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p153term12k6 - Physics 153 2006 by Don Witt Thermodynamics...

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Physics 153 2006 by Don Witt Thermodynamics Thermometric Property: is a physical property that changes with “ temperature Different ways of measure temperature 1) Expansion of a fluid. 2) Electrical 3) Mechanical expansion of solid. 4) Expansion of a gas. There are many others not listed.
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Physics 153 2006 by Don Witt Thermodynamics Thermal Contact A B C A B C A B C 2) 1) 3)
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Physics 153 2006 by Don Witt Thermodynamics Thermal Contact A B C A B C A B C 2) 1) 3) None are in thermo contact A&B are in thermo contact not C Which are in thermal contact? A&C and C&B
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Physics 153 2006 by Don Witt What can we say about the temperature of the the three objects? Thermal Equilibrium: when the cooling stops. The zeroth law of thermodynamics: If two objects are in thermal equilibrium with a third, then they are in thermal equilibrium with each other.
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Physics 153 2006 by Don Witt Two objects are defined to have the same temperature if they are in thermal equilibrium with each other. How to measure temperature: Simple start is to pick at thermometric property which linear.
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Physics 153 2006 by Don Witt Mercury Thermometer example Example: Mercury Thermometer (Celsius temperature scale) L 100 L 0 L 100 is the height at boiling point of water L 0 is the height at freezing point of water
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Physics 153 2006 by Don Witt (Mercury Thermometer cont’d) t c = L 100 L 0 - L t L 0 - X 100º C Fahrenheit: t for ice if 32º F and t for boiling is 212º F
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Physics 153 2006 by Don Witt Constant volume gas thermometer Example: Constant volume gas thermometer t c = P 100 P 0 - P t P 0 - X 100º C P t
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Physics 153 2006 by Don Witt Kelvin scale The thermometer will go to P = 0 at some temperature which is -273.15ºC. Experiment give us this number along with PV T = constant We can also define a new temperature so that 0K (kelvin) is -273.15ºC and take 1K to be 1ºC.
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Physics 153 2006 by Don Witt Triple point of water as a standard Still a problem with temperature how do we calibrate the Thermometer? Namely, how do we decide when we at Freezing or boiling? The triple point of water is for pressure at 4.58mm Hg and temperature 0.01ºC.
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Physics 153 2006 by Don Witt Errors in gas thermometer T = 273.16K P P triple T P O air N H 2 2 2 446ºC 444ºC Graph of temperature as a function pressure for constant volume gas thermometer with different gases.
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Physics 153 2006 by Don Witt Thermal Expansion As the temperature changes the length of a material changes. L = α L 0 T α is a constant for the material, L is the change in length, L 0 the length, and T is the change in temperature. Not all material expand with increase in temperature.
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Physics 153 2006 by Don Witt Linear Expansion The equation can be written in the following form L = α L 0 T If Δ T is small Δ L should be small and so L 0 L , then one can take the limit of our above equation, namely, L = α L 0 α L T Thus, if Δ T 0, the expansion equation becomes dL = α L dT
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Physics 153 2006 by Don Witt Expansion coefficients The constant α is determined by the material be considered, it can be positive or negative.
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