Cuesta College, San Luis Obispo, CA
Students have a weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.
The following questions were asked on reading textbook chapters and previewing a presentation on heat transfers.
Selected/edited responses are given below.
Describe something you found interesting from the assigned textbook reading or presentation preview, and explain why this was personally interesting for you.
"I think that Space Shuttle tiles are the coolest thing in the world."
"The Cooper Cooler™ kind of makes sense. The aluminum can has a pretty high thermal conductivity, so that will increase the amount of heat from the can to the ice. The soda is in a closed system, so the heat transfer goes directly to the ice. The change in temperature is high, so the rate of heat flow will be high. The thin diameter of the can will also increase the rate of heat flow from the can to the ice. I would like to try this."
"Seeing the 'mythbusting' examples makes me excited for the next lab."
"I thought the lava lamp example was cool, it helped make the concept of convection easier to understand."
"Internal (thermal) energy depends on the product of mass, specific heat capacity and temperature."
"I found it interesting that e is different for black-bodied and silver-bodied objects."
"It had never occurred to me that because black objects were good absorbers that they therefore were also good radiators, so it was interesting to learn that and connect the dots of something that should be so obvious."
"I found it interesting that cooling food is considered to be forced convection. When we attempt to cool it by blowing on the surface, thermal energy is released.
Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"The picto-quiz examples of heat transfer was hard to evaluate which heat transfer was taking place. I hope we will go over them in class."
"I don't really understand why the temperature component of Stefan's law is to the power of 4."
"It all made sense."
"Conduction was confusing to me. I think I will need a clearer explanation in class of how changes in temperature, κ and area affect heat flow per time."
"I found Stefan's law of radiation and Wien's law confusing. I need help applying these laws."
"While it's not necessarily confusing, the material in this section definitely feels quite more advanced than what we've covered so far. The equations are just kind of thrown at us in the book, so they're a little hard to grasp immediately."
"Why does an object that is shiny radiate heat less efficiently than objects that aren't as shiny?"
In both Fourier's law of heat conduction and Stefan's law of (net) thermal radiation, briefly describe the parameter "P" ("script P") and its SI units.
"I could not figure it out."
"The rate of heat flow given in watts or J/s."
Indicate how changing these parameters of wall covered with a slab of insulating foam placed between a warm room interior and cool environment will affect the amount of energy it conducts per time. Assume all other parameters remain constant.
(Only correct responses shown.)
Replacing it with a foam slab twice as thick: decreases [70%]
Replacing it with a different material slab with a lower thermal conductivity value: decreases [56%]
Lowering the interior room temperature: decreases [54%]
In Stefan's law of (net) thermal radiation, briefly describe the parameter e and its SI units.
"e is a value from 0 to 1 and is a measure of how good a reflector or radiator/absorber it is. I do not think it has a SI unit."
Indicate how changing these parameters of reflective, shiny balloon that is much warmer than its environment will affect the amount of energy it radiates per time. Assume all other parameters remain constant.
(Only correct responses shown.)
Painting it matte black: increases [43%]
Inflating its size: increases [60%]
Lowering its temperature: decreases [65%]
Indicate how changing these parameters of reflective, shiny balloon that is much cooler than its environment will affect the amount of energy it absorbs per time. Assume all other parameters remain constant.
(Only correct responses shown.)
Painting it matte black: increases [72%]
Inflating its size: increases [52%]
Lowering its temperature: increases [26%]
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Just to clarify: conduction has to do with heat transfer between objects in some sort of contact, convection has to do with heat transfer with air currents, and radiation has to do with heat transfer by using light?" (Yes, yes, and yes.)
"So what energy transfer heats up food fastest? What about the slowest?" (Sounds like we should set up a kitchen tasting event to verify this.)
"How much energy does an object transfer when the temperature is not uniform everywhere? Is it until the same energy is everywhere?" (Not necessarily--only until there is the same temperature everywhere--i.e., thermal equilibrium is reached.)
"This entire presentation seems to be all over the place. I'm not quite sure what to do with these formulas."
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