lecture22

lecture22 - Phys 2101 Gabriela Gonzlez Zeroth law of...

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1 Phys 2101 Gabriela González 2 Zeroth law of thermodynamics : If bodies A and B are each in thermal equilibrium with a third body T, then they are in thermal equilibrium with each other. Or: every body in thermal equilibrium has a well defined “temperature”. When two bodies have the same temperature, they are in thermal equilibrium.
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2 3 On small scale, temperature is a measure of the vibration of the atoms in the material (solid, gas or fluid). SI unit: kelvin (K) There is an absolute minimum temperature (when all the atoms are still). That temperature is zero kelvin. There is a special temperature at which ice, water and vapor coexist: “triple point of water”. This temperature is defined as 273.16 K. Other common scales: Celsius ( o C): T c =T-273.15. ice-water temperature =0 o C, boiling water =100 o C. Fahrenheit ( o F): T F =(9/5)T C +32. (0 o F=brine temperature; 100 o F~human body temperature) a) Normal Body temperature is 98.6 o F. What is it in kelvins and o C? b) Comfort level is usually accepted to be 68 o F. What is it in kelvins and o C? Fahrenheit, Daniel Gabriel (1686-1736) Lord Kelvin (1824-1907) Anders Celsius 1701-1744 T c =(98.6-32)*5/9=37 o C T k =37+273.15=310.15 K T c =(68-32)*5/9=20 o C T k =20+273.15=293.15 K 4 When temperature changes, solid bodies change their length, and all bodies change their volume according to: Δ L = L α Δ T with α = coefficient of linear expansion Δ V = V β Δ T with β = coefficient of volume expansion If a body has a length L 0 at temperature T 0 , what is its length at a temperature T? L(t) = L 0 + Δ L = L 0 +L 0 αΔ T = L 0 (1+ αΔ T)
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3 5 A highway is made of concrete slabs that are 15m long at 20 o C. (a) If the temperature range at the location of the highway is from -20 o C to +40 o C, what size expansion gap should be left (measured at 20 o C) to prevent buckling of the highway? Concrete has a coefficient of linear expansion
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lecture22 - Phys 2101 Gabriela Gonzlez Zeroth law of...

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