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Overview
Physics 10: Lecture 8
EntropyPaul Leonard Atchong C. Hilario, M.Sc.
National Institute of Physics, University of the Philippines, Diliman, Quezon City, Philippines
Email: [email protected]
Conservation of Energy
Entropy
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2Physics 10: Lecture 8
Tractor beams
http://images2.wikia.nocookie.net/c!2012082102"2#1/memorya$pha/en/images/2/22/%ractor!eam.&pg
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3Physics 10: Lecture 8
Optical tweezers
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4Physics 10: Lecture 8
Optical tweezers
Light has momentum
If propagation of light changes directionthen the momentum changed
If the momentum of light changed then anet force is exerted on the light by the
particle
Light also exerts a force on the particle
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5Physics 10: Lecture 8
Last time
Objects continously move because theyhave energy
Energy comes in many forms
Energy can never be created nor destroyed
Energy can only be transformed
Conservation of energy
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6Physics 10: Lecture 8
Seven ideas that shoo the universe
.!he earth i" not the center o#the uni$er"e.
2.!he uni$er"e i" a %echani"%
run &y rule".3.Energy %a'e" it go.4.Entropy tell" it (here to go.5.!he truth" are relati$e &ut
the la( i" a&"olute.6. )ou can not 'no( or predict
e$erything.*.+unda%entally, thing" ne$er
change!Spielberg" #nderson" !even Ieas that !hoo" the Universe, $%%&!
Energy %a'e" it uni$er"e- go.
Conservation of energy
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Physics 10: Lecture 8
Seven ideas that shoo the universe
.!he earth i" not the center o#the uni$er"e.
2.!he uni$er"e i" a %echani"%
run &y rule".3.Energy %a'e" it go.4.Entropy tell" it (here to go.5.!he truth" are relati$e &ut
the la( i" a&"olute.6. )ou can not 'no( or predict
e$erything.*.+unda%entally, thing" ne$er
change!Spielberg" #nderson" !even Ieas that !hoo" the Universe, $%%&!
Entropy tell" it uni$er"e-(here to go.
Entropy
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/Physics 10: Lecture 8
The Laws of thermodynamics
'eroth Law of Thermodynamics
The first law of thermodynamics
The second law of thermodynamics
The third law of thermodynamics
Entropy
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0Physics 10: Lecture 8
The Laws of thermodynamics
'eroth Law of Thermodynamics
The first law of thermodynamics
The second law of thermodynamics
Entropy
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Physics 10: Lecture 8
(eat versus temperature
(eat is a #or% o# energy and is describedin terms of the change" in the total
energy of the molecules
Temperature is the concentration of theinternal energy and is described in termsof the a$erage energy of the molecules
)hen two systems are allowed to exchangeheat" they are said to be in ther%alcontact and &oth of their temperaturechanges
Entropy
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2Physics 10: Lecture 8
(eat versus temperature
)hen in thermal contact" the two systemsexhange energy until their te%perature
i" the "a%e
)hen this happens" they are said to be inther%al e1uili&riu%
Entropy
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3Physics 10: Lecture 8 Entropy
'eroth law of thermodynamics
#lso nown as thethermometer law
If a third object C is inthermal e*uilibriumwith both # and $
then # and $ are inthermal e*uilibrium
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4Physics 10: Lecture 8
+evisit, conservation of energy
Entropy
-or an isolated system" energy is conserved
To completely mae sense of this concept" wemust determine,
– )hich is the system and which are parts ofthe system
– )hich is not part of the system but is part ofthe environment
)e must then tae into account, – (ow much energy went in.
– (ow much energy went out.
– (ow much wor was done to the system
– (ow much wor was done by the system
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5Physics 10: Lecture 8
The $st law of thermodynamics
Essentially" a statement of the conservationof energy in a thermodynamic system
The change in the internal energy ise*ual to the energy a&"or&ed orrelea"ed
/hysics textboosInternational union for pure and applied
chemistry 0I1/#23
Entropy
ΔU =Q−W
ΔU =Q+W
h i 0 8
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6Physics 10: Lecture 8
The e*uation of state
One can use anything as a thermometer aslong as a de#inite relation"hip between
te%perature and other para%eter" exists!
These are called the e1uation o# "tate!
Example, Ideal gas law 4 P% & n'(
Entropy
Ph i 10 L 8
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*Physics 10: Lecture 8
Thermodynamic processes
)hen the process does not in$ol$e heattran"#er" it is said to be adia&atic.
)hen the process is under con"tantte%perature" the process is i"other%al.#diabatic processes are not isothermal
)hen the process is under con"tantpre""ure" the process is i"o&aric.
)hen the process is under con"tant$olu%e" the process is i"ochoric.
Entropy
Ph i 10 L t 8
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Physics 10: Lecture 8
Thermodynamic processes
Entropy
⏞
isotherms
Ph i 10 L t 8
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/Physics 10: Lecture 8
5nd Law of thermodynamics
In an i"olated "y"te%" it is i%po""i&le tore$er"e the #lo( o# heat from fromhigher temperature to lower temperature
(eat flows spontaneously from a hot to cold
On its own" heat will not flow from cold to hot
Entropy
Ph i 10 L t 8
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20Physics 10: Lecture 8
6ore on engines
Entropy
Engines convert heatinto mechanical
energySteam engines uses
steam to do this
(eat flows from ahot re"er$oir to acold re"er$oir
Physics 10: Lecture 8 E
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2Physics 10: Lecture 8
+efrigerators and aircons
Entropy
(eat flows from acold re"er$oir to
a hot re"er$oir7ot spontaneous
or' i" re1uired
0done by acompressor3
Physics 10: Lecture 8 E
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22Physics 10: Lecture 8
The perfect heat engine
Entropy
#ssume all of theheat is convertedto wor
)e can use thatwor to bring heatfrom cold to hot"essentially aworless ref
8iolate the 5nd law ofthermodynamics
perfect engine
does not exist
Physics 10: Lecture 8 E t
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23Physics 10: Lecture 8
Entropy
Is a measure of the amount of disorder inthe system
Entropy is a relative value hence absolutemeasurement is difficult! )e are howevermore concerned of the change
2hange is measured by amount of heatchange per a&"olute te%perature
Entropy
Physics 10: Lecture 8 E t
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24Physics 10: Lecture 8
Entropy
#luminum at $9 degree 2elsius is in thermalcontact with water at $99 degrees!
#luminum will get hotter and waterbecomes cooler
2hange in entropy of aluminum will be
roughly :.)* +- while that of water isroughly /.)) +- 0you may consult for thedetails3
Total change is ;!%: +-
Entropy
Physics 10: Lecture 8 Entrop
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25Physics 10: Lecture 8
Entropy
)ater at 5; degree 2elsius is in thermalcontact with water at $99 degrees!
2ool water will get hotter and warm waterbecomes cooler
2hange are e*ual in magnitude but reverse
in signs Total change is 9 +-
Entropy
Physics 10: Lecture 8 Entropy
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26Physics 10: Lecture 8
Entropy
-or re$er"i&le proce""e"" the change inentropy i" al(ay" ero
-or irre$er"i&le proce""e"" the change inentropy i" al(ay" po"iti$e
-or non"pontaneou" processes change
in entropy i" negati$eEntropy in general is increa"ing
The uni$er"e" on it" o(n" will move
to(ard" increa"ing entropy
Entropy
Physics 10: Lecture 8
Entropy
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2*Physics 10: Lecture 8
Seven ideas that shoo the universe
.!he earth i" not the center o#the uni$er"e.
2.!he uni$er"e i" a %echani"%
run &y rule".3.Energy %a'e" it go.4.Entropy tell" it (here to go.5.!he truth" are relati$e &ut
the la( i" a&"olute.6. )ou can not 'no( or predict
e$erything.*.+unda%entally, thing" ne$er
change!Spielberg #nderson !even Ieas that !hoo" the Universe $%%&
Entropy tell" it uni$er"e-(here to go.
Entropy