First Law of ThermodynamicsPAL #12 TemperatureWhich of the following places the temperatures in the correct rank, highest to lowest?Consider 3 aluminum plates, plate A has area of 1X1 m, plate B has area of 2X2 m and plate C has area of 3X3 m. If the temperature of the plates is raised by 10 degrees, which plates has the greatest increase in area?Heat CapacitySpecific HeatMolar Specific HeatHeat of TransformationVaporization and FusionPhase Curve for WaterCalorimetryWork and Internal EnergyWork and HeatWork, Heat and Internal EnergyThe First Law of ThermodynamicsWork, Pressure and Volumep-V DiagramsThe p-V CurveAdiabaticConstant VolumeCyclical ProcessNext TimeFirst Law of ThermodynamicsPhysics 202Professor Lee CarknerLecture 13PAL #12 TemperatureHow does the Galileo thermometer work? The water in the tube changes density with TWater gets more dense as T drops and so the balls rise up (80 to 64) Galileo thermometer’s limitationsNot very precise (balls marked in 4 degree increments)Not much range (64-80 F)FragileWhich of the following places the temperatures in the correct rank, highest to lowest?a) 50 X, 50 W, 50 Yb) 50 X, 50 Y, 50 Wc) 50 W, 50 X, 50 Yd) 50 Y, 50 W, 50 Xe) 50 Y, 50 X, 50 WConsider 3 aluminum plates, plate A has area of 1X1 m, plate B has area of 2X2 m and plate C has area of 3X3 m. If the temperature of the plates is raised by 10 degrees, which plates has the greatest increase in area?a) Ab) Bc) Cd) All tiee) You cannot tell with out knowing the thicknessHeat CapacityThe amount of heat needed to change the temperature of an object depends on the object’s thermal properties Which has the higher temperature?Heat capacity (unit energy per Kelvin) is given by:Q = C (Tf - Ti) = C TWhere:Q = C = C is a property of a specific objectSpecific Heat C=cmWhere m is the mass and c is the specific heat Each type of substance has a c (e.g. water, iron, etc.) Q = cm(Tf - Ti)Amount of heat (Q) needed to change the temperature of m kg of a certain type of substance from Ti to TfMolar Specific Heat One mole = 6.02 X 1023 atoms or moleculesWe need to use a modified version of the last formula:Q = cmol (# of moles) (Tf - Ti)Heat of Transformation Boiling water stays at 100 deg C, the added energy goes into transforming the water from liquid to gas Q = L mWhere L is the heat of transformationVaporization and Fusion For the phase change from solid to liquid the heat of fusion, LF is needed The total heat necessary to change temperature and state is the sum of heats required for eachPhase Curve for WaterCalorimetry1) Write out equation adding all heats in symbolic form and set equal to zero 2) Substitute numbers, use correct values for c and L 3) Make sure units for m, c, L and T match 4) Always use T = Tf-Ti Temperature decrease results in a negative loss of heat5) For Lm, make positive if heat is absorbed and negative if heat is given ofSolve for required variableWork and Internal Energy No heat can travel in or outIf weight is removed from the piston head the remaining weight will rise Where does the energy come from?It must come from the internal energy of the gasWork and Heat The thermal reservoir can add or subtract heat from the system What happens to the internal energy of the system as heat is applied or work is done?Work, Heat and Internal Energy If we add weight and do 6 J of work we either increase the internal energy by 6 J or produce 6 J of heat or some combination that adds up to 6Energy is conserved!The First Law of ThermodynamicsThis conservation of energy is called the First Law of ThermodynamicsEint = Q - W Sign convention:If work is done by the system W is positive, if work is done on the system W is negativeWork, Pressure and VolumeHow does work change the system? The amount of work done in moving something a small distance ds is: However, F = pA and dV = A ds The total work is dW integrated over the volume changeW =  dW =  p dV (integrated from Vi to Vf)Work is the area under the curve on a p-V diagramp-V DiagramsThe p-V CurvePressure must be non-zero in order for work to be done  If the volume decreases, work is done on the system and the work is negative If the process is cyclical and returns to the same point by two diferent paths the area between the paths is equal to the work (and also equal to the heat)Adiabatic Q=0 so Eint = -W Consider a thermally isolated (insulated) piston with weight on topNo heat can get in or outBy changing the weight, the gas is compressed or expandsConstant Volume Eint = QIf any heat is applied to the system it goes directly into internal energy The gas cannot expandCyclical Process The final pressure, volume and internal energy are the same as the initialEint = 0 so Q=W Important for enginesNext TimeRead: 18.11-18.12Homework: Ch 18, P: 31, 39, 43, 51,