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Physics and Astronomy
THERMAL PHYSICS
U. MOHIDEEN
OUTLINEConcept of Temperature
-How to Measure T? (Kelvin Scale)
- What is Temperature? (Kinetic Theory of Gases)
Concept of Heat & Heat Energy
First Law of Thermodynamics & Energy Conservation
Understanding of Work DoneTeaching Awards
1 Distinguished Teacher of the Year 1 Distinguished Teaching Innovation Award
Junior Faculty Research Awards5 US National Science Foundation Career Award Winners 3 US Department of Energy Young Investigator Award Winners2 US Office of Naval Research Young Investigator Award Winners1 Sloan Foundation Fellow
Senior Faculty Research Awards7 American Physical Society Fellows3 American Association Advancement Science Fellows1 Guggenheim, 1 Humboldt1 Bardeen Prize1 Am. Physics Soc. Panofsky Prize
Zeroth Law (Idea of Temperature)
1. Idea of Thermal Equilibrium- Two bodies in contact have no thermal change between them
2. Temperature- Measure of Warmth (use thermometer or hands etc as something to measure)
3. Zeroth Law: Defines the idea of Temperature. If Object A in equilibrium with C (thermometer) and Object B in equilibrium with C, then A and B at same temperature as C.
How to Measure Temperature
1. Scales (Renkin, Faranheit, Kelvin)
2. Meaning of Absolute Scale
Meaning of Temperature1. Kinetic Energy of Atoms & Molecules a. Kelvin Scale (constant volume Thermometer) PV=N kBT
b. Maxwell’s Kinetic Theory (½ m<vx-avg>2 = ½ kB T) vrms= √3kBT/m
N2 molecule velocity at room temperature=510m/s 1140 mph !
Thermal Energy or Heat Energy
Joules Experiments Proving Heat Energy is
Kinetic Energy of Atoms & Molecules
- Total Kinetic Energy of gas Internal Energy
Heat Energy Q proportional to # of atoms
proportional change in T
proportional degrees of freedom
Latent Heat= Bond Energy
First Law of Thermodynamics
Energy Conservation
DU = Q - W
Total Kinetic Energy of gas Internal Energy (U)
Q= Heat Energy change- Heat Gain is Positive
Heat Lost is Negative from T change
W= Work done by gas (Expands is positive &
Compressed is negative)
Explain Work done ON and Work done BY
Work Done W=
Gas Processes:Iso thermal (Constant T)Iso baric (Constant P)Iso volumetric (Constat V) Adiabatic (No change in Q i.e. Q=0)
Area under curve if P along y axis and V along x axis
Second Law of Thermodynamics
Defines Direction of Heat Flow-
“Heat Flows from a hot object to cold object”
Information not in First Law
Need new parameter to define this:
Entropy (S)
Change in Entropy = ΔS = = (if constant T)
Second Law of Thermodynamics
Defines Direction of Heat Flow-
“Heat Flows from a hot object to cold object”
Information not in First Law
Need new parameter to define this:
Entropy (S)
Change in Entropy = ΔS = = (if constant T)
Second Law of Thermodynamics
Heat never spontaneously flows from a cold object to a hot object
or
The total entropy of an isolated system that undergoes change cannot decrease
(=0 for Reversible processes)
Eg: Drop ice into lake. Ice gains entropy> lake loses
entropy (Note net heat energy change is 0 but
Tice < Tlake)
Statistical Definition of Entropy
Entropy increase Disorder Increase
(Eg. Melting, Rotting etc)
To decrease entropy and create order, need to do work i.e. Not spontaneaous Process.
Eg. Crystallization by cooling, Body functions with
eating
Heat Engine
Hot Reservoir(Steam Tank)
Cold Reservoir(Outside Air)
Engine Work
Qhot
Qcold thru exhaust
Effeciency=
http://www.animatedengines.com/otto.shtml
All Real Process
No perpetual motion machines
Energy wasted in every process
Net Entropy increase as Spontaneous Change will happen (waste)
Food Chain - Fewer Predators
Effeciency= == 1-
Effeciency < 1
Thank You
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