Physics Subject Area Test

1. Physics Subject Area Test Thermodynamics

2. There are three commonly used temperature scales, Fahrenheit, Celsius and Kelvin. Temperature Conversions

3. Converting Between the Kelvin and Celsius Scales • Converting Between the Fahrenheit and Celsius Scales

4. Thermal expansion • Expandingsolidsmaintain original shape • Expandingliquidsconform to the container • Linear expansion ΔL = αLΔT L = length α = coefficient of liner expansion ΔT = temperature change

5. Example: The highest tower in the world is the steel radio mast of Warsaw Radio in Poland, which has a height if 646m. How much does its height increase between a cold winter day when the temperature is -35⁰C and a hot summer day when the temperature is +35 ⁰C ? ΔL = αLΔT = 12x10-6/ ⁰C x 646 x 70⁰C = 0.54m

6. Volume expansion ΔV= βVΔT L = length β = coefficient of liner expansion ΔT = temperature change cold hot Β = 3 α

7. Heat flow: the heat current; the amount of heat that passes by some given place on the rod per unit time = heat flow k = proportionality constant, thermal conductivity A = cross sectional area ΔT = change in temperature Δx = distance crossed, thickness of material Thermal Conduction

9. convection Heatisstored in a movingfluid and iscarriedfrom one place to another by the motion of thisfluid • radiation The heatiscarriedfrom one place to another by electromagneticwaves • conduction the process of handing on energy from one thing to the next

10. Amount of power radiated (I) by a body at temperature T and having a surface area A is given by the Stefan-Boltzmann law I = power radiated e = emissivity (between 0 and 1) σ = Stefan’s constant = 5.6703 x 10-8 W/m2·K A = surface area T = temperature Shiny objects are not good absorbers or radiators & have emissivity close to 0 Black objects have emissivity close to 1 Stefan-Boltzmann Law

11. Latent heat ( heat of transformation) – the heat absorbed during the change of state ΔQ = quantity of heat transferred m = mass of the material Heat of fusion - heat absorbed when changing from a solid to a liquid Heat of vaporization - heat absorbed when changing from a liquid to a gas Changes of State

13. P1V1=P2V2 P= pressure V = volume GAS LAWSBoyle’s Law

14. V1/V2=T1/T2 Charles Law • V = volume • T = temperature

15. P1/T1=P2/T2 Gay-Lussac’s Law • P = pressure • T = temperature

16. = Ideal Gas Law • P= pressure • V = volume • T = temperature • n = moles • R = Gas constant • = 0.08206 L-atm/mol K • PV = n R T Combined Gas Law

17. PV = nRT n/V = P/RT Molarity = n/V Density D = m/V Molecular WtM = m/n D=Mn/V = PM/RT M= DRT/P Gas Density

18. Energy can be neither created nor destroyed but only transformed First Law of Thermodynamics

19. Energy In = Energy OutorU2- U1= Q -W where U1: internal energy of the system at the beginning U2: internal energy of the system at the end Q : net heat flow into the system W : net work done by the system Q = ΔU + ΔW THE GENERAL ENERGY EQUATION

20. A closed tank has a volume of 40.0 m2 and is filled with air at 25⁰C and 100 kPa. We want to maintain the temperature in the tank at 25⁰C as water is pumped into it. How much heat will have to be removed from the air in the tank to fill it half full? = (100kPa) (40.0 m2)(-0.69314) = -2772.58kJ

22. Isobaric • the pressure of and on the working fluid is constant • represented by horizontal lines on a graph • Isothermal • temperature is constant • Temperature doesn’t change, internal energy remains constant, & the heat absorbed by the gas = the work done by the gas • The PV curve is a hyperbola • Adiabatic • there is no transfer of heat to or from the system during the process • Work done = decrease in internal energy & the temperature falls as the gas expands • -the PV curve is steeper than that of and isothermal expansion STATE CHANGES

23. Quasi-static (quasi-equilibrium) processes – sufficiently slow processes, any intermediate state can be considered as an equilibrium state (the macroparamers are well-defined for all intermediate states). Advantage: the state of a system that participates in a quasi-equilibrium process can be described with the same (small) number of macro parameters as for a system in equilibrium (e.g., for an ideal gas in quasi-equilibrium processes, this could be T and P). By contrast, for non-equilibrium processes (e.g. turbulent flow of gas), we need a huge number of macro parameters. For quasi-equilibrium processes, P, V, T are well-defined – the “path” between two states is a continuouslines in the P, V, T space. Examples ofquasi- equilibrium processes: Quasi-Static Processes • isochoric:V = const • isobaric:P = const • isothermal:T = const • adiabatic:Q = 0 P 2 V 1 T

24. The workdone by an external forceon a gas enclosed within a cylinder fitted with a piston: A – the piston area W = (PA) dx = P (Adx) = - PdV force The sign: if the volume is decreased, W is positive(by compressing gas, we increase its internal energy); if the volume is increased, W is negative (the gas decreases its internal energy by doing some work on the environment). x P Work W = - PdV - applies to any shape of system boundary dU = Q – PdV The work is not necessarily associated with the volume changes – e.g., in the Joule’s experiments on determining the “mechanical equivalent of heat”, the system (water) was heated by stirring.

25. SpecificHeat the heatabsorbedduring the change of state Q = nCvΔT Q = amount of heat required n = number of moles Cv = specific heat at a constant volume ΔT = Change in temperature

26. How to calculate changes in thermal energy Specific heat is the amount of heat required to raise the temperature of 1 kg of a material by one degree (C or K). C water = 4184 J / kg C Q = m x T x Cp Q = change in thermal energy m = mass of substance T = change in temperature (Tf – Ti) Cp = specific heat of substance

27. Second Law of Thermodynamics Entropy = the transformation of energy to a more disordered state - can be thought of as a measure of the randomness of a system - related to the various modes of motion in molecules The second law of thermodynamics:entropy of an isolated system not in equilibrium tends to increase over time • No machine is 100% efficient • Heat cannot spontaneously pass from a colder to a hotter object

28. The relationship between kinetic energy and intermolecular forces determines whether a collection of molecules will be a solid, liquid or a gas • Pressure results from collisions • The # of collisions and the KE contribute to pressure • Temperature increase KE Kinetic molecular theory