advertisement

Thermal Physics • Too many particles… can’t keep track! • Use pressure (p) and volume (V) instead. • Temperature (T) measures the tendency of an object to spontaneously give up/absorb energy to/from its surroundings. (p and T will turn out to be related to the too many particles mentioned above) • p, V, and T are related by the equation of state: f(p,V,T) = 0 e.g. pV = NkBT • Heat is energy in transit and it is somehow related to temperature Zeroth law of thermodynamics A C If two systems are separately in thermal equilibrium with a third system, they are in thermal equilibrium with each other. Diathermal wall B C C can be considered the thermometer. If C is at a certain temperature then A and B are also at the same temperature. Temperature scales • Assign arbitrary numbers to two convenient temperatures such as melting and boiling points of water. 0 and 100 for the celsius scale. • Take a certain property of a material and say that it varies linearly with temperature. X = aT + b • For a gas thermometer: P = aT + b • X can also be resistance, capacitance, etc. • Temperature is related to heat and somehow related to the motion of particles • Need an absolute definition of temperature based on fundamental physics • A purely thermal physics definition is based on the Carnot engine • Can also be defined by statistical arguments Most likely macrostate the system will find itself in is the one with the maximum number of microstates. E1 E2 1(E1) (E) 2(E2) 1 d ln 1 d ln 2 dE1 dE2 k BT