14 Chapter 15: Thermodynamics
This is the last unit of PHYS 201, but starts on the second volume of the textbook, and chapter numbering starts over. Since we don’t cover everything in the thermodynamics unit, we’ll combine some of the more useful parts of the four chapters on thermodynamics here into one section.
Section 15.1: Temperature Scales
Textbook Section 1.1: Temperature and Thermal Equilibrium
Textbook Section 1.2: Thermometers and Temperature Scales
Heat is defined as the energy transferred from one system to another due to a temperature difference in the systems. Heat always flows from the hot system from the cold system; it never flows in the other direction.
Temperature is a measure of the kinetic energy of the particles making up a system. Thermodynamics refers to heat exchange between systems. A thermometer is an instrument that measures temperature by the way certain materials respond to changes in heat content. When systems are in thermal equilibrium with each other, the systems have identical temperatures and no more heat is being exchanged between the systems. An insulator attempts to prevent the transfer of heat from a hot system (say, a coffee mug) to a colder one (the air your classroom).
There are three main temperature scales you will run into. Each scale picks two set points (a certain fluid at a certain density and pressure, thus a certain temperature) and determines the size of the scale steps between and around these points. The Fahrenheit scale uses the freezing point of water (32 F on the Fahrenheit scale) and boiling point of water (212 F on the Fahrenheit scale) to define temperature. There are 180 F between these two points.
The Celsius scale also uses the freezing and boiling points of water, but on the Celsius scale, these points occur at 0 C and 100 C. There are only 100 C steps between these two points. Therefore, a change of one degree C is \emph{not} equivalent to a change of one degree C.
To convert back and forth between these systems, use the conversions below.
Gas thermometers are the most accurate thermometers, but are not commonly used because they can take up entire rooms. In a gas thermometer, as the temperature of the fluid enclosed increases, so does the temperature. Every different type of fluid changes differently with pressure. When graphed (temperature vs pressure), all the lines appeared to be converging at a single point in the negative part of the Celsius temperature range. This temperature that all fluids can theoretically reach (but we’ve never quite gottenabsolute zero any of them all the way there) is called absolute zero, and is the basis of the third temperature scale, the Kelvin scale.
The Kelvin scale starts at absolute zero (basically no motion of particles at all in anything) and goes up from there. It hits the freezing point of water at 273.15 K (note we don’t use “degrees” when talking about Kelvin), so the conversion from Celsius to Kelvin is
Section 15.2: Thermal Expansion
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