band
Band Colour
1st Digit 2nd Digit Multiplier Tolerance
Black 0 1
Brown 1 1 10
Red 2 2 100
Orange 3 3 1 000
Yellow 4 4 10 000
Green 5 5 100 000
Blue 6 6 1 000 000
Violet 7 7 10 000 000
Grey 8 8 100 000 000
White 9 9 1 000 000 000
Gold 0.1 ± 5%
Silver 0.01 ± 10%
No tolerance band ± 20%

Example a) Determine the nominal value and tolerance for the
resistor below.
b) What is the minimum resistance value this resistor
can actually have?
c) What is the maximum resistance value this resistor
can actually have?
Solution:
___ ___  10    ____ %
Resistor nominal value = 39105
= 3,900,000
= 3.9M.
Orange =3
3
White =9
9
Green =5
5
Silver = 10%
10
Tolerance = 10%

Solution: continued
 Minimum resistance value:
nominal value – nominal value * tolerance:










M
M
M
M
M
51
.
3
39
.
0
9
.
3
1
.
0
*
9
.
3
9
.
3
 Maximum resistance value:
nominal value + nominal value * tolerance:










M
M
M
M
M
29
.
4
39
.
0
9
.
3
1
.
0
*
9
.
3
9
.
3

Types of Resistors
Resistors are made in many forms but all belong in either of two groups:
Fixed resistors – are made of metal films, high-resistance wire or
carbon composition.
Variable resistors – have a terminal resistance that can be varied by
turning a dial, knob, screw, or anything else appropriate for the
application.

Fixed resistors have only one ohmic value, which cannot be changed or
adjusted. One type of fixed resistor is the composition carbon resistor.

Carbon resistors are very popular for most applications because
they are inexpensive and readily available in standard sizes and
wattages.
½ Watt 1 Watt 2 Watt

Metal film resistors are another type of fixed resistor. These resistors are
superior to carbon resistors because their ohmic value does not change
with age and they have improved tolerance.

Wire-wound resistors are fixed resistors that are made by winding a piece
of resistive wire around a ceramic core. These are used when a high
power rating is required.
A 10 , 10 W wire-wound resistor

Variable resistors can change their value over a specific range. A
potentiometer is a variable resistor with three terminals. A rheostat has
only two terminals.
A potentiometer
A rheostat.

Exceeding the power rating causes damage to a resistor.
The of a resistor is the specification given with a resistor that serves to tell the maximum
amount of power that the resistor can withstand.
Thus, if a resistor has a power rating of ¼ Watts, ¼ Watts is the maximum amount of
power that should be fed into the resistor.
Resistor power rating

Schematic symbols are used to represent various types of
fixed resistors.

Review:
1. Resistors are used in two main applications: as voltage dividers and to
limit the flow of current in a circuit.
2. The value of fixed resistors cannot be changed.
3. There are several types of fixed resistors such as composition carbon,
metal film, and wire-wound.
4. Carbon resistors change their resistance with age or if overheated.
5. Metal film resistors never change their value, but are more expensive than
carbon resistors.
6. The advantage of wire-wound resistors is their high power ratings.

Review:
7. Resistors often have bands of color to indicate their resistance value and
tolerance.
8. Resistors are produced in standard values. The number of values between 0
and 100 Ω is determined by the tolerance.
9. Variable resistors can change their value within the limit of their full value.
10. A potentiometer is a variable resistor used as a voltage divider.

The Capacitor
Capacitors are one of the fundamental passive components. In its most basic form, it
is composed of two plates separated by a dielectric. The ability to store charge is the
definition of capacitance.
Dielectric
Conductors

Dielectric
Plates
Leads
Electrons
B
A




+
+
+
+


+
+
+
+

Initially uncharged
+ 
B
A
VS
+
+
+
+
+
+
+
+
+
+
+











Fully charged
B
A
VS

+

+

+

+

+

+

+

+

+

+

+
Source removed
The charging process…
A capacitor with stored charge can act as a temporary battery.

Capacitance is the ratio of charge to voltage
Q
C
V

Rearranging, the amount of charge on a capacitor is determined by the size of the
capacitor (C) and the voltage (V).
Q CV

If a 22mF capacitor is connected to a 10 V source, the charge is
Capacitance
220 mC

An analogy:
Imagine you store rubber bands in a bottle that is
nearly full.
You could store more rubber bands (like charge
or Q) in a bigger bottle (capacitance or C) or if
you push them in with more force (voltage or V).
Thus,
Q CV


A capacitor stores energy in the form of an electric field that is established by
the opposite charges on the two plates. The energy of a charged capacitor is
given by the equation
2
2
1
CV
W 
where
W = the energy in joules
C = the capacitance in farads
V = the voltage in volts

The capacitance of a capacitor depends on three physical
characteristics.
12
8.85 10 F/m r A
C
d

  
   
 
C is directly proportional to
and the plate area.
the relative dielectric constant
C is inversely proportional to
the distance between the plates

12
8.85 10 F/m r A
C
d

  
   
 
Find the capacitance of a 4.0 cm diameter sensor immersed in oil if the
plates are separated by 0.25 mm.
The plate area is
The distance between the plates is
  
3 2
12
3
4.0 1.26 10 m
8.85 10 F/m
0.25 10 m
C



 

 
  
 

 
178 pF
 
2 2 3 2
π 0.02 m 1.26 10 m
A r  
   

Voltage and current are always 90o out of phase. For this reason, no true
power is dissipated by a capacitor, because stored energy is returned to the
circuit.
The rate at which a capacitor stores or returns energy is called reactive
power. The unit for reactive power is the VAR (volt-ampere reactive).
Energy is stored by the capacitor during a portion of the ac cycle and
returned to the source during another portion of the cycle.
Power in a capacitor

Capacitor types
Mica
Mica
Foil
Foil
Mica
Foil
Foil
Mica
Foil
Mica capacitors are small with high working voltage. The working voltage is the
voltage limit that cannot be exceeded.

Ceramic disk
Solder
Lead wire soldered
to silver electrode
Ceramic
dielectric
Dipped phenolic coating
Silv er electrodes deposited on
top and bottom of ceramic disk
Ceramic disks are small nonpolarized capacitors They have
relatively high capacitance due to high er.

Electrolytic (two types)
Symbol for any electrolytic capacitor
Al electrolytic
+
_
Ta electrolytic
Electrolytic capacitors have very high capacitance but they are not as precise as
other types and tend to have more leakage current. Electrolytic types are
polarized.

Variable
Variable capacitors typically have small capacitance values and are
usually adjusted manually.
A solid-state device that is used as a variable capacitor is the varactor
diode; it is adjusted with an electrical signal. Symbols for the capacitor: (a) fixed;
(b) variable.

Capacitor labeling
Capacitors use several labeling methods. Small capacitors values are frequently
stamped on them such as .001 or .01, which have units of microfarads.
+
+
+
+
V
TT
VT
T
4
7
M
F
.022
Electrolytic capacitors have larger values, so are read as mF. The unit is usually
stamped as mF, but some older ones may be shown as MF or MMF (MMF is the same
as pf (pico-farads)).

A label such as 103 or 104 is read as 10x103 (10,000 pF) or 10x104 (100,000
pF) respectively. (Third digit is the multiplier.)
When values are marked as 330 or 6800, the units are picofarads.
What is the value of each capacitor? Both are 2200 pF.
222 2200

The ferromagnetic materials are those
substances which exhibit strong magnetism in
the same direction of the field, when a
magnetic field is applied to it.

Or Eddy currents are loops of electrical current induced within conductors by a
changing magnetic field in the conductor according to Faraday’s law of
induction. Eddy currents flow in closed loops within conductors, in planes
perpendicular to the magnetic field.

A choke, also known as an
inductor, is used to block higher-
frequency while passing direct
current (DC) and lower-
frequencies of alternating
current (AC) in an electrical
circuit.

VARIABLE INDUCTORS
Variable inductor products are coil products that allow the inductance to be easily
varied by changing the position of the ferrite core in a threaded structure.
The interior is covered by a metal case that is magnetically shielded, while a resin
molded structure protects the windings with a high degree of reliability.

CHAPTER 6
MAGNETIC MATERIALS
1. Introduction
2. Terms associated with magnetic materials
3. Clasification of magnetic materials
4. Properties of magnetic materials
5. Magneto striction
6. Application

Introduction
Magnet: a device that attracts iron and produces a magnetic field. So that
magnetic materials are materials which get easily magnetized in a magnetic field.
Or Magnetic Materials are those materials in which a state of magnetization can
be induced.
• Many of our modern technological devices relay on magnetism and magnetic
materials.
Examples: Power generators, transformers, electric motors, radio, television,
telephones, computers & components of sound & video reproduction systems.

i.e. H=
B
ampere m
1
Magnetic dipole: The two equal and opposite magnetic poles are
separated by a small distance.
Magnetic dipole moment: The strength of that tiny magnet, the
magnetic dipole moment m, is given by m = NIA, giving the units
Ampere meter square. The magnetic dipole moment is a vector quantity and its
direction is given by the right-hand thumb rule.
magnetic flux density (B): The magnetic flux density or magnetic induction is the
number of lines of force passing through a unit area of material, B. The unit of
magnetic induction is the tesla (T).
Magnetic field Intensity (H):
Ratio between the magnetic induction and the permeability of the medium
Terms associated with magnetic materials

Magnetic Permeability (µ): Ratio of the magnetic induction to the applied magnetic field intensity
Magnetic Susceptibility (χ): Ratio between the intensity of magnetization to the applied magnetic
field intensity
Intensity of Magnetization(I or M) :
The process of converting a non magnetic material into a magnetic material.Intensity of Magnetization represents the extent
to which a specimen is magnetised when placed in a magnetising field. Or in other words the intensity of magnetisation is
defined as the magnetic dipole moment developed per unit volume when a magnetic material is subjected to magnetising
field.
=
B
H
henry m
1
=
I
H
The relative permeability
r =
0
or r =
B
0 H

Clasification of magnetic materials
Magnetic materials are classified into two categories,
1. Without permanent magnetic moments:
i) Diamagnetic materials
2. With permanent magnetic moments:
i) Paramagnetic materials
ii) Ferromagnetic materials
iii) Anti-Ferromagnetic materials
iv) Ferri magnetic materials

Permanent Dipoles
Alignment of
dipoles
Direction of
dipoles
Magnitudes of
dipoles
Dia magnetic
materials
Para, Ferro, Anti ferro,
Ferri magnetic materials
Para
Uniform
Ferro, Anti ferro, Ferri
Ferro Anti ferro, Ferri
Anti ferro
Ferri

Diamagnetic Materials
• It is a weak form of magnetism
• Diamagnetism is because of orbital magnetic moment.
• No permanent dipoles are present so net magnetic moment is zero.
• Persists only when external field is applied.
• The number of orientations of electronic orbits is such that the vector
sum of the magnetic moments is zero.
• Dipoles are induced by change in orbital motion of electrons due to
applied magnetic field.

No Applied
Magnetic Field (H = 0)
Applied
Magnetic Field (H)
none
opposing

• External field will cause a rotation action on the individual
electronic orbits.
• The external magnetic field produces induced magnetic
moment which is due to orbital magnetic moment.
• Induced magnetic moment is always in opposite direction of
the applied magnetic field.
• So magnetic induction in the specimen decreases.
• Magnetic susceptibility is small and negative.
• Repels magnetic lines of force.

• Diamagnetic susceptibility is independent of temperature and
applied magnetic field strength.
• Susceptibility is of the order of -10-5.
• Relative permeability is less than one.
• It is present in all materials, but since it is so weak it can be
observed only when other types of magnetism are totally
absent.
• Examples: Bi, Zn, gold, H2O, alkali earth elements (Be, Mg,
Ca, Sr), superconducting elements in superconducting state.

Paramagnetic Materials
• Possess permanent dipoles.
• If the orbital's are not completely filled or spins not balanced,
an overall small magnetic moment may exist.
• i.e. paramagnetism is because of orbital and spin magnetic
moments of the electron.
• In the absence of external magnetic field
• all dipoles are randomly oriented
• so net magnetic moment is zero.
• Spin alignment is random.
• The magnetic dipoles do not interact

No Applied
Applied
Magnetic Field (H)
random
aligned

• In presence of magnetic field the
• material gets feebly magnetized i.e. the material allows
few magnetic lines of force to pass through it.
• Relative permeability µr >1 (barely, ≈ 1.00001 to 1.01).
• The orientation of magnetic dipoles depends on temperature
and applied field.
• Susceptibility is independent of applied mag. field & depends
on temperature
• C is Curie constant

• With increase in temperature susceptibility decreases.
• Susceptibility is small and positive.
• These materials are used in lasers.
• Paramagnetic property of oxygen is used in NMR technique
for medical diagnose.
• The susceptibility range from 10-5 to 10-2.
• Examples: alkali metals (Li, Na, K, Rb), transition metals, Al,
Pt, Mn, Cr etc.

• Permanent dipoles are present so possess net magnetic
moment
• Origin for magnetism in Ferro mag. Materials is due to Spin
magnetic moment of electrons.
• Material shows magnetic properties even in the absence of
external magnetic field.
• Possess spontaneous magnetization.
• Spontaneous magnetization is because of interaction between
dipoles called EXCHANGE COUPLING.
Ferromagnetic Materials

aligned
aligned
No Applied
Applied
Magnetic Field (H)

• When placed in external mag. field it strongly attracts magnetic
lines of force.
• All spins are aligned parallel & in same direction.
• Susceptibility is large and positive, it is given by Curie Weiss
Law
• C is Curie constant & θ is Curie temperature.
• When temp is greater than curie temp then the material gets
converted in to paramagnetic.
• Material gets divided into small regions called domains.
• They possess the property of HYSTERESIS.
• Examples: Fe, Co, Ni.

Even when H = 0, the dipoles
tend to strongly align over
small patches.
When H is applied, the domains
align to produce a large net
magnetization.

 The temperature above (Tc) which ferromagnetic material become
paramagnetic.
 Below the Curie temperature, the ferromagnetic is ordered and
above it, disordered.
 The saturation magnetization goes to zero at the Curie
temperature.
Curie Temperature

• The spin alignment is in antiparallel manner.
• So net magnetic moment is zero.
• Susceptibility depends on temperature.
• Susceptibility is small and positive.
• Initially susceptibility increases with increase in temperature
and beyond Neel temperature the susceptibility decreases with
temperature.
• At Neel temperature susceptibility is maximum.
• Examples: FeO, MnO, Cr2O3 and salts of transition elements.
Antiferro magnetic Material

Ferrimagnetic
Materials
Cubic Ferrites
MFe2O4
Hexagonal
Ferrites
AB12O19
Garnets
M3Fe5O12
Ferri-magnetic Materials
Classification of Ferri-magnetic Materials

• Special type of ferro and antiferromagnetic material.
• Generally oxides in nature.
• Ionic in nature
• Ceramic in nature so high resistivity (insulators)
• The spin alignment is antiparallel but different magnitude.
• So they possess net magnetic moment.
• Also called ferrites.
• General form MFe2O4 where M is a divalent metal ion.
• Susceptibility is very large and positive.
• Examples: ferrous ferrite, nickle ferrite

• Magnetostriction is a property of ferromagnetic materials which causes them
to expand or contract in response to a magnetic field. This effect allows
magnetostrictive materials to convert electromagnetic energy into mechanical
energy. As a magnetic field is applied to the material, its molecular dipoles
and magnetic field boundaries rotate to align with the field. This causes the
material to strain and elongate. Energy produced in this effect is called
Magnetostriction Energy.
• The deformation is different along different crystal directions & the change in
dimension depends on nature of the material.
Magnetostriction

Used as transformer cores
Used as induction cores, antennas for medium and long wave broad casting,
electronic tuning, auto frequency control, FM, switching etc.
Magnetic materials applications
 Since ferrites have a domains & hysteresis loop they are used as memory
elements for rapid storage and retrieval of digital information by
switching the direction of magnetization in very small toroidal cores.
 Garnets (Y3Fe5O12) are useful in microwave applications.
 Magnetic recording uses ferrite material in powder form.
 Ferrites can be used as magnets.
Ferrites Being Ferro-magnetic
1. Ferrite applications

2) Magnetic Storage
Reading Process
Writing Process
Storage of data( Tapes, Floppy and Magnetic
Disc Drives)
3) Transformer
4) Motors

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