Temperature

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# Temperature - PowerPoint PPT Presentation

Temperature Physics 313 Professor Lee Carkner Lecture 2 Thermodynamics Thermodynamics is the study of energy e.g. a cylinder of gas accelerated to high speed has an increased kinetic energy but the same temperature

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Presentation Transcript
Temperature

Physics 313

Professor Lee Carkner

Lecture 2

Thermodynamics
• Thermodynamics is the study of energy
• e.g. a cylinder of gas accelerated to high speed has an increased kinetic energy but the same temperature
• We will discuss the properties of a system and how they relate to internal energy, through both the macroscopic and microscopic points of view
Specify a few basic bulk properties

Classical Thermodynamics

Specify states of individual units

Statistical mechanics

Macroscopic Microscopic
Systems
• Material separated from its surroundings by a boundary
• Closed
• e.g. gas in a piston
• Open
Processes
• State
• Process
• Quasi - Static (Quasi-Equilibrium) Process
• slow changes
• Non-quasi static processes are discontinuous
Equilibrium
• Define two properties for a system
• If the two properties remain constant the system is in equilibrium
• A system is in equilibrium with itself if its properties are constant throughout the whole system
System Boundaries
• thermal insulator
• Dithermal wall
• thermal conductor
Temperature Proxies
• Changes in temperature cause changes in other system properties
• Two consequences:
• We measure T by measuring changes in other properties
• If T is not constant, nothing else is
• Often given at standard temperature (0 C) or room temperature (20 C)
Thermal Expansion
• The degree to which a linear distance varies with temperature is given by:
• Change in one dimension (linear expansion)
• Very small (~one part in a million per degree) in most cases
• Note that a itself is temperature dependant
The Brooklyn Bridge
• Built:
• Designed: John A Roebling
• Chief Engineer: Washington A. Roebling
• Height:
• Length:
• World’s longest suspension bridge until 1903
• The Great Bridge : The Epic Story of the Building of the Brooklyn Bridge by David McCullough
Thermal Equilibrium
• Two systems separated by a dithermal wall that do not change properties
• If the two systems are not in thermal equilibrium they will exchange heat until they are
Zeroth Law
• Three systems A, B and T
• A and T --
• B and T --
• Then for A and B
• Two systems in thermal equilibrium with a third are in thermal equilibrium with each other
Isotherms
• Plot pressure and volume
• Curve is called an isotherm
• Temperature determines thermal equilibrium
Temperature
• Take an object T and mark it so that changes in its properties can be measured
• Calibrate the measurements so that your scale corresponds to universally accepted situations
• e.g. mercury thermometer
Temperature Scales
• Gabriel Daniel Fahrenheit invented the mercury thermometer in 1714
• 32 F is freezing point of water, 212 is chosen for boiling point (32+180)
• Anders Celsius introduced his scale in 1742
• William Thomson, Lord Kelvin, developed the absolute (Kelvin) scale from his analysis of ideal engines
Temperatures
• Universe (Planck time) ~
• Universe (today) ~
• Average star ~
• Average dust cloud ~
• Planet (Mercury) ~
• Planet (Neptune) ~
• Planet (habitable) ~