Cuesta College, San Luis Obispo, CA
Students have a bi- 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 what you understand from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically demonstrate your level of understanding.
"I understand that the difference in colors changes the amount of radiative heat that is absorbed."
"I understand the three forms of heat transfers: conduction, convection, and radiation."
"The power through a wall is proportional to the temperature difference.As per the zeroth law of thermodynamics, heat flows from high to low temperatures!"
"Convection is the process of fluids carrying heat and conduction is heat passing directly through an object. The power of heat is stronger with a greater change in temperature and minimal resistance. Radiation is energy carried by electromagnetic waves."
"The first thing I learned is that heating chocolate bunnies is extremely funny for some reason. I also learned that convection, conduction and radiation are types of heat transfers that transport heat. Convection uses circulating air, conduction transfers through an object and radiation is in the form of light."
"There are different types of heat transfers conduction, convection and radiation. In conduction, heat is transferred through an object, e.g. when your mom says don’t touch the stove because it’s hot but you really want that mac-n-cheese and you touch it anyway and burn yourself on the stove. In convection, heat transfers with the circulation of air, e.g. old fashioned radiator it takes in cool air at the bottom and produces hot air through the top. In radiation heat is transported in the form of light, e.g. soaking in the sun on a nice beach day (I miss summer)."
"Conduction is when heat is transferred through an object; convection is when heat is circulated in the air; radiation is when heat is transferred as light."
"Insulation thickness makes it more resistant to heat. The conductivity is the opposite, transferring heat faster through the material."
"I have noted and understand the differences between convection, conduction, and radiation. Blackbodies are good absorbers and therefore are good emitters. Emissivity is a dimensionless number between 0 and 1 that is the ratio of the energy an object actually radiates to what it would radiate."
"Black absorbs; white reflects."
Describe what you found confusing from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically identify the concept(s) that you do not understand.
"I found the equations confusing."
"Fourier's law confuses me."
"I am a little confused about conductivity and how it affects thermal resistance. Im sure once its explained in class it will be much clearer."
"I haven't given myself quite enough time to figure out what exactly don't understand because everything seems a little confusing. I do think that maybe i'd like to better understand thermal resistance."
"All and all in made sense. The part that somewhat got confusing was the formulas. More specifically with the applications. What each of the variables mean."
"I found Stepfan's law more confusing. I would appreciate some review on how this works."
"Colors affecting radiative absorption?"
(Only correct responses shown.)
insulation thickness d: maximize [82%]
insulation conductivity κ: minimize [64%]
Total surface area A exposed to the outdoors: minimize [61%]
In order to minimize the amount of heat flowing per time through these exterior walls, should the following parameters be minimized, maximized (or has no effect)?
(Only correct responses shown.)
temperature difference ∆T between indoors and outdoors: minimize [63%]
thermal resistance R of the walls: maximize [72%]
black. *************************** [27] silver. **** [4] (There is a tie.) [0] (Unsure/guessing/lost/help!) ** [2]
black. ****************** [18] silver. *********** [11] (There is a tie.) ** [2] (Unsure/guessing/lost/help!) ** [2]
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Everything progressively gets more interesting. I'm excited for Physics 205B!"
"As a welder I work with heat quite a bit."
"Is the zeroth law of thermodynamic is the equilibrium of temperatures?" (Yes. Surprisingly, it is not a trivial law.)
"Does heat always flow from high temperatures to low temperatures?" (Yes, all by itself. However, if you want heat to flow from low temperatures to high temperatures (in order to cool down your refrigerator, or use air conditioning to cool down your house), then you will need to spend energy in the form of work to move heat "opposite of the way it wants to go." Also heat pumps will move heat from low temperatures to high temperatures in order to extract energy from the cool environment to heat your house, but this again requires you to spend energy in the form of work to move heat "opposite of the way it wants to go.")
"You know me just a run down of the formulas would be greatttttt." (Mmmmkay.)
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