Handout 01 - Thermodynamics.pdf - AP PHYSICS B THERMAL PHYSICS HEAT THERMODYNAMICS What you already know from Chemistry about temperature and heat Never

Handout 01 - Thermodynamics.pdf - AP PHYSICS B THERMAL...

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AP ® is a registered trademark of the College Board. The College Board was not involved in the production of and does not endorse this product. © 2009 by René McCormick. All rights reserved. AP* PHYSICS B THERMAL PHYSICS: HEAT & THERMODYNAMICS What you already know from Chemistry about temperature and heat: Never, ever forget that temperature is the average kinetic energy of molecules ( K avg = ½ mv 2 ) Metals conduct heat and electricity due to mobile, delocalized electrons. Thermal contact (commence heat exchange) leads to thermal equilibrium (cease heat exchange) Heat moves along a gradient from hot to cold until equilibrium is established HEAT --energy exchanged between objects because of a temperature difference A thermometer reaches thermal equilibrium once it stabilizes with the substance being measured There are FOUR Laws of Thermodynamics that are inconveniently numbered! Zeroth Law of Thermodynamics- -If two substances are in thermal equilibrium with a third system, then they are in thermal equilibrium with each other. What a silly name! Why do they call it that? They had already named the other laws and discovered this obvious one still needed stating, so they had to go backwards to zero. First Law of Thermodynamics --most commonly known as The Law of Conservation of Energy which really means that the total Energy, U of the universe remains constant! Second Law of Thermodynamics --The entropy [ S --I know, the word entropy has no “S” in it--I don’t decide these things! It’s just a fancy word for disorder or chaos.] of the universe is always increasing. [Think about all the energy it takes to keep your room clean and how it always gets messy “by itself”.] Third Law of Thermodynamics --The entropy of a pure crystalline substance at 0 K is equal to zero. [Perfect order and no molecular motion no disorder or chaos. Not actually attainable since electrons are still moving.] THERMOMETERS AND TEMPERATURE SCALES How thermometers work depends on the following physical properties: Δ Volume of a liquid [ Δ is the capital Greek letter delta--it’s used to mean change which is generally computed “final minus initial”] Δ Length of a solid Δ Pressure of a gas held at constant volume Δ Electric resistance of a conductor (that’s how the CBL probe works--very accurate!) Δ Color of a very hot object such as red hot iron, sun, stars
Thermal Physics Page 2

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