WELCOME [] · 2020. 3. 3. · • A molecule scatters light because it is polarizable. Hence the...
Transcript of WELCOME [] · 2020. 3. 3. · • A molecule scatters light because it is polarizable. Hence the...
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WELCOME
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Atomic and molecular Physics
- study of the spectroscopy
T.Y. B.Sc- 2018-19T.Y. B.Sc- 2018-19
Prof. Ghule N.B.
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SPECTROSCOPY
• Spectroscopy is that branch of
science which deals with the study of
interaction of electromagnetic interaction of electromagnetic
radiations with matter
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Raman spectra
• This is based on scattering of radiation and not on the absorption of radiation by the sample. by the sample.
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RAMAN SPECTRA
GENERAL INTRODUCTION
• It is a type of spectroscopy which deals not with the absorption of electromagnetic radiation but deals with the scattering of light by the molecules. When a substance which may be gaseous, liquid or even solid is irradiated with monochromatic light of a definite is irradiated with monochromatic light of a definite frequency v, a small fraction of the light is scattered. Rayleigh found that if the scattered light is observed at right angles to the direction of the incident light, the scattered light is found to have the same frequency as that of the incident light. This type of scattering is called Rayleigh scattering.
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• When a substance is irradiated with
monochromatic light of a definite frequency v,
the light scattered at right angles to the
incident light contained lines not only of the
incident frequency but also of lower incident frequency but also of lower
frequency and sometimes of higher frequency
as well. The lines with lower frequency are
called Stokes' lines whereas lines with higher
frequency are called anti-Stokes' lines.
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• Raman further observed that the difference between the frequency of the incident light and that of a particular scattered line was constant depending only upon the nature of the substance being irradiated and was completely independent of the frequency of the incident light. If vi is the frequency of the incident light and vs' that of particular incident light and vs' that of particular scattered line, the difference v = vi - vs is called Raman frequency or Raman shift.
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EXPLANATION FOR OBSERVING
RAYLEIGH LINE
AND RAMAN LINES
• Elastic and inelastic collisions between the
radiations and interacting molecules results in the
formation of Rayleigh and Raman lines. formation of Rayleigh and Raman lines.
• In terms of excitation of electrons
• vabs = ve Rayleigh line
• vabs > ve Stokes line
• vabs < ve Anti Stokes line
•
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POLARIZABILITY OF MOLECULES
AND RAMAN SPECTRA
• The Raman effect arises on account of the polarization
(distortion of the electron cloud) of the scattering
molecules that is caused by the electric vector of the
electromagnetic radiation. The induced dipole moment electromagnetic radiation. The induced dipole moment
depends upon the strength of the electric field E and the
nature of the molecules represented by α
• μ= αE
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• In case of atoms or spherically symmetrical
molecules (spherical rotors) such as CH4' SF6
etc same polarizability is induced whatever be
the direction of the applied electric field.
They are said to be isotropically polarizable.
Such molecules are said to be isotropic
molecules.molecules.
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• In case of all diatomic molecules
(homonuclear or heteronuclear) or non-
spherical molecules (non-spherical rotors), the
polarizability depends upon the direction of
the electric field.
• Such molecules are, therefore, said to
anisotropically polarizable.anisotropically polarizable.
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Types of molecules showing Rotational
Raman Spectra.
• A molecule scatters light because it is polarizable. Hence the gross selection rule for
a molecule to give a rotational Raman
spectrum is that the polarizability of the
molecule must be anisotropic i.e. the molecule must be anisotropic i.e. the
polarizability of the molecule must depend
upon the orientation of the molecule with
respect to the direction of the electric field.
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• Hence all diatomic molecules, linear
molecules and non-spherical molecules give
Raman spectra i.e. they are rotationally
Raman active. On the other hand, spherically
symmetric molecules such as CH4' SF6 etc. do symmetric molecules such as CH4' SF6 etc. do
not give rotational Raman spectrum i.e. they
are rotationally Raman inactive. (These
molecules are also rotationally microwave
inactive).
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PURE ROTATIONAL RAMAN SPECTRA OF
DIATOMIC MOLECULES
• The selection rules for pure rotational Raman spectra of diatomic molecules are
• ΔJ = 0 , + 2• ΔJ = 0 , + 2
•• The selection rule ΔJ = 0 corresponds to
Rayleigh scattering whereas selection rule
• ΔJ = + 2 gives rise to Raman lines as explained .
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INTENSITIES OF LINES OF THE PURE
ROTATIONAL RAMAN SPECTRA
• As explained earlier, the intensities of lines
depend upon the population of initial level
from where the molecules are excited or de-from where the molecules are excited or de-
excited to the final level. Since the population
of rotational energy levels is as shown in Fig.
therefore the intensities of the Stokes' and
anti-Stokes' lines vary in a similar manner.
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APPLICATION OF PURE ROTATIONAL
RAMAN SPECTRA
• From the pure rotational Raman spectra,
noting the separation between the lines, the
value of B can be obtained from which the
moment of inertia and the bond length of the moment of inertia and the bond length of the
diatomic molecules can be calculated
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ADVANTAGES OF RAMAN SPECTROSCOPY
OVER INFRA-RED SPECTROSCOPY
• Raman frequencies are independent of the
frequency of the incident radiation, hence by
suitable adjusting the frequency of the suitable adjusting the frequency of the
incident radiation, Raman spectra can be
obtained in the visible spectrum
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• Raman spectra can be obtained even for
molecules such as O2' N2' C12 etc. which have
no permanent dipole moment. Such a study
has not been possible by infra-red
spectroscopy.
• Raman spectra can be obtained not only for
gases but even for liquids and solids whereas
infra-red spectra for liquids and solids are
quite diffuse.
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THANK YOU THANK YOU THANK YOU THANK YOU THANK YOU THANK YOU THANK YOU THANK YOU
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Wel comeWel come
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Element of Material Science
- Introduction of Material
& Type of Material& Type of Material
T.Y. B.Sc- 2018-19
prof. Ghule N.B.
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Definition 1: A branch of science that focuses on materials; interdisciplinary field composed of physics and chemistry.
Definition 2: Relationship of material properties to its
What is material science?
Introduction
Definition 2: Relationship of material properties to its composition and structure.
What is a material scientist?
A person who uses his/her combined knowledge of
physics, chemistry and metallurgy to exploit
property-structure combinations for practical use.
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6t5ctWhat is materials ?
What do we mean when we say “materials”?
1. Metals 2. Ceramics 3. Polymers 4. Composites1. Metals
- aluminum
- copper
- steel (iron alloy)
- nickel
- titanium
2. Ceramics
- clay
- silica glass
- alumina
- quartz
3. Polymers
- polyvinyl chloride (PVC)
- Teflon
- various plastics
- glue (adhesives)
- Kevlar
semiconductors (computer chips, etc.) = ceramics, composites
nanomaterials = ceramics, metals, polymers, composites
4. Composites
- wood
- carbon fiber resins
- concrete
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wserreAtomic Structure 10-10 m
• Pertains to atom electron structure and
atomic arrangement
• Atom length scale
– Includes electron structure – atomic bonding
• ionic
• covalent
• metallic• metallic
• London dispersion forces (Van der Waals)
– Atomic ordering – long range (metals), short
range (glass)
• 7 lattices – cubic, hexagonal among most
prevalent for engineering metals and ceramics
• Different packed structures include: Gives total
of 14 different crystalline arrangements
(Bravais Lattices).
– Primitive, body-centered, face-centered
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NnNanostructureaano Structure – 10-9
m• Length scale that pertains to
clusters of atoms that make up
small particles or material
features
• Show interesting properties • Show interesting properties
because increase surface area
to volume ratio
– More atoms on surface
compared to bulk atoms
– Optical, magnetic, mechanical
and electrical properties change
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MMicrostructureicrostructure – 10-6
• Larger features composed of either nanostructured materials or
periodic arrangements of atoms known as crystals
• Features are visible with high magnification in light microscope.
– Grains, inclusions other micro-features that make up material
– These features are traditionally altered to improve material performance– These features are traditionally altered to improve material performance
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Macrostructure
• Macrostructure pertains to
collective features on collective features on
microstructure level
• Grain flow, cracks, porosity
are all examples of
macrostructure features
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ClClass of Materialsf Materials
• metals
• polymers
• ceramics
• composites• composites
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MetalsMetals• Metals consist of alkaline, alkaline earth, metalloids and
transition metals
• Metal alloys are mixtures of two or more metal and nonmetal
elements (for example, aluminum and copper, Cu-Ni alloy, steel)
• Bonding: Metallic
– No particular sharing or donating occurs. Electron cloud is formed (that is,
free electrons)free electrons)
– Strong bonds with no hybridization or directionality
• Properties:
– Electrically conductive (free electrons)
– Thermally conductive
– High strength – large capacity to carry load over x-section area (stress)
– Ductile – endure large amounts of deformation before breaking.
– Magnetic – ferromagnetism, paramagnetic
– Medium melting point
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MetalMetal Application Applications
• Electrical wire: aluminum, copper, silver
• Heat transfer fins: aluminum, silver
• Plumbing: copper
• Construction beams (bridges, sky scrapers, rebar, etc.): steel (Fe-C alloys)
• Cars: steel (Fe-C alloys)• Cars: steel (Fe-C alloys)
• Consumer goods: – soup cans
– appliances (stainless steel sheet metal)
– utensils
– tools
– Many, many, many more…
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PPolymersolymers
• Polymers consist of various hydro-carbon (organic elements) with select additives to elucidate specific properties
• Polymers are typically disordered (amorphous) strands of hydrocarbon molecules.
• Bonding: Covalent-London Dispersion Forces• Bonding: Covalent-London Dispersion Forces
• Properties: – ductile: can be stretched up to 1000% of original length
– lightweight: Low densities
– medium strength: Depending on additives
– chemical stability: inert to corrosive environments
– low melting point
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PolPolymer Applicationsymer
Applications• Car tires: vulcanized polymer (added sulfur)
• Ziploc bags
• Food storage containers
• Plumbing: polyvinyl chloride (PVC)
• Kevlar
• Aerospace and energy applications: Teflon• Aerospace and energy applications: Teflon
• Consumer goods:
– calculator casings
– TV consuls
– shoe soles
– cell phone casings
– Elmer’s Glue (adhesives)
– contact lenses
– Many, many. many more…
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zCeramicsCeramics• Consist of metal and non metal elements
• Typically a mixture of elements in the form of a chemical compound , for example Al2O3 or glass
• Three types: composites, monolithic and amorphous ceramics
• Bonding covalent – ionic– Typically covalent. In some cases highly direction covalent bonding
– Ionic in case of SiO2 glasses and slags
• Properties:• Properties:– wear resistant (hard)
– chemical stability: corrosion resistant
– high temperature strength: strength retention at very high temperatures
– high melting points
– good insulators (dielectrics)
– adhesives
– good optical properties
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CeraCeramic Applicationsmic
Applications
• Window glass: Al2O3 – SiO2 – MgO – CaO
• Aerospace, energy and automotive industry– heat shield tiles
– engine components– engine components
– reactor vessel and furnace linings
• Consumer products:– pottery
– dishes (fine china, plates, bowls)
– glassware (cups, mugs, etc.)
– eye glass lenses
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Composites• A mixture of two different materials to create a new material with
combined properties
• Types of composites:
– Particulate reinforced – discontinuous type with low aspect ratio
– Whisker/rod reinforced - discontinuous type with high aspect ratio
– Fiber reinforced - continuous type with high aspect ratio (naturally)
– Laminated composites - layered structures (surf boards, skate boards)
• Bonding: depends on type of composite (strong-covalent, medium-
solid solution, weak-tertiary phase layer)
• Properties: Depends on composites
– High melting points with improved high temperature strength:
ceramic-ceramic
– High strength and ductile with improved wear resistance: metal-
ceramic
– High strength and ductile: polymer-polymer
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C
oComposites Applicationsmposites:
Applications
• Wood: naturally occurring biological material
consists of very strong fibers imbedded in a soft
matrix
• Plywood: laminated wood for buildings• Plywood: laminated wood for buildings
• Concrete: basements, bridges, sidewalks
• Fiberglass: boats
• Carbon fiber resins: bicycle frames
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O
hOther well Known materialse well
known materials• Semiconductors – ceramics
– computer chips
– memory storage devices
– solar cells
– image screens – image screens
• Nanomaterials – ceramics, metals, polymers
– gold nanoshells
– quantum dots
– ferrofluids
– medical devices
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Thank YouThank You
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WELCOMEWELCOMEWELCOMEWELCOMEWELCOMEWELCOMEWELCOMEWELCOME
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MECHANICS
Newtons law of Motion
F.Y.B.Sc 2018-19F.Y.B.Sc 2018-19
Prof. Ghule N.B.
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Newtons of
MotionMotion
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BackgroundBackground
• Sir Isaac Newton (1643-1727) was an
English scientist and mathematician
famous for his discovery of the law of
gravity also discovered the three laws of
motion. motion.
• Today these laws are known as Newton’s
Laws of Motion and describe the motion of
all objects on the scale we experience in our
everyday lives.
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“If I have ever made any valuable discoveries, it has
been owing more to patient attention, than to any
other talent.”
-Sir Isaac Newton
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Newton’s Laws of MotionNewton’s Laws of Motion
1. An object in motion tends to stay
in motion and an object at rest tends
to stay at rest unless acted upon by
an unbalanced force.an unbalanced force.
2. Force equals mass times acceleration
(F = ma).
3. For every action there is an
equal and opposite reaction.
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Newton’s First LawNewton’s First Law
An object at rest tends to stay at rest
and an object in motion tends to stay
in motion unless acted upon by an
unbalanced force.
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What does this mean?What does this mean?
Basically, an object will “keep doing what it was doing” unless acted on by an unbalanced force.
If the object was sitting still, it will remain If the object was sitting still, it will remain stationary. If it was moving at a constant velocity, it will keep moving.
It takes force to change the motion of an object.
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FORCE
A force is a push or pull
upon an object resulting upon an object resulting
from the interaction with
another object.
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FORCE
A force is a push or pull
upon an object resulting upon an object resulting
from the interaction with
another object.
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What is meant by What is meant by unbalanced unbalanced
force?force?
If the forces on an object are equal and opposite,
they are said to be balanced, and the object
experiences no change in motion. If they are not
equal and opposite, then the forces are unbalanced
and the motion of the object changes.
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Some Examples from Real LifeSome Examples from Real Life
A soccer ball is sitting at rest. It
takes an unbalanced force of a kick
to change its motion.
Two teams are playing tug of war. They are both exerting equal force on the rope in opposite directions. This balanced force results in no change of motion.
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Newton’s First Law is also called Newton’s First Law is also called
the the Law of InertiaLaw of Inertia
Inertia: the tendency of an object to resist changes in its state of motionresist changes in its state of motion
The First Law states that all objects have inertia. The more mass an object has, the more inertia it has (and the harder it is to change its motion).
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Newton’s Second LawNewton’s Second Law
Force equals mass times acceleration.
F = ma
Acceleration: a measurement of how quickly an
object is changing speed.
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What does F = ma say?What does F = ma say?F = ma basically means that the force of an object
comes from its mass and its acceleration.
Something very massive (high mass)
that’s changing speed very slowly (low
acceleration), like a glacier, can still
Something very small (low mass) that’s changing speed very quickly (high acceleration), like a bullet, can still have a great force. Something very small changing speed very slowly will have a very weak force.
have great force.
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Newton’s Third LawNewton’s Third Law
For every action there is an equal and
opposite reaction.
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What does this mean?
For every force acting on an object, there is an equal
force acting in the opposite direction. Right now,
gravity is pulling you down in your seat, but
Newton’s Third Law says your seat is pushing up
against you with equal force. This is why you are
not moving. There is a balanced force acting on
you– gravity pulling down, your seat pushing up.you– gravity pulling down, your seat pushing up.
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What is momentum?
• the strength or force that something has when
it is moving
• Product of mass and velocity
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Newton’s Third Law and MomentumNewton’s Third Law and Momentum
“For every action there is an equal and opposite reaction.”
Momentum: a quantity defined as the Momentum: a quantity defined as the product of mass and velocity of an
object.
Momentum = mass x velocity
p=mv
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THANK YOUTHANK YOUTHANK YOUTHANK YOUTHANK YOUTHANK YOUTHANK YOUTHANK YOU
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WELCOME
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SPECTROSCOPY
• Spectroscopy is that branch of
science which deals with the study of
interaction of electromagnetic interaction of electromagnetic
radiations with matter
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Atomic and molecular Physics
- study of the spectroscopy
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SPECTROSCOPY
• Spectroscopy is that branch of
science which deals with the study of
interaction of electromagnetic interaction of electromagnetic
radiations with matter
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Raman spectra
• This is based on scattering of radiation and not on the absorption of radiation by the sample. by the sample.
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RAMAN SPECTRA
GENERAL INTRODUCTION
• It is a type of spectroscopy which deals not with the absorption of electromagnetic radiation but deals with the scattering of light by the molecules. When a substance which may be gaseous, liquid or even solid is irradiated with monochromatic light of a definite is irradiated with monochromatic light of a definite frequency v, a small fraction of the light is scattered. Rayleigh found that if the scattered light is observed at right angles to the direction of the incident light, the scattered light is found to have the same frequency as that of the incident light. This type of scattering is called Rayleigh scattering.
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• When a substance is irradiated with
monochromatic light of a definite frequency v,
the light scattered at right angles to the
incident light contained lines not only of the
incident frequency but also of lower incident frequency but also of lower
frequency and sometimes of higher frequency
as well. The lines with lower frequency are
called Stokes' lines whereas lines with higher
frequency are called anti-Stokes' lines.
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• Raman further observed that the difference between the frequency of the incident light and that of a particular scattered line was constant depending only upon the nature of the substance being irradiated and was completely independent of the frequency of the incident light. If vi is the frequency of the incident light and vs' that of particular incident light and vs' that of particular scattered line, the difference v = vi - vs is called Raman frequency or Raman shift.
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EXPLANATION FOR OBSERVING
RAYLEIGH LINE
AND RAMAN LINES
• Elastic and inelastic collisions between the
radiations and interacting molecules results in the
formation of Rayleigh and Raman lines. formation of Rayleigh and Raman lines.
• In terms of excitation of electrons
• vabs = ve Rayleigh line
• vabs > ve Stokes line
• vabs < ve Anti Stokes line
•
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POLARIZABILITY OF MOLECULES
AND RAMAN SPECTRA
• The Raman effect arises on account of the polarization
(distortion of the electron cloud) of the scattering
molecules that is caused by the electric vector of the
electromagnetic radiation. The induced dipole moment electromagnetic radiation. The induced dipole moment
depends upon the strength of the electric field E and the
nature of the molecules represented by α
• μ= αE
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• In case of atoms or spherically symmetrical
molecules (spherical rotors) such as CH4' SF6
etc same polarizability is induced whatever be
the direction of the applied electric field.
They are said to be isotropically polarizable.
Such molecules are said to be isotropic
molecules.molecules.
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• In case of all diatomic molecules
(homonuclear or heteronuclear) or non-
spherical molecules (non-spherical rotors), the
polarizability depends upon the direction of
the electric field.
• Such molecules are, therefore, said to
anisotropically polarizable.anisotropically polarizable.
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Types of molecules showing Rotational
Raman Spectra.
• A molecule scatters light because it is polarizable. Hence the gross selection rule for
a molecule to give a rotational Raman
spectrum is that the polarizability of the
molecule must be anisotropic i.e. the molecule must be anisotropic i.e. the
polarizability of the molecule must depend
upon the orientation of the molecule with
respect to the direction of the electric field.
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• Hence all diatomic molecules, linear
molecules and non-spherical molecules give
Raman spectra i.e. they are rotationally
Raman active. On the other hand, spherically
symmetric molecules such as CH4' SF6 etc. do symmetric molecules such as CH4' SF6 etc. do
not give rotational Raman spectrum i.e. they
are rotationally Raman inactive. (These
molecules are also rotationally microwave
inactive).
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PURE ROTATIONAL RAMAN SPECTRA OF
DIATOMIC MOLECULES
• The selection rules for pure rotational Raman spectra of diatomic molecules are
• ΔJ = 0 , + 2• ΔJ = 0 , + 2
•• The selection rule ΔJ = 0 corresponds to
Rayleigh scattering whereas selection rule
• ΔJ = + 2 gives rise to Raman lines as explained .
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INTENSITIES OF LINES OF THE PURE
ROTATIONAL RAMAN SPECTRA
• As explained earlier, the intensities of lines
depend upon the population of initial level
from where the molecules are excited or de-from where the molecules are excited or de-
excited to the final level. Since the population
of rotational energy levels is as shown in Fig.
therefore the intensities of the Stokes' and
anti-Stokes' lines vary in a similar manner.
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APPLICATION OF PURE ROTATIONAL
RAMAN SPECTRA
• From the pure rotational Raman spectra,
noting the separation between the lines, the
value of B can be obtained from which the
moment of inertia and the bond length of the moment of inertia and the bond length of the
diatomic molecules can be calculated
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ADVANTAGES OF RAMAN SPECTROSCOPY
OVER INFRA-RED SPECTROSCOPY
• Raman frequencies are independent of the
frequency of the incident radiation, hence by
suitable adjusting the frequency of the suitable adjusting the frequency of the
incident radiation, Raman spectra can be
obtained in the visible spectrum
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• Raman spectra can be obtained even for
molecules such as O2' N2' C12 etc. which have
no permanent dipole moment. Such a study
has not been possible by infra-red
spectroscopy.
• Raman spectra can be obtained not only for
gases but even for liquids and solids whereas
infra-red spectra for liquids and solids are
quite diffuse.
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THANK YOU THANK YOU THANK YOU THANK YOU THANK YOU THANK YOU THANK YOU THANK YOU
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Thermodynamics
GHULE N BGHULE N B
Temperature, Heat, Work
Heat Engines
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Introduction
• In mechanics we deal with quantities such as
mass, position, velocity, acceleration, energy,
momentum, etc.
• Question: What happens to the energy of a • Question: What happens to the energy of a
ball when we drop it on the floor?
• Answer: It goes into heat energy.
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• In Thermodynamics we deal with quantities
which describe our system, usually (but not
always) a gas.
• Volume, Temperature, Pressure, Heat Energy, • Volume, Temperature, Pressure, Heat Energy,
Work.
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• We all know about Volume.
• Pressure:
ForcePressure =
Area
ForcePressure =
Demonstrations: Balloons, Bed of Nails, Magdeburg hemispheres.
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Temperature and Heat
• Everyone has a qualitative understanding of
temperature, but it is not very exact.
• Question: Why can you put your hand in a
400° F oven and not get instantly burned, but 400° F oven and not get instantly burned, but
if you touch the metal rack, you do?
• Answer: Even though the air and the rack are
at the same temperature, they have very
different energy contents.
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Construction of a Temperature Scale
• Choose fixed point temperatures that are easy to reconstruct in any lab, e.g. freezing point of water, boiling point of water, or anything else you can think of.
• Fahrenheit: Original idea: • Fahrenheit: Original idea:
0°F Freezing point of Salt/ice
100°F Body Temperature
Using this ice melts at 32°F and water boils at 212°F (Not overly convenient) Note: 180°F between boiling an freezing.
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• Celsius (Centigrade) Scale:
0°C - Ice Melts
100°C - Water Boils
Note a change of 1°C = a change of 1.8°F.
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Conversion between Fahrenheit and
Celsius
325
9
Fahrenheit want and Celsius know weIf
+= CF
( )329
5C
Celsius want and Fahrenheit know weIf
325
−=
+=
F
CF
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Absolute or Kelvin Scale
• The lowest possible temperature on the
Celsius Scale is -273°C.
• The Kelvin Scale just takes this value and calls
it 0K, or absolute zero.it 0K, or absolute zero.
• Note: the “size” of 1K is the same as 1°C.
• To convert from C to K just add 273.
K=C+273
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When do you use which scale.
• Never use Fahrenheit, except for the weather.
• You can always use Kelvin and you must use
Kelvin when doing absolute temperature
measurements.measurements.
• You can use either Kelvin or Celsius when
measuring differences in temperature.
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Heat
• Heat is the random
motion of the particles in
the gas, i.e. a “degraded”
from of kinetic energy.from of kinetic energy.
• Nice web simulation
• gas simulation
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Specific Heat
• Observational Fact: It is easy to change the temperature of some things (e.g. air) and hard to change the temperature of others (e.g. water)
• The amount of heat (Q) added into a body of mass m to change its temperature an amount ∆T is given by
Q=m C ∆T
• C is called the specific heat and depends on the material and the units used.
• Note: since we are looking at changes in temperature, either Kelvin or Celsius will do.
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Units of Heat
• Heat is a form of energy so we can always use
Joules.
• More common in thermodynamics is the
calorie: By definition 1 calorie is the amount calorie: By definition 1 calorie is the amount
of heat required to change the temperature of
1 gram of water 1°C.
• 1 Cal = 1 food calorie = 1000 cal.
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Units of Specific Heat
=
=
∆=
Ckg
J
Cg
cal
Tm
QC
oo∆ CkgCgTm
Note that by definition, the specific heat of water is 1 cal/g°C.
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Heat Transfer Mechanisms
1. Conduction: (solids--mostly) Heat transfer
without mass transfer.
2. Convection: (liquids/gas) Heat transfer with
mass transfer.mass transfer.
3. Radiation: Takes place even in a vacuum.
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Work Done by a Gas
• Work=(Force)x(distance)
=F∆y
• Force=(Presssure)x(Area)
• W=P(A∆y)
=P∆V
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First Law of Thermodynamics
Conservation of energy
• When heat is added into a system it can either
1) change the internal energy of the system
(i.e. make it hotter) or 2) go into doing work.
Q=W +∆U.Q=W +∆U.
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Heat Engines
• If we can create an “engine” that
operates in a cycle, we return to our
starting point each time and therefore
have the same internal energy. Thus, for have the same internal energy. Thus, for
a complete cycle
Q=W
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Model Heat Engine
• Qhot= W+Qcold
or
• Q -Q =W• Qhot-Qcold=W
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Efficiency
• We want to write an expression that describes
how well our heat engine works.
• Qhot=energy that you pay for.
• W=work done (what you want.)• W=work done (what you want.)
• Qcold= Waste energy (money).
Efficiency = e = W/Qhot
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• If we had a perfect engine, all of the input heat would
be converted into work and the efficiency would be 1.
• The worst possible engine is one that does no work
and the efficiency would be zero.
• Real engines are between 0 and 1
hot
cold
hot
coldhot
hot Q
Q
Q
Q
We −=−== 1
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WELCOMEWELCOMEGHULE N B
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Thermodynamics and statistical physicsIntroduction of statistical physicsphysics
T.Y.B.Sc 2018-19
Prof. Ghule N.B.
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*Introduction to statistical
Mechanics
From the seventeenth century onward it was
realized that material systemsmaterial systems could often be
described by a small number of descriptive small number of descriptive
parametersparameters that were related to one another in parametersparameters that were related to one another in
simple lawlike ways.
These parameters referred to geometric, geometric,
dynamical and thermal propertiesdynamical and thermal properties of matter.
Typical of the laws was the ideal gas lawideal gas law that
related product of pressure pressure and volumevolume of a gas
to the temperaturetemperature of the gas.
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* The main aim of this course is the investigation of generalproperties of the macroscopic systems with a large numberof degrees of dynamically freedom (with N ~ 1020 particlesfor example).
* From the mechanical point of view, such systems are verycomplicated. But in the usual case only a few physicalparameters, say temperature, the pressure and the density,are measured, by means of which the ’’state’’ of the systemis specified.
* A state defined in this cruder manner is called aa macroscopicmacroscopicstatestate or thermodynamic state. On the other hand, from adynamical point of view, each state of a system can bedefined, at least in principle, as precisely as possible by
*Microscopic and
Macroscopic state
dynamical point of view, each state of a system can bedefined, at least in principle, as precisely as possible byspecifying all of the dynamical variables of the system. Sucha state is called aa microscopicmicroscopic statestate.
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*Methodology of Thermodynamics and Statistical Mechanics
*Thermodynamics
*study of the relationships between macroscopic properties
* Volume, pressure, compressibility, …
* Statistical Mechanics (Statistical Thermodynamics)
*how the various macroscopic properties arise as a consequence
of the microscopic nature of the system
* Position and momenta of individual molecules (mechanical variables)
* Statistical Thermodynamics (or Statistical Mechanics) is a link* Statistical Thermodynamics (or Statistical Mechanics) is a link
between microscopic properties and bulk (macroscopic)
properties
Methods of QM
Methods of MM
A particular
microscopic model
can be usedr
U
The image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart your computer, and then open the file again. If the red x still appears, you may have to delete the image and then insert it again. P T V
Statistical
Mechanics
Pure mechanical variablesThermodynamic Variables
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*Equilibrium Macroscopic Properties
*Properties are consequence of average of
individual molecules
*Properties are invariant with time � Time
average
Mechanical
Properties of
Individual
Molecules
position, velocity
energy, ...
Thermodynamic
Properties
temperature, pressure
internal energy, enthalpy,...
average
over molecules
average
over time
statistical
thermodynamics
2 3 4
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*Description of States
* Macrostates : T, P, V, … (fewer variables)
* Microstates : position, momentum of each particles (~1023
variables)
* Fundamental methodology of statistical mechanics
* Probabilistic approach : statistical average
* Most probable value
* Is it reasonable ?
* As N approaches very large number, then fluctuations are * As N approaches very large number, then fluctuations are negligible
* “Central Limit Theorem” (from statistics)
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*Statistical Distribution
*n : number of occurrences
*b : a property
*
b
ni
1 2 3 4 5 6
if we know “distribution”
we can calculate the average
value of the property b
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*Normalized Distribution Function
� Probability Distribution Function
∑==
iii
iiiiii bn
bn
n
bnbP
)(
)()()(
*
b
Pi
b1 b5b4
b3b2 b6
∑ =i
ii
i
bP 1)(
∑
∑
>=<
>=<
iii
iii
PbFbF
Pbb
)()(
Finding probability (distribution) function is
the main task in statistical thermodynamics
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*Quantum theory says ,
*Each molecules can have only discrete values of energies
*Evidence
*Black-body radiation
*Planck distribution
*Heat capacities
*Atomic and molecular spectra
Energy
Levels
*
*Atomic and molecular spectra
*Wave-Particle duality
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*Configuration ....
*At any instance, there may be no molecules at ε0 ,
n1 molecules at ε1 , n2 molecules at ε2 , …
� {n0 , n1 , n2 …} configuration
*
ε0
ε2
ε1
ε3
ε4
ε5
{ 3,2,2,1,0,0}
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*Weight ....
*Each configurations can be achieved in different ways
*Example1 : {3,0} configuration � 1
ε
*
*Example2 : {2,1} configuration � 3ε0
ε1
ε0
ε1 ε
0
ε1 ε
0
ε1
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*All distributions of energy are equally
probable
*If E = 5 and N = 5 then
5 5 5
*
01234
01234
01234
All configurations have equal probability, but
possible number of way (weight) is different.
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*Boltzmann Distribution
*Molecular Partition Function
*Degeneracies : Same energy value but
q
e
e
e
N
np
i
j
i
j
ii
βε
βε
βε −
−
−
===∑
*
*Degeneracies : Same energy value but different states (gj-fold degenerate)∑
−=j
jeqβε
∑−=
jlevels
jjegq
βε
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*Similar method (Section 2) can be used to get
most probable distribution
∑−
−
== E
Ei
i j
i
e
e
N
nP β
β
*
∑j
e
Q
e
e
e
N
nP
i
j
i E
j
E
Ei
i
β
β
β −
−
−
===∑
∑−=
j
E jeQ βCanonical Partition Function
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irev
N
ii
iii wPdVdV
V
EPdEP −=−=
∂∂=∑∑
11
δ
∑∑ ∑ +==i
iii i
iiii dEPdPEPEddU )(
pdVTdSwqdU revrev −=−= δδ
*
revi
iii
ii
iii
ii dqTdSdPPdPQdPPdPE ==−=+−= ∑∑∑∑ ln1
)lnln(1
ββ
The only function that links heat (path integral) and
state property is TEMPERATURE.
kT/1=β
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*Internal Energy
Ei
qsi
Eii
ii
eEQ
eEQ
PEEU
i
i
)(
1
−=
∂∂
==>==<
∑
∑∑
−
−
ββ
β
*VNVN
qsii
VN
QU
eE
,,
)(,
ln1
∂∂−=
∂∂−=
−=
∂ ∑
ββ
β
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* Ensemble approach for open system
*Useful for open systems and mixtures
*Walls are replaced by permeable walls
Large reservoir (constant T )
*
All the ensemble members have the same (V, T,
Energy and particles can be exchanged
Number of Systems : N
N � ∞
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*Similar approach as Canonical Ensemble
*We cannot use second postulate because systems are
not isolated
* After equilibrium is reached, we place walls around
ensemble and treat each members the same method
used in canonical ensemble
After
*
After
equilibrium
T,V,µ T,V,N1
T,V,N2
T,V,N3
T,V,N4
T,V,N5
Each members are (T,V,N) systems
� Apply canonical ensemble methods for each member
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*The formalism of statistical mechanics relies very
much at the microscopic states.
*Number of states , sum over states
* convenient for the framework of quantum mechanics
* What about “Classical Sates” ?
* Classical states
* We know position and velocity of all particles in the
system
*
system
* Comparison between Quantum Mechanics and Classical
Mechanics
ψψ EH =QM Problem Finding probability and discrete energy states
maF =CM Problem Finding position and momentum of individual molecules
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THANK YOUTHANK YOUTHANK YOUTHANK YOUTHANK YOUTHANK YOUTHANK YOUTHANK YOU
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WEL COMEWEL COME
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Heat and
Thermodynamics Introduction of thermodynamicsIntroduction of thermodynamics
F.Y.B.Sc – 2018-19
Prof. Ghule N.B.
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Thermodynamics
Temperature, Heat, Work
Heat Engines
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Introduction
• In mechanics we deal with quantities such as
mass, position, velocity, acceleration, energy,
momentum, etc.
• Question: What happens to the energy of a • Question: What happens to the energy of a
ball when we drop it on the floor?
• Answer: It goes into heat energy.
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• In Thermodynamics we deal with quantities
which describe our system, usually (but not
always) a gas.
• Volume, Temperature, Pressure, Heat Energy, • Volume, Temperature, Pressure, Heat Energy,
Work.
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• We all know about Volume.
• Pressure:
ForcePressure =
Area
ForcePressure =
Demonstrations: Balloons, Bed of Nails, Magdeburg hemispheres.
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Temperature and Heat
• Everyone has a qualitative understanding of
temperature, but it is not very exact.
• Question: Why can you put your hand in a
400° F oven and not get instantly burned, but 400° F oven and not get instantly burned, but
if you touch the metal rack, you do?
• Answer: Even though the air and the rack are
at the same temperature, they have very
different energy contents.
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Construction of a Temperature Scale
• Choose fixed point temperatures that are easy to reconstruct in any lab, e.g. freezing point of water, boiling point of water, or anything else you can think of.
• Fahrenheit: Original idea: • Fahrenheit: Original idea:
0°F Freezing point of Salt/ice
100°F Body Temperature
Using this ice melts at 32°F and water boils at 212°F (Not overly convenient) Note: 180°F between boiling an freezing.
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• Celsius (Centigrade) Scale:
0°C - Ice Melts
100°C - Water Boils
Note a change of 1°C = a change of 1.8°F.
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Conversion between Fahrenheit and
Celsius
325
9
Fahrenheit want and Celsius know weIf
+= CF
( )329
5C
Celsius want and Fahrenheit know weIf
325
−=
+=
F
CF
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Absolute or Kelvin Scale
• The lowest possible temperature on the
Celsius Scale is -273°C.
• The Kelvin Scale just takes this value and calls
it 0K, or absolute zero.it 0K, or absolute zero.
• Note: the “size” of 1K is the same as 1°C.
• To convert from C to K just add 273.
K=C+273
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When do you use which scale.
• Never use Fahrenheit, except for the weather.
• You can always use Kelvin and you must use
Kelvin when doing absolute temperature
measurements.measurements.
• You can use either Kelvin or Celsius when
measuring differences in temperature.
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Heat
• Heat is the random
motion of the particles in
the gas, i.e. a “degraded”
from of kinetic energy.from of kinetic energy.
• Nice web simulation
• gas simulation
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Specific Heat
• Observational Fact: It is easy to change the temperature of some things (e.g. air) and hard to change the temperature of others (e.g. water)
• The amount of heat (Q) added into a body of mass m to change its temperature an amount ∆T is given by
Q=m C ∆T
• C is called the specific heat and depends on the material and the units used.
• Note: since we are looking at changes in temperature, either Kelvin or Celsius will do.
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Units of Heat
• Heat is a form of energy so we can always use
Joules.
• More common in thermodynamics is the
calorie: By definition 1 calorie is the amount calorie: By definition 1 calorie is the amount
of heat required to change the temperature of
1 gram of water 1°C.
• 1 Cal = 1 food calorie = 1000 cal.
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Units of Specific Heat
=
=
∆=
Ckg
J
Cg
cal
Tm
QC
oo∆ CkgCgTm
Note that by definition, the specific heat of water is 1 cal/g°C.
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Heat Transfer Mechanisms
1. Conduction: (solids--mostly) Heat transfer
without mass transfer.
2. Convection: (liquids/gas) Heat transfer with
mass transfer.mass transfer.
3. Radiation: Takes place even in a vacuum.
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Work Done by a Gas
• Work=(Force)x(distance)
=F∆y
• Force=(Presssure)x(Area)
• W=P(A∆y)
=P∆V
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First Law of Thermodynamics
Conservation of energy
• When heat is added into a system it can either
1) change the internal energy of the system
(i.e. make it hotter) or 2) go into doing work.
Q=W +∆U.Q=W +∆U.
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Heat Engines
• If we can create an “engine” that
operates in a cycle, we return to our
starting point each time and therefore
have the same internal energy. Thus, for have the same internal energy. Thus, for
a complete cycle
Q=W
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Model Heat Engine
• Qhot= W+Qcold
or
• Q -Q =W• Qhot-Qcold=W
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Efficiency
• We want to write an expression that describes
how well our heat engine works.
• Qhot=energy that you pay for.
• W=work done (what you want.)• W=work done (what you want.)
• Qcold= Waste energy (money).
Efficiency = e = W/Qhot
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• If we had a perfect engine, all of the input heat would
be converted into work and the efficiency would be 1.
• The worst possible engine is one that does no work
and the efficiency would be zero.
• Real engines are between 0 and 1
hot
cold
hot
coldhot
hot Q
Q
Q
Q
We −=−== 1
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