2. electrical
There are three primary electrical parameters: the volt,
the ampere and the ohm. Voltage is the pressure from an
electrical circuit's power source that pushes charged
electrons (current) through a conducting loop, enabling
them to do work such as illuminating a light. In brief,
voltage = pressure, and it is measured in volts (V). An
ampere is a unit of measure of the rate of electron flow or
current in an electrical conductor. One ampere of current
represents one coulomb of electrical charge (6.24 x 1018
charge carriers) moving past a specific point in one
second. The SI derived unit used to measure the electrical
resistance of a material or an electrical device. One ohm
is equal to the resistance of a conductor through which a
current of one ampere flows when a potential difference
of one volt is applied to it
3. electrical
Electrical properties are their ability to conduct
electrical current. Various electrical properties are
resistivity, Electrical conductivity, temperature
coefficient of resistance, dielectric strength and
thermoelectricity. The resistivity of a material is a
measure of how strongly a material opposes the
flow of electrical current. The unit of resistivity in SI
units is the ohm-meter (Ω⋅ Electrical conductivity is
nothing but the measure of the capability of the
material to pass the flow of electric current.
Electrical conductivity differs from one material to
another depending on the ability to let the electricity
flow through them.
4. electrical
Temperature coefficient of resistance (TCR) is the
calculation of a relative change of resistance per
degree of temperature change. The dielectric
strength of a material is a measure of the electrical
strength of an insulator. It is defined as the
maximum voltage required to produce a dielectric
breakdown through the material and is expressed in
terms of Volts per unit thickness. Thermoelectricity is
the direct and thermodynamically reversible
conversion of heat to electricity and vice versa.
5. magnetic
Magnetic lines of force form a complete loop and
are continuous. The opposite poles of magnets
attract each other whereas like poles repel one
another. The magnetic lines of force are denser at
the poles of a magnet. Parallel magnetic lines of
force that travel in opposite directions cancel each
other.
Magnetic properties
1. Diamagnetic They are weakly repelled by the
magnetic fields
2. Paramagnetic They are weakly attracted by the
magnetic fields.
6. thermal
The responses of solids against the thermal effects
are termed as thermal properties of materials.
Proper selection of materials for favourable low and
high temperature applications requires knowledge
of their thermal properties.
7. Many engineering solids when exposed to heat experiences an increase
in temperature i.e. it absorbs heat energy. This property of a material i.e.
material’s ability to absorb heat energy is called its heat capacity, C. It is
defined as the energy required to change a material’s temperature by
one degree.
Heat energy absorption of a (solid, liquid or gaseous) material exists in
mode of thermal energy vibration of constituent atoms or molecules
apart from the other mechanical heat absorption such as electronic
contribution. With increase of energy, atoms vibrate at higher
frequencies.
HEAT CAPACITY
8. After heat absorption, atoms started vibrating and having larger atomic
radius, leads to increase in materials dimensions. The phenomenon is
called thermal expansion.
THERMAL EXPANSION
THERMAL CONDUCTIVITY
The ability of a material to transport heat energy from high temperature
region to low temperature region is defined as thermal conductivity.
9. After heat absorption, atoms started vibrating and having larger atomic
radius, leads to increase in materials dimensions. The phenomenon is
called thermal expansion.
The distribution of residual stresses is not always symmetrical within the
material. Uneven cooling is a cause of such unbalanced stresses, it
happens because when one surface of a material is cooled more rapidly
than the other, the rapidly cooled surface generates compression
whereas tension is developed on other surface. Such asymmetry
produces ‘warpage’ and the material develops convexity towards
rapidly cooled surface.
THERMAL STRESS
10. b. Joints of two railroad rails,
e. Refractory bricks in
metallic furnaces and ovens,
c. Jacketed thick cylinders
that are shrink fitted,
f.Outer skins of
rockets and missiles
d. Bimetallic strips in
thermostatic controls,
a. Welded construction of structures
and the pressure vessels,
12. The residual stresses produced within plastic materials may be
relieved partially by warpage, but this is not so in case of non-plastic
materials. In them, the dimensional changes cannot relieve the
stresses, and the stresses in excess of elastic limit produce thermal
cracking. This is called spalling. This is a very common phenomenon
in glassware.
SPARLLING OT THERMAL
CRACKLING
13. Behaviour of a material under repeated heating and cooling is known
as thermal fatigue. Due to thermal fatigue, thermal stresses of
fluctuating nature are produced in the material which may eventually
cause its thermal fatigue failure. The ability of a material to withstand
such failure is called thermal fatigue resistance.
THERMAL FATIGUE
14. A situation in the material, when there is a severe and sudden
temperature change, is known as thermal shock. The capability of a
material to withstand this effects of such drastic change is called
thermal shock resistance.
THERMAL SHOCK
16. chemical
A chemical property is a characteristic or behavior of a substance
that may be observed when it undergoes a chemical change or
reaction. Chemical properties are seen either during or following a
reaction since the arrangement of atoms within a sample must be
disrupted for the property to be investigated. This is different from a
physical property, which is a characteristic that may be observed
and measured without changing the chemical identity of a
specimen.
17. example of chemical
properties
1 toxicity
2 reactivity
3
types of chemical bonds
form
4 oxidation states
5 flammability
6 heat of combustion
18. a chemical change must occur for a chemical property to be
observed and measured. For example, iron oxidizes and becomes
rust. Rusting is not a property that can be described based on
analysis of the pure element.
REMEMBER
19. Chemical properties are of great interest to materials science. These
characteristics help scientists classify samples, identify unknown
materials, and purify substances. Knowing the properties helps
chemists make predictions about the type of reactions to expect.
Because chemical properties are not readily apparent, they are
included in labels for chemical containers. Hazard labels based on
chemical properties should be affixed to containers, while full
documentation should be maintained for easy reference.
USES OF CHEMICAL PROPERTIES
20. optical
Optical property deals with the response of a material
against exposure to electromagnetic radiations, especially
to visible light. When light falls on a material, several
processes such as reflection, refraction, absorption,
scattering etc.
21. When light photons are transmitted through
a material, they causes polarization of the
electrons in the material and by interacting
with the polarized materials, photons lose
some of their energy. As a result of this, the
speed of light is reduced and the beam of
light changes direction.
REFRACTION
REFRLECTION
When a beam of photons strikes a
material, some of the light is scattered
at the interface between that we
media even if both are transparent.
Reflectivity, R, is a measure of fraction
of incident light which is reflected at
the interface
22. ABSORBTION
When a light beam is striked on a material surface,
portion of the incident beam that is not reflected by
the material is either absorbed or transmitted through
the material. The fraction of beam that is absorbed is
related to the thickness of the materials and the
manner in which the photons interact with the
material’s structure
23. Here photon interacts with the electron orbiting around an atom and
is deflected without any change in photon energy. This is more vital
for high atomic number atoms and low photon energies. Ex. Blue
colour in the sunlight gets scattered more than other colors in the
visible spectrum and thus making sky look blue.
RAYLEIGH SCATTERING
TYNDALL EFFECT
Here scattering occur form particles much larger
than the wavelength of light Ex. cloud look white
COMTOPN SCATTERING
In this incident photon knocks out an electron from
the atom losing some of its energy during the
process.
24. The fraction of beam that is not reflected or absorbed is transmitted
through the material. Thus the fraction of light that is transmitted
through a transparent material depends on the losses incurred by
absorption and reflection. Thus, R + A + T = 1
where R = reflectivity,
TRANSMISSION
25. When a material is heated electrons are excited to higher energy
levels generally in the outer energy levels where the electrons are less
strongly bound to the nucleus. These excited electrons, upon returning
back to the ground state, release photons in process termed as
thermal emission.
By measuring the intensity of a narrow band of the emitted
wavelengths with a pyrometer, material’s temperature can be
estimated.
THERMAL EMISSION
26. When a material is heated electrons are excited to
higher energy levels generally in the outer energy
levels where the electrons are less strongly bound
to the nucleus. These excited electrons, upon
returning back to the ground state, release
photons in process termed as thermal emission.
By measuring the intensity of a narrow band of the
emitted wavelengths with a pyrometer, material’s
temperature can be estimated.
ELECTRO-OPTIC
EFFECT
BRIGHTNESS
Power emitted by a source per unit area per unit
solid angle.
27. Phenomenon in which the ejection
of electrons from a metal surface
takes place, when the metal surface
is illuminated by light or any other
radiation of suitable frequency (or
wavelength). Several devices such
as phototube, solar cell, fire alarm
etc. work on this effect (principle).
PHOTO ELECTREC
EFFECT
PHOTO
EMESSIVITY
Phenomenon of emission of
electrons from a metal cathode,
when exposed to light or any other
radiations.
28. These materials may be transparent, translucent,
or opaque. Therefore, they exhibit different optical
properties such as reflection, refraction, absorption
and transmission. The phenomenon of refraction is
more dominant in them.
ii. The non-metals which are transparent are generally
coloured due to light absorption and remission in the
visible region by them. Absorption of light occurs due
to: Electronic polarization.
optical properties of non-
metals
29. i. In metals, the valence band is partially filled and so there are large number of
quasi continuous vacant energy levels available within the valence band. When
light is incident on metals the valence electrons absorb all frequencies of visible
light and get excited to vacant states inside the valence band (intra-band
transitions). This result in the opacity of metals.
ii. The total absorption of light by the metal surface is within a very thin outer layer
of less than 0.1 jam. The excited electrons return back to lower energy states
thereby causing emission of radiation from the surface of the metal in the form of
visible light of the same wavelength. This emitted light which appears as the
reflected light is the cause of the lustrous appearance of metals.
optical properties of metals
30. Luminescence is the property by which a material
emits the light.
luminescence
different types of luminescence
1.photo- luminescence
It is the phenomenon of emission of light from a semiconductor on
account of recombination of excited electron-hole pair (EHP).
Here one photon is emitted from each photon absorbed.
Recombination in semiconductors takes place at varying rates; fast and slo
a.flourescence
It is a fast process property of material in which
the emission of photon stops in about 10–8s after
the excitation is removed.
Example: (i) Glass surface coated with tungstates
or silicates such as in fluorescent lamps.
(ii) Television screen coated with sulphides,
oxides, tungstates etc
b.phosphorescence
continues for a longer durSlow process property
of material in which the emission of photon ation,
lasting for seconds and minutes after removal of
excitation.
31. 2.electro luminescence
I.This effect can be created by introducing the electric current into a semiconductor. The
electrical current can be used in different ways to generate the photon emission from
semiconductors. One such way is ‘injection’.The name of the process is injection electro-
luminescence which is use in making light-emitting diodes (LEDs).n them the minority carriers
are injected by electric current, into the regions of a crystal where they can recombine with
majority carriers. It results in emission of recombination radiation.The effect of electro-
luminescence can be found in devices incorporating the phosphor powder (such as of ZnS) in a
plastic binder.This phosphor gives-off the light when an alternating current (a.c.) filed is
applied on it. Such device is known as ‘electro-luminescence cell’, which is used as lighting
panel.Destriau effect- The emission of photons in certain phosphors occurs when they are
subjected to alternating electric field, was observed for the first time by Destriau. Hence this
phenomenon is known as ‘Destriau effect’.
32. i. Insulators have completely filled valence band and so like as
in semiconductors, no intra-band transitions can occur.
ii. The energy gap in insulators are greater than 5 eV and so no
inter-band transition can occur in the visible range of
radiation.
iii. Absorption occurs only for the ultraviolent radiation.
Insulators are transparent from infra-red up to the ultra-violet
radiation.
Examples:
a. Perfect diamond crystal
b. Fused quartz
c. Window glass
optical properties of
insulators
33. iv. Above materials are opaque because the incident
radiation gets scattered in all direction by the small
particles present in these materials.
v. Due to this, there cannot be perfect transmission.
Part of the radiation is diffusely transmitted and part is
diffusely reflected. This makes the materials appear
opaque.
vi. If the particle size is of the order of the wavelength of
visible radiation, there will be maximum scattering.
vii. For some applications, such particles are
deliberately introduced in dielectrics to make them
opaque.
non-transparent insulators
examples of non transparent
insulators
a. Enamels,
b. Porcelains,
c. Opal glass etc.
34. i. Ionic crystals are insulators. The energy gap in these crystal are in the range of
5-8 eV. The electrons cannot absorb photons in the visible radiation and get
excited to the conduction band. So the complete range of visible radiation is
transmitted by ionic crystals and they are transparent.
ii. The absorption properties of ionic crystals change drastically if point defects
such as lattice vacancy or Schottky defects are present in them. Because of this
defect materials are found to be colored.
iii. Another method by which the optical absorption in ionic crystals can be
changed is by adding impurities.
iv. Lower yield strength,
v. Polymorphic transformations
vi. Decrease in hardness etc.
OPTICAL ABSOPTION IN IONIC CRYSTAL
35. Mechanical
The mechanical properties of a material are those which affect the mechanical
strength and ability of a material to be molded in suitable shape. Some of the
typical mechanical properties of a material include:
• Strength
• Toughness
• Hardness
• Hardenability
• Brittleness
• Malleability
• Ductility
• Creep and Slip
• Resilience
• Fatigue
Mechanical
examples of non transparent
insulators
a. Enamels,
b. Porcelains,
c. Opal glass etc.
