Presentation on theme: "The density of copper is 8.2 g/cm 3. Find A.The number of atoms in one cubic centimeter of copper. B.The average distance between the atoms. Repeat for."— Presentation transcript:
The density of copper is 8.2 g/cm 3. Find A.The number of atoms in one cubic centimeter of copper. B.The average distance between the atoms. Repeat for silver (density 10.49 g/cm 3 ).
Heat energy Q (1 cal = 4.182 Joule) –Energy transfer in a process due to temperature differences –Q=mc T –Heat is not the only way to change temperature Specific heat?
Cold Cup Room temperature 20 C m=150 g Hot Coffee T=90 C M=150 g Where do you think the temperature of cup and coffee combined will end up after 30 s? a)closer to 90 C b)at the average temperature 55 C c)closer to 20 C after 2 hours
Latent heat Pot of ice on a hot plate at constant heating rate Q1 Q2Q3 No change in TQ changes TNo change in T
Latent heat Energy transferred due to temperature differences with the environment Q=mL Latent heat does not change temperature of system (“hidden” = latent) Latent heat: adds PE Sensible heat: adds KE (changes T)
A New Years Custom On New Years Eve, it is a custom in German-speaking regions to melt a small amount of lead and pour it into water. The created shapes are interpreted as symbolic for what the next year may bring to the pourer. A bowl contains 300 g of water and 150 g of ice chips. How much molten lead needs to be added in order to melt all the ice?
Of the following choices, which can be used in order to produce water of 50 C by mixing? (Consider equal amounts) 100 C steam and 0 C water 100 C water and 0 C water 100 C water and 0 C ice 100 C steam and 0 C ice
Transfer of heat Why is the coffee cooling down?
Heat transfer processes Convection Radiation http://www.morris.umn.edu/~sboyd/index_files/Thermal%20images.htm http://www.morris.umn.edu/~sboyd/index_files/Thermal%20images.htm http://www.morris.umn.edu/~sboyd/weather/cloudthermal.htm Heat conduction Coefficient of thermal conductivity
Heat conduction k Coefficient of thermal conductivity Aluminum210 W/(m K) Glass 0.9 W/(m K) T1 T2 < T1 L A Water 0.58 W/(m K) Air0.026 W/(m K) Q
Window Find the heat lost to the environment through a window of 1.20m by 1.20m area during a winter night (12 h). The indoor temperature is +20 C, while the outdoor temperature is -20C. a)The window consists of 15 mm of glass. b)The window consists of two 5-mm panes with a gap of 5mm air in-between.
Remove the ice build-up or not? Two faculty members argue whether the ice should be removed from the lounge refrigerator or not in order to save energy. –A claims that the ice in the compartment provides enough thermal mass to keep the contents cold. Therefore, one should retain the ice chunks. –B claims that the ice prevents the function of the refrigerator since it covers the cooling pipes. Who is right? -10C -25C -10C k=205 W/mK k=1.6 W/mK, c=2100 J/kgK
Linear thermal expansion T 0, L 0 LL T, L See table 12.2
Pontchartrain Causeway Lake Pontchartrain is a large shallow brackish lake bordering New Orleans to the north. A 23- mile causeway bridge is leading over the lake. The temperatures in winter drop to about 35 F, while in summer the surface temperature of the bridge easily surpasses 120 F. Estimate the length difference of this concrete causeway between winter and summer.
Volume expansion Relation between volume expansion coefficient and linear expansion coefficient?
Causes of thermal expansion? x Potential energy of bond Distance between two particles Spring-like bonds Equilibrium distance Realistic bonds Equilibrium distance Asymmetric binding energy results in thermal expansion of solids
Behavior of gases Consider a cylinder filled with air. A piston is slowly being pushed to the left. Assume, the gas is in thermal equilibrium with its surroundings. When the volume of gas will become smaller, will the pressure 1 increase? 2 decrease? 3 stay the same? 290 K Boyle’s Law Isothermal process
Behavior of gases Consider the same cylinder. The piston is free to move without friction (p=const). A flame is slowly heating the air inside. When the temperature of the air increases, will the volume 1 increase? 2 decrease? 3 stay the same? P=1atm Charles’ Law Isobaric process
Behavior of gases Consider the same cylinder. The piston is fixed (V=const). A flame is slowly heating the air inside. When the temperature of the air increases, will the pressure 1 increase? 2 decrease? 3 stay the same? Gay-Lussac’s Law Isochoric process
Ideal gas law How many kg of air would we find in the auditorium at this time? D=1.23 kg/m 3