Physics and Astronomy

Physics and Astronomy

THERMAL PHYSICSU. MOHIDEEN

OUTLINEConcept of Temperature -How to Measure T? (Kelvin Scale) - What is Temperature? (Kinetic Theory of Gases)

Concept of Heat & Heat EnergyFirst Law of Thermodynamics & Energy ConservationUnderstanding of Work DoneTeaching Awards1 Distinguished Teacher of the Year 1 Distinguished Teaching Innovation AwardJunior 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 FellowSenior Faculty Research Awards7 American Physical Society Fellows3 American Association Advancement Science Fellows1 Guggenheim, 1 Humboldt1 Bardeen Prize1 Am. Physics Soc. Panofsky PrizeZeroth Law (Idea of Temperature)Idea of Thermal Equilibrium- Two bodies in contact have no thermal change between themTemperature- Measure of Warmth (use thermometer or hands etc as something to measure)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 TemperatureScales (Renkin, Faranheit, Kelvin)

Meaning of Absolute ScaleMeaning of TemperatureKinetic Energy of Atoms & Molecules a. Kelvin Scale (constant volume Thermometer) PV=N kBT

b. Maxwells Kinetic Theory ( m2 = kB T) vrms= 3kBT/m

N2 molecule velocity at room temperature=510m/s 1140 mph ! Chemical reactions, cooling in refridgerator, body temperature, fever, frost bite

5Thermal Energy or Heat EnergyJoules 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 freedomLatent Heat= Bond Energy6First Law of ThermodynamicsEnergy 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 U=3/2NKBT7Work Done 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 axisSecond Law of ThermodynamicsU=3/2NKBT9Second Law of ThermodynamicsU=3/2NKBT10Second Law of ThermodynamicsU=3/2NKBT11Statistical Definition of EntropyEntropy 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 eatingU=3/2NKBT12Heat EngineHot Reservoir(Steam Tank)Cold Reservoir(Outside Air)EngineWorkQhotQcold thru exhausthttp://www.animatedengines.com/otto.shtmlIdeally Simplest Isothermal during heat transfer and adiabatic during remainder of cycle. Carnot engine.QH/Qc= TH/Tc as Delta S for cycle=0 13All Real Process No perpetual motion machinesEnergy wasted in every processNet Entropy increase as Spontaneous Change will happen (waste)Food Chain - Fewer Predators

Effeciency < 1U=3/2NKBT ideal gas Body temperature determined by skin thickness and outside TBirds with better insulation operate at higher T14

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