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Physics and Astronomy

Physics and Astronomy . THERMAL PHYSICS U. MOHIDEEN. OUTLINE. Concept 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

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Physics and Astronomy

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  1. Physics and Astronomy THERMAL PHYSICS U. MOHIDEEN

  2. OUTLINE • Concept 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 Done • Teaching Awards • 1 Distinguished Teacher of the Year • 1 Distinguished Teaching Innovation Award • Junior Faculty Research Awards • 5 US National Science Foundation Career Award Winners • 3 US Department of Energy Young Investigator Award Winners • 2 US Office of Naval Research Young Investigator Award Winners • 1 Sloan Foundation Fellow • Senior Faculty Research Awards • 7 American Physical Society Fellows • 3 American Association Advancement Science Fellows • 1 Guggenheim, 1 Humboldt • 1 Bardeen Prize • 1 Am. Physics Soc. Panofsky Prize

  3. Zeroth Law (Idea of Temperature) Idea of Thermal Equilibrium- Two bodies in contact have no thermal change between them Temperature- 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.

  4. How to Measure Temperature Scales (Renkin, Faranheit, Kelvin) Meaning of Absolute Scale

  5. Meaning of Temperature 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 !

  6. 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

  7. 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

  8. Work Done W= Area under curve if P along y axis and V along x axis Gas Processes: Iso thermal (Constant T) Iso baric (Constant P) Iso volumetric (Constat V) Adiabatic (No change in Q i.e. Q=0)

  9. 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)

  10. 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)

  11. 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)

  12. 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

  13. Heat Engine Hot Reservoir (Steam Tank) Qhot Engine Work Qcold thru exhaust Cold Reservoir (Outside Air) Effeciency= http://www.animatedengines.com/otto.shtml

  14. 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

  15. Thank You

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