1. Announcements 9/15/10 There still are students with unregistered clickers. Here are the students who didn’t get any points for either of the last two clicker quizzes. If you were here and did the quizzes, that means your clickers are not registered. (Sorry to name names.) a. a.Liz Anderson b. b.Michael Collins c. c.Colin Fluckiger d. d.Cody Heffner e. e.Brian Jackson f. f.Matthew Matheson g. g.Jacob Peary h. h.Christopher Read

2. The fact that desert sand is very hot in the day and very cold at night is evidence that sand has a: a. a.low specific heat b. b.high specific heat Thought question

3. Quick Writing: Ralph's professor stated "If you add an ice cube to a glass of water, the temperature of the water does not necessarily decrease." That seems bizarre to him, because ice is obviously used to cool down water! Can you help him understand why his professor’s comment is true? a. a.Hint: What happens if you add ice to 0  C water?

4. Reading quiz (graded) Which of the following is not a way heat can be transferred? a. a.conduction b. b.convection c. c.perpetuation d. d.radiation

5. Reading quiz (graded) Which of the following does not continuously emit electromagnetic waves? a. a.A light bulb which is turned on b. b.A light bulb which is turned off c. c.A neutron star d. d.An ice cube e. e.None of the above

6. Blackbody Radiation Hot objects glow! a. a.That glow carries away energy Surroundings also glow! a. a.That glow adds energy

7. Demo Burning ants with magnifying glass a. a.OK, not really

8. Color of emission You’ll learn/derive the equation in Phys 360, if you take it. Area ~ T 4

9. More on Emissivity “Fudge factor” between 0 and 1 Different for different surfaces a. a.0.05 for “highly polished aluminum” b. b.0.8 for “anodized aluminum” Same as “absorptivity” a. a.Why? Different for different wavelengths a. a.Greenhouse effect

10. A metal sphere is heated to 1200 K, and puts out 1000 W of radiation energy. If it is cooled to 600 K, it will put out ______ W of radiation energy. (Don’t worry about heat absorbed by surroundings. Assume emissivity is the same for the two temperatures.) a. a.31.25 b. b.62.5 c. c.125 d. d.250 e. e.500 Thought question

11. Reading quiz (graded) The rate that heat is conducted through a wall (temperature T 1 on one side, T 2 on other side) is proportional to… a. a.T 2 -T 1 b. b.(T 2 -T 1 ) 2 c. c.(T 2 -T 1 ) 1/2 d. d.log(T 2 -T 1 ) e. e.exp(T 2 -T 1 )

12. Thermal Conduction A T 2 hot T 1 cold L Really:

13. Thought question If I heat one end of an iron rod such that its temperature is a constant 150 degrees C, and I put the other end in ice water, what will the temperature of the middle of the rod when the rod approaches “steady state”? a. a.0 ºC ≤ T < 50 ºC b. b.50 ºC ≤ T < 75 ºC c. c.75 ºC ≤ T < 100 ºC d. d.100 ºC ≤ T < 150 ºC e. e.T = 150 ºC “Steady state” vs. “Thermal equilibrium”

14. Thermal Conductivity Some Thermal Conductivities (from your textbook) Materialk (J/s∙m∙  C) Copper397 Aluminum238 Iron79.5 Glass0.84 Wood0.10 Air0.0234

15. Thought Question You put the end of a rod in a fire and the other end in a tub of water. The rod that would heat the water fastest will be: a. a.short and fat b. b.long and fat c. c.short and thin d. d.long and thin

16. Thought question: If I heat one end of an iron rod to 150 degrees C and I put the other end in ice water, I get a heat flow of 10 J/s through it. If I do the same with a particular copper rod, I get 25 J/s. If I stick the two of them together, side by side, how much heat will flow through the combined rod? a. a.10 Watts or less b. b.More than 10 but not greater than 25 c. c.More than 25 but less than 35 d. d.35 Watts e. e.More than 35 Watts T 2 hot T 1 cold iron Cu

17. Thought question: I put an iron rod and a copper rod end-to-end to form one long rod. The total heat flow through the combined rod is 100 J/s. How does the heat flow (J/s) through the iron compare to the heat flow through the copper? (k iron = 79.5 W/m  C; k Cu = 397 W/m  C) a. a.P iron < P copper b. b.P iron > P copper c. c.P iron = P copper T 2 hot T 1 cold iron Cu

18. R-values Some R-values (from your textbook) MaterialR (ft 2  F  hr/Btu) Brick, 4” thick 4 Styrofoam, 1” thick 5 Fiberglass insulation, 3.5” thick10.9 Drywall, 0.5” thick 0.45

19. Convection Demo: dye in tube