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 EnergyFirst Law of Thermodynamics & Energy ConservationUnderstanding of Work Done

Teaching Awards1 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 Temperature1. 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 freedomLatent 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 EngineHot 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 machinesEnergy wasted in every processNet Entropy increase as Spontaneous Change will happen (waste)Food Chain - Fewer Predators

Effeciency= == 1-

Effeciency < 1

Thank You