Physics quiz question: comparing specific heat capacity values

Physics 205A Quiz 7, fall semester 2019
Cuesta College, San Luis Obispo, CA

A 0.25 kg glass sample (400 K initial temperature) and a 0.75 kg graphite sample (300 K initial temperature) are brought in contact with each other to reach thermal equilibrium with a final temperature of 330 K. Ignore heat exchanged with the environment. The specific heat capacity values of these two substances are not known. The __________ sample has the larger specific heat capacity value.
(A) glass.
(B) graphite.
(C) (There is a tie.)
(D) (Not enough information is given.)

Correct answer (highlight to unhide): (A)

The transfer/balance energy conservation equation for this system is given by:

Q_ext = ∆E_glass + ∆E_graphite,

and since there is no heat exchanged with the environment, Q_ext = 0, such that:

0 = m_glass·c_glass·ΔT_glass + m_graphite·c_graphite·ΔT_graphite,

and:

–m_glass·c_glass·ΔT_glass = m_graphite·c_graphite·ΔT_graphite,

–(0.25 kg)·c_glass·(–70 K) = (0.75 kg)·c_graphite·(+30 K),

(17.6 kg·K)·c_glass = (22.5 kg·K)·c_graphite.

From inspection, for the equality to hold, c_glass > c_graphite, and thus glass must have a greater specific heat capacity value than graphite.

Sections 70854, 70855
Exam code: quiz07VlnC
(A) : 25 students
(B) : 17 students
(C) : 3 students
(D) : 6 students

Success level: 49%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.82

Physics quiz archive: temperature, thermal equilibrium, heat transfers

Physics 205A Quiz 7, fall semester 2019
Cuesta College, San Luis Obispo, CA
Sections 70854, 70855
Exam code: quiz07VlnC



Sections 70854, 70855 results

0- 6 :	* [low = 3]
7-12 :	**********
13-18 :	**************
19-24 :	******************* [mean = 18.9 +/- 6.2]
25-30 :	******* [high = 30]

Online reading assignment: internal energy conservation

Physics 205A, fall semester 2019
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 internal energy conservation.


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.

"Heat is a form of energy in the atoms and molecules of a substance or material, and that originates in the internal energy of a hot substance before flowing into a cold substance. I also understand that greater masses of materials require a greater amount of heat to fulfill their heat capacity in order to change its temperature."

"Internal thermal energy is the energy of an object on the inside of the object. Also temperature is a factor that plays into internal thermal energy; the higher the temperature, the more internal thermal energy there is."

"The effect that heat has on an object's thermal energy. As an object such as when meat has ice cubes put on it, it loses thermal energy; while when the meat is being cooked it gains thermal energy."

"That heat is a transfer of energy in joules, and because of this an object cannot 'have' heat. I also understand that heat flows from hot to cold; therefore, that heat comes from (or goes to) the internal energy of a substance."

"Internal energy conservation is a half-step away from our previous discussion of mechanical energy conservation in which we establish an equation and define which terms are increasing or decreasing. This transfer/balance equation is pivotal in discerning thermal internal energy changes."

"Objects with a higher internal thermal energy transfer that energy to objects with lower internal thermal energy. Heat refers to the transfer of thermal energy, while internal thermal energy refers to the temperature of an object."

"I understood what ∆E_therm is and why we calculate that instead of just E_therm."

"I understand that Q = m·c·∆T and that can be broken down as Q_ext = ∆E_{therm, 1} + ∆E_{therm, 1}. This is a transfer/balance equation, thus one side of the individual ∆E_therm terms must increase and the other must decrease (if Q_ext = 0)."

"I don't understand anything."

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 that the equation Q = m·c·∆T and the heat units other than the joule were confusing. I was not sure how to use them in a problem."

"I am a little confused on how to apply the specific heat equation to problems. How similar is this equation to calculating specific heat in chemistry? Are the units also the same as in chemistry, such as temperature always being measured in kelvins?"

"Identifying the different amounts of lost or gained internal thermal energy of objects. I understand that some objects lose energy and some gain energy but I do not understand how to find exactly how much is lost or gained."

"What I found confusing in the presentation preview was the transfer/balance equation. This confused me at first but then I realized that if the Q external energy transfer is equal to zero (if no heat is exchanged with the environment) then the changes in thermal energies of the objects add up to zero."

"Just need some practice on heat transfers. the transfer-balance equation should help."

"What is specific heat capacity?"

"In a calorimeter, it confuses me what loses energy and what gains energy. How can we tell what materials heat is flowing between and in what direction?"

"Something I didn't understand was some parts of the heat and internal energy. I don't understand the correlation of molecular kinetic energy with internal energy."

"There are a lot of concepts that are similar and I get them mixed up, heat, hot, temperature all sound the same to me, and the internal energy seems similar too."

"I remember this equation from chemistry and it ruined my grades. The individual problems were extremely confusing and I never knew which parts were given and which were not."

"I don't think I have any yet. I'll see when you explain it in class then I'll probably be confused."

"I understood all the topics in this reading assignment."

"I'm confused on everything."

"What I don't understand is if what is subtracted from what in ∆T. That is all I really need to go over."

"I don't understand what is occurring when cooking with the salt block. I was also lost when/what is doing work when there is a change in thermal energy."

"I didn't find anything confusing--just really want to try the salt block seafood now :)"

Two objects that are brought into contact with each other will reach thermal equilibrium when they have the same:

internal energy.	*************** [15]
temperature.	************** [14]
(Both of the above choices.)	************ [12]
(Neither of the above choices.)	* [1]
(Unsure/lost/guessing/help!)	*** [3]

Raw seafood is placed on a block of salt that has already been heated up. The energy contained in the high-temperature block of salt is then transferred to the seafood, cooking it. While it is being cooked, the internal thermal energy of the seafood __________, while the thermal internal energy of the salt block __________.

increases; decreases.	**************************************** [40]
decreases; increases.	[0]
does not change; does not change.	* [1]
(Unsure/lost/guessing/help!)	**** [4]

For the seafood cooking on the salt block (ignoring heat transfers with the environment), the object that experienced the greatest amount of change (increase or decrease) in thermal internal energy was the:

seafood.	************ [12]
salt block.	** [2]
(There is a tie.)	************************* [25]
(Unsure/lost/guessing/help!)	****** [6]

Frozen meat is placed in a water bath, in order to defrost it. At the very start of this defrosting process (where the frozen meat just begins to warm up from its below-freezing temperature, and the ice crystals inside have not yet reached the melting point), the internal thermal energy of the meat __________, while the thermal internal energy of the water __________.

increases; decreases.	********************************** [34]
decreases; increases.	****** [6]
does not change; does not change.	[0]
(Unsure/lost/guessing/help!)	***** [5]

For the frozen meat in the water bath (ignoring heat transfers with the environment), the object that experienced the greatest amount of change (increase or decrease) in thermal internal energy was the:

frozen meat.	****** [6]
water bath.	******* [7]
(There is a tie.)	************************** [26]
(Unsure/lost/guessing/help!)	****** [6]

A shot of whiskey is mixed with a pint of beer to make a boilermaker. Assuming that the whiskey and beer have approximately the same temperature before they are mixed together, the internal thermal energy of the whiskey __________, while the thermal internal energy of the beer __________.

increases; decreases.	** [2]
decreases; increases.	****** [6]
does not change; does not change.	********************************* [33]
(Unsure/lost/guessing/help!)	**** [4]

For the shot of whiskey being mixed with the pint of beer (ignoring heat transfers with the environment), the object that experienced the greatest amount of change (increase or decrease) in thermal internal energy was the:

shot of whiskey.	*** [3]
pint of beer.	***** [5]
(There is a tie.)	********************************* [33]
(Unsure/lost/guessing/help!)	**** [4]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"Are there real life situations in which external conditions do not affect the thermal temperatures of the subjects?" (Stuff in a well-insulated cooler.)

"Seems straightforward."

"The transfers confuse me a lot unfortunately."

"Some of this heat stuff seems like it can be counterintuitive."

"How do we handle cases when there is heat exchanged between the system and the environment?" (In the transfer-balance equation, then you have a non-zero term for heat on the left-hand side of the equation, similar to non-conservative work being non-zero on the left-hand size of the equation for mechanical energy conservation.)

"If two objects come into contact with each other and have the same internal temperature, is there no change in internal energy?" (Correct.)

"Whiskey should never ruin a good beer."

"BBQ or sous-vide steak?"

"I'm just hungry really."

"I really want an 'A' in this class but that's not happening :/"

"I'm sorry I am super-sick."

Physics quiz question: comparing temperature changes

Physics 205A Quiz 7, fall semester 2018
Cuesta College, San Luis Obispo, CA

A 0.50 kg iron sample (600 K initial temperature) and a 0.75 kg iron sample (300 K initial temperature) are brought in contact with each other to reach thermal equilibrium. Ignore heat exchanged with the environment. Specific heat of iron is 452 J/(kg·K). After thermal equilibrium is reached, the __________ iron sample will have experienced the larger change (increase/decrease) in temperature. (A) 0.50 kg.
(B) 0.75 kg.
(C) (There is a tie.)
(D) (Not enough information is given.)

Correct answer (highlight to unhide): (A)

The transfer/balance energy conservation equation for this system is given by:

Q_ext = ∆E_{0.50 kg} + ∆E_{0.75 kg},

and since there is no heat exchanged with the environment, Q_ext = 0, such that:

0 = m_{0.50 kg}·c_iron·ΔT_{0.50 kg} + m_{0.75 kg}·c_iron·ΔT_{0.75 kg},

and:

–m_{0.50 kg}·ΔT_{0.50 kg} = m_{0.75 kg}·ΔT_{0.75 kg}.

From inspection, since m_{0.50 kg} < m_{0.75 kg}, then –ΔT_{0.50 kg} > ΔT_{0.75 kg}, and thus the 0.50 kg iron sample will under a larger temperature change (which would be a decrease in temperature) than the 0.75 kg iron sample (which would increase in temperature).

Sections 70854, 70855
Exam code: quiz07PeA7
(A) : 28 students
(B) : 3 students
(C) : 19 students
(D) : 0 students

Success level: 56%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.72

Physics quiz archive: temperature, thermal equilibrium, heat transfers

Physics 205A Quiz 7, fall semester 2018
Cuesta College, San Luis Obispo, CA
Sections 70854, 70855, version 1
Exam code: quiz07PeA7



Sections 70854, 70855 results

0- 6 :	** [low = 6]
7-12 :	****
13-18 :	***********
19-24 :	********************** [mean = 20.8 +/- 6.0]
25-30 :	************ [high = 30]

Online reading assignment: internal energy conservation

Physics 205A, fall semester 2018
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 internal energy conservation.


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 heat and internal energy and that heat tends to flow from a hotter temperature object to a lower temperature object."

"If something's thermal energy increases, the temperature increases. If the thermal energy decreases, the temperature decreases."

"I understood a lot because I learned this in chemistry. Heat always flows from high to low, if the environment has no effect then each energy term must directly mirror the other..."

"If the thermal energy of a system is increasing (heating), that means external heat is positive and is adding into the system. If it's decreasing (cooling), external heat is negative and it's removing from the system. Zero means no energy is being transferred in or out of the thermal internal energy system."

"Thermal internal energy depends on temperature. It makes sense that a low temperature object has low thermal internal energy, and a higher temperature indicates higher thermal internal energy. Energy not transferred in/out of the thermal internal energy of a system is isolated from the environment and heat exchange between the system and the external environment is zero."

"Thermal energy is transmittable between objects in the form of heat. Temperature changes are a direct result transferences of proportionate amounts of thermal energy. It is also worth noting that different materials are able to retain and transfer thermal energy very differently."

"I understand that when we look at thermal internal energy we are more focused on the change in temperature of an object or objects. Everything has its own specific heat capacity similar to last chapter when we were talking about the Young's modulus. Heat is added to a system or taken away from a system and that energy is conserved in thermally isolated areas. However, perfect thermally isolated areas do not appear often in the natural environment but we can create those in things like a thermos (still not perfect)."

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 don't understand how internal energy and temperature relate to each other."

"I understand the heat and energy concepts. I am confused about using the equations. I will pay attention in class and keep on visiting the tutors."

"New symbols/terms for these things are going to take some getting used to."

"Simple concepts in this reading. Not too much that is confusing."

"Nothing too confusing from this reading thus far."

Two objects that are brought into contact with each other will reach thermal equilibrium when they have the same:

internal energy.	******** [8]
temperature.	*************** [15]
(Both of the above choices.)	************* [13]
(Neither of the above choices.)	[0]
(Unsure/lost/guessing/help!)	*** [3]

Raw seafood is placed on a block of salt that has already been heated up. The energy contained in the high-temperature block of salt is then transferred to the seafood, cooking it. While it is being cooked, the internal thermal energy of the seafood __________, while the thermal internal energy of the salt block __________.

increases; decreases.	************************************ [36]
decreases; increases.	* [1]
does not change; does not change.	* [1]
(Unsure/lost/guessing/help!)	* [1]

For the seafood cooking on the salt block (ignoring heat transfers with the environment), the object that experienced the greatest amount of change (increase or decrease) in thermal internal energy was the:

seafood.	************* [13]
salt block.	* [1]
(There is a tie.)	*************************** [22]
(Unsure/lost/guessing/help!)	*** [3]

Frozen meat is placed in a water bath, in order to defrost it. At the very start of this defrosting process (where the frozen meat just begins to warm up from its below-freezing temperature, and the ice crystals inside have not yet reached the melting point), the internal thermal energy of the meat __________, while the thermal internal energy of the water __________.

increases; decreases.	******************************* [31]
decreases; increases.	** [2]
does not change; does not change.	**** [4]
(Unsure/lost/guessing/help!)	** [2]

For the frozen meat in the water bath (ignoring heat transfers with the environment), the object that experienced the greatest amount of change (increase or decrease) in thermal internal energy was the:

frozen meat.	******** [8]
water bath.	******* [7]
(There is a tie.)	********************* [21]
(Unsure/lost/guessing/help!)	*** [3]

A shot of whiskey is mixed with a pint of beer to make a boilermaker. Assuming that the whiskey and beer have approximately the same temperature before they are mixed together, the internal thermal energy of the whiskey __________, while the thermal internal energy of the beer __________.

increases; decreases.	[0]
decreases; increases.	* [1]
does not change; does not change.	************************************ [36]
(Unsure/lost/guessing/help!)	** [2]

For the shot of whiskey being mixed with the pint of beer (ignoring heat transfers with the environment), the object that experienced the greatest amount of change (increase or decrease) in thermal internal energy was the:

shot of whiskey.	* [1]
pint of beer.	** [2]
(There is a tie.)	********************************* [33]
(Unsure/lost/guessing/help!)	*** [3]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"I'm pretty sure that the salt block and seafood experience the same amount of change in internal energy, but if the salt block is bigger in size than the seafood that is being placed on it or if the difference in temperature is extreme (the salt block is fresh out of the oven and the seafood is frozen), wouldn't the seafood experience a greater change in internal thermal energy than the seafood? Also wouldn't the salt block have the least amount of change due to the fact that it is has more mass than the seafood?" (Yes, both the salt block and the seafood would experience the same amount of change--if the seafood gains 10,000 J, then the salt block must have lost 10,000 J (if we can neglect heat exchanged with the environment). Even if the salt block and seafood temperatures are very different, they will still undergo the same decrease/increase in internal energy. However, due to their different masses and different heat capacities, they will experience different temperature changes; typically the salt block will only "cool down a little" (experience a small temperature decrease) while the seafood will "heat up a lot" (experience a large temperature increase) despite experiencing the same amount of change (decrease/increase) in internal energy.)

"I am not exactly sure about whiskey-beer questions. If both have the same temperature prior to mixing, then there should not be a change in their thermal internal energies?" (Yes.)

"I understand that the change in thermal energies is equal for two objects interacting (only with each other, and not with the environment) and have reached thermal equilibrium. But does that mean they should have the same final temperature?" (Yes, the definition of thermal equilibrium means that the two objects have the same final temperature. Since heat flows from a hotter object to a cooler object, once the two objects have reached the same final temperature, then the exchange of heat stops.)

"Thermal energy transfers happen all around us everyday!"

"I never thought I'd see Q = m·c·ΔT outside of chemistry :/" (We're going over it here in physics, because I don't think chemistry truly covers the nuances of that equation.)

"Hope you had a great Thanksgiving?" (Eh, it was okay. I'm fine with okay; for me okay is pretty awesome. How was your Thanksgiving?)

Physics quiz question: comparing final temperatures

Physics 205A Quiz 7, fall semester 2017
Cuesta College, San Luis Obispo, CA

An aluminum sample and an iron sample have the same mass and same initial temperature, and are kept separated from each other. Specific heat of aluminum is 900 J/(kg·K); specific heat of iron is 452 J/(kg·K). If the same amount of heat is transferred to each sample, the __________ sample will have a higher final temperature.
(A) aluminum.
(B) iron.
(C) (There is a tie.)
(D) (Not enough information is given.)

Correct answer (highlight to unhide): (B)

The transfer/balance energy conservation equation for each of these systems are given by:

Q_ext = ∆E_aluminum = m_aluminum·c_aluminum·ΔT_aluminum,

and:

Q_ext = ∆E_iron = m_iron·c_iron·ΔT_iron.

For each sample and its corresponding equation, the mass m and heat Q_ext transferred is the same, so:

Q_ext = Q_ext,

m_aluminum·c_aluminum·ΔT_aluminum = m_iron·c_iron·ΔT_iron,

c_aluminum·ΔT_aluminum = c_iron·ΔT_iron,

and since c_aluminum > c_iron, then ΔT_aluminum < ΔT_iron, and:

ΔT_aluminum < ΔT_iron,

(T_aluminum,f – T_aluminum,0) < (T_iron,f – T_iron,0),

and since both samples have the same initial temperature T_aluminum,0 = T_iron,0:

T_aluminum,f < T_iron,f,

thus the iron sample will have the higher final temperature.

Sections 70854, 70855
Exam code: quiz07Whu7
(A) : 25 students
(B) : 13 students
(C) : 4 students
(D) : 0 students

Success level: 31%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.36

Physics quiz question: comparing changes in internal energies

Physics 205A Quiz 7, fall semester 2017
Cuesta College, San Luis Obispo, CA

An aluminum sample and an iron sample have the same mass. The aluminum sample initially has a higher temperature than the iron sample, and then they are brought in contact with each other to reach thermal equilibrium. Ignore heat exchanged with the environment. Specific heat of aluminum is 900 J/(kg·K); specific heat of iron is 452 J/(kg·K). After thermal equilibrium is reached, the __________ sample will have experienced the greatest change in internal energy.
(A) aluminum.
(B) iron.
(C) (There is a tie.)
(D) (Not enough information is given.)

Correct answer (highlight to unhide): (C)

The transfer/balance energy conservation equation for this system is given by:

Q_ext = ∆E_aluminum + ∆E_iron,

where for an isolated system, Q_ext = 0, so:

0 = ∆E_aluminum + ∆E_iron,

–∆E_aluminum = ∆E_iron.

This means that the aluminum sample experienced the same amount of thermal internal energy change (a decrease) as the change in the thermal internal energy of the iron sample (an increase).

Sections 70854, 70855
Exam code: quiz07Whu7
(A) : 7 students
(B) : 14 students
(C) : 19 students
(D) : 2 students

Success level: 45%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.31

Physics quiz archive: temperature, thermal equilibrium, heat transfers

Physics 205A Quiz 7, fall semester 2017
Cuesta College, San Luis Obispo, CA
Sections 70854, 70855, version 1
Exam code: quiz07Whu7


Sections 70854, 70855 results

0- 6 :
7-12 :	******* [low = 9]
13-18 :	*************
19-24 :	******************* [mean = 18.9 +/- 5.4]
25-30 :	*** [high = 27]

Online reading assignment: internal energy conservation

Physics 205A, fall semester 2017
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 internal energy conservation.


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 the concepts of heating and cooling. I am a little confused on the conservation of energy and how that looks/is applied. I am also a little confused on the visual representation of heat flow."

"As molecules move closer together (condensation or freezing), potential energy decreases, or increases as they move father apart (vaporizing, melting). I understanding that heat flows from higher temperatures to cooler temperatures, and that in an insulated system, the decrease in the internal energy of one object is equal to the increase in internal energy of the object(s) it is transferring to."

"Heat is based on the movement of the atoms of an object. Fast being 'hot' and slow being 'cold.' Heat energy can be transferred between two items until they reach temperature equilibrium. Cooling down is a decrease in thermal internal energy and heating up is an increase in thermal internal energy."

"Thermal internal energy of an object depends on atom movement. So if an atom is moving faster, then the thermal internal energy must be higher. Whereas if the thermal internal energy is lower, the atoms move much slower if at all. "

"I understand that if you ignore external factors, much like our other energy transfer equations, you may zero out the left side of the equation."

"This section is just a review for me because I have taken chemistry where we have covered internal energy conservation and the multiple ways to find it."

"I understand the concepts of heating and cooling. I am a little confused on the conservation of energy and how that looks/is applied. I am also a little confused on the visual representation of heat flow."

"The systems are in thermal equilibrium if no heat flows between them when they are connected by a path permeable to heat. Thermal equilibrium obeys the zeroth law of equilibrium."

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 just covered this material with a student that I am tutoring for general chemistry so thermochemistry is all very fresh!"

"All and all it made sense. I took chemistry last semester so this stuff is very similar to what I have learned."

"This seems straightforward so far. Unsure of the exact relationship between temperature and thermal energy, though."

"Thermal energies can find equilibrium with the objects that it interacts with. How can we find the point of equilibrium between multiple objects?"

"I find the transfer of internal energy a little confusing. I could use some review on thermal energy vs. heat."

"I have a small issue in the difference between in temperature and internal energy and how they're related."

"I do not understand the equations given in this section. Like always, I will review more before class and then come in prepared."

"Honestly there wasn't a lot I didn't understand since I've seen this before."

Two objects that are brought into contact with each other will reach thermal equilibrium when they have the same:

internal energy.	*********** [11]
temperature.	************* [13]
(Both of the above choices.)	************** [14]
(Neither of the above choices.)	[0]
(Unsure/lost/guessing/help!)	** [2]

Raw seafood is placed on a block of salt that has already been heated up. The energy contained in the high-temperature block of salt is then transferred to the seafood, cooking it. While it is being cooked, the internal thermal energy of the seafood __________, while the thermal internal energy of the salt block __________.

increases; decreases.	*********************************** [35]
decreases; increases.	*** [3]
does not change; does not change.	* [1]
(Unsure/lost/guessing/help!)	* [1]

For the seafood cooking on the salt block (ignoring heat transfers with the environment), the object that experienced the greatest amount of change (increase or decrease) in thermal internal energy was the:

seafood.	************** [14]
salt block.	***** [5]
(There is a tie.)	******************* [19]
(Unsure/lost/guessing/help!)	** [2]

Frozen meat is placed in a water bath, in order to defrost it. At the very start of this defrosting process (where the frozen meat just begins to warm up from its below-freezing temperature, and the ice crystals inside have not yet reached the melting point), the internal thermal energy of the meat __________, while the thermal internal energy of the water __________.

increases; decreases.	******************************* [31]
decreases; increases.	******* [7]
does not change; does not change.	* [1]
(Unsure/lost/guessing/help!)	* [1]

For the frozen meat in the water bath (ignoring heat transfers with the environment), the object that experienced the greatest amount of change (increase or decrease) in thermal internal energy was the:

frozen meat.	********** [10]
water bath.	****** [6]
(There is a tie.)	********************* [21]
(Unsure/lost/guessing/help!)	*** [3]

A shot of whiskey is mixed with a pint of beer to make a boilermaker. Assuming that the whiskey and beer have approximately the same temperature before they are mixed together, the internal thermal energy of the whiskey __________, while the thermal internal energy of the beer __________.

increases; decreases.	[0]
decreases; increases.	***** [5]
does not change; does not change.	********************************* [33]
(Unsure/lost/guessing/help!)	** [2]

For the shot of whiskey being mixed with the pint of beer (ignoring heat transfers with the environment), the object that experienced the greatest amount of change (increase or decrease) in thermal internal energy was the:

shot of whiskey.	* [1]
pint of beer.	**** [4]
(There is a tie.)	******************************* [31]
(Unsure/lost/guessing/help!)	**** [4]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"I really like all the real-life examples you put in your lecture."

"I feel like this is the physics of cooking. Very cool."

"Whiskey/beer example review."

"Can you explain the whiskey/beer example in class, specifically what happens when two things are the same temperature?"

"Not sure how the whiskey/beer thing works. Is it a chemical reaction?"

"I have nothing interesting to add at the moment."

Physics quiz question: equally-heated aluminum samples

Physics 205A Quiz 7, fall semester 2016
Cuesta College, San Luis Obispo, CA

"Aluminum Cube"
Cliff Hutson
flic.kr/p/rzdiCW

Two aluminum samples (0.50 kg and 0.75 kg) at 15.0° C are each separately given 15,000 J of heat. The two samples are then brought in contact with each other, and allowed to reach thermal equilibrium. Ignore heat exchanged with the environment. Specific heat of aluminum is 900 J/(kg·K). While reaching thermal equilibrium when brought in contact with each other (after each has separately been given 15,000 J of heat), heat flows from the __________ aluminum sample to the __________ aluminum sample.
(A) 0.50 kg; 0.75 kg.
(B) 0.75 kg; 0.50 kg.
(C) (No heat is exchanged.)
(D) (Not enough information is given.)

Correct answer (highlight to unhide): (A)

The transfer/balance energy conservation equation for each block is given by:

Q_ext = ∆E_small = m_small·c_Al·∆T_small,

Q_ext = ∆E_big = m_big·c_Al·∆T_big.

Since both blocks have been given the same amount of heat Q_ext = +15,000 (the positive sign denoting thermal energy added into the block) and the same specific heat c_Al, then the smaller 0.50 kg block will experience a greater increase in temperature, and be at a higher temperature than the 0.75 kg block after both have been heated up.

Thus when these two blocks are subsequently brought in contact with each other, then since the smaller 0.50 kg block is at a higher temperature than the 0.75 kg block, heat will then flow from the 0.50 kg block to the 0.75 kg block.

Sections 70854, 70855, 73320
Exam code: quiz07p4sT
(A) : 30 students
(B) : 14 students
(C) : 8 students
(D) : 0 students

Success level: 58%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.93

Physics quiz archive: temperature, thermal equilibrium, heat transfer

Physics 205A Quiz 7, fall semester 2016
Cuesta College, San Luis Obispo, CA
Sections 70854, 70855, 73320, version 1
Exam code: quiz07p4sT



Sections 70854, 70855, 73320 results

0- 6 :	* [low = 6]
7-12 :	*************
13-18 :	***************
19-24 :	*************** [mean = 18.5 +/- 6.6]
25-30 :	******** [high = 30]

Online reading assignment: internal energy conservation

Physics 205A, fall semester 2016
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 internal energy conservation.


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.

"It is not correct to say that a substance contains heat. The substance contains internal energy. Heat is the energy transfer from hot to cold."

"I somewhat understand thermal internal energy and how it is evaluated by the movement of microscopic atoms."

"I understood the equation Q = m·c·∆T as something I have done in chemistry. It is interesting now in physics."

"A low temperature object has little thermal internal energy and a high temperature object has more thermal internal energy. If temperature increases, heat from the environment is being transferred to the object and thermal internal energy increases. The opposite occurs when an object is cooled and transfers heat from the object to the environment. A system with Q = 0 is insulated from the envirnonment and there is no transfor of heat."

"I understand how to plug in things into the equation Q = m·c·∆T."

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.

"What is our definition of the system that we are working with? I know there are many types of them, could we go over the language of how to describe what is happening in a system?"

"I don't understand how to figure out which object loses more internal energy."

"Still a little bit fuzzy how this relates to mechanical energy and work."

"I'm feeling good on this material so far."

"Not much was confusing, would maybe help just going over an example of calorimetry."

Two objects that are brought into contact with each other will reach thermal equilibrium when they have the same:

internal energy.	****** [6]
temperature.	********** [10]
(Both of the above choices.)	********** [15]
(Neither of the above choices.)	* [1]
(Unsure/lost/guessing/help!)	** [2]

Raw seafood is placed on a block of salt that has already been heated up. The energy contained in the high-temperature block of salt is then transferred to the seafood, cooking it. While it is being cooked, the internal thermal energy of the seafood __________, while the thermal internal energy of the salt block __________.

increases; decreases.	******************************** [32]
decreases; increases.	* [1]
does not change; does not change.	[0]
(Unsure/lost/guessing/help!)	* [1]

For the seafood cooking on the salt block (ignoring heat transfers with the environment), the object that experienced the greatest amount of change (increase or decrease) in thermal internal energy was the:

seafood.	********** [10]
salt block.	***** [5]
(There is a tie.)	****************** [18]
(Unsure/lost/guessing/help!)	* [1]

Frozen meat is placed in a water bath, in order to defrost it. At the very start of this defrosting process (where the frozen meat just begins to warm up from its below-freezing temperature, and the ice crystals inside have not yet reached the melting point), the internal thermal energy of the meat __________, while the thermal internal energy of the water __________.

increases; decreases.	********************** [22]
decreases; increases.	******* [7]
does not change; does not change.	**** [4]
(Unsure/lost/guessing/help!)	* [1]

For the frozen meat in the water bath (ignoring heat transfers with the environment), the object that experienced the greatest amount of change (increase or decrease) in thermal internal energy was the:

frozen meat.	**** [4]
water bath.	******* [7]
(There is a tie.)	******************** [20]
(Unsure/lost/guessing/help!)	*** [3]

A shot of whiskey is mixed with a pint of beer to make a boilermaker. Assuming that the whiskey and beer have approximately the same temperature before they are mixed together, the internal thermal energy of the whiskey __________, while the thermal internal energy of the beer __________.

increases; decreases.	* [1]
decreases; increases.	* [1]
does not change; does not change.	****************************** [30]
(Unsure/lost/guessing/help!)	** [2]

For the shot of whiskey being mixed with the pint of beer (ignoring heat transfers with the environment), the object that experienced the greatest amount of change (increase or decrease) in thermal internal energy was the:

shot of whiskey.	[0]
pint of beer.	** [2]
(There is a tie.)	***************************** [29]
(Unsure/lost/guessing/help!)	*** [3]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"I am confused with heat transfers between internal energy systems and when there may be a tie or not." (If there are only two internal energy systems that interact, then the amount they change will be a tie (one will be an increase, the other a decrease) as long as there are no third parties: one or more other internal energy systems, and/or heat losses/gains from the environment.)

"Why are we measuring temperature in kelvin?" (When we're doing chemistry, we do as chemists physicists do.)

"I observed three candles burning side by side. The candle in the center melted much faster than the two outer candles. What is the energy transfer relationship taking place?" (Radiative heat transfer!)

"Wouldn't the salt block have experienced the greatest changes in energy because it is heated up then losing heat from it transferring to the seafood?" (Perhaps, but the process of interest is after it is heated up, and the seafood is placed on it. Also, if the process is heating up the salt block, then it loses heat, the net change in internal energy wouldn't be very much.)

"Can we use the same technique for finding non-conservative energy loss for internal thermal energies as we did with mechanical energy forms?" (Yes. The transfer-balance equation, but with heat instead of work, and internal energy changes instead of mechanical energy changes.)

I'm slightly confused at the concept of heat flow. Why does the hotter object give off thermal heat to the colder object? It makes sense but I would like to know the chemical reason for this transfer of energy." (It has something to do with entropy, but even in collisions in cars we've seen how a faster car can transfer some of that translational kinetic energy to a slower car. Similarly for ideal gases, a faster (higher temperature atom) will transfer some of its internal energy to a slower (lower temperature) atom.)

"Will there be any more extra credit opportunities before the final?" (I'll look into it. But be sure to maximize the regular points remaining in this semester.)