Download Physics 2a Fall 2016 Quiz 2 To calculate your grade for this quiz

Physics 2a Fall 2016 Quiz 2 To calculate your grade for this quiz, average the values that correspond to each of the three letters you received, then multiply that by 10 to get a number out of 100: [(Individual Problem 1 + Individual Problem 2 + Group Problem 1)/3] x 10 = your grade Note that for different problems, the letters have ​
​ different values. Individual Problem 1: Q: (10/10) Fantastic work! Your Temperature vs. Energy Added diagram (also sometimes referred to as a three­phase diagram) had all the important temperatures labeled and the correct initial and final points of the H​2​O indicated. L: (10/10) Your Temperature vs. Energy Added diagram (also sometimes referred to as a three­phase diagram) had all the important temperatures labeled and the correct initial and final points of the H​2​O indicated. However, it ALSO had the initial and final temperatures for the coffee (which may or may not be correct). I didn’t grade you on the three­phase model for the coffee. In the future be careful, because if you provide more information than is being asked for, I may grade you on your reasoning as it is related to both models. R: (9.5/10) Nice work! It is clear to me that you understand what is happening with the H​2​O, but your diagram is a little unclear either because your initial and final points are not labeled as such, it’s not 100% clear that the final point is at 90ºC, or your units of temperature are not labeled. These are minor errors and therefore you are still earning an “A” for your work on this. T: (8.5/10) Your initial point is in the correct location, and your final point is in the liquid state, but you either forgot to label the final temperature, or you indicated it was something other than 90ºC. The problem states that the final temperature of the H​2​O is 90ºC. If you chose another temperature, I am interested in hearing your reasoning, because I want to make sure that I am phrasing problems in a way that makes sense. M: (8/10) You initial point for the H​2​O is correct, but for your final point, you either indicated that the final temperature was 100ºC, or you indicated that the H​2​O boiled at 90ºC. The H​2​O could not reach 100ºC, and the problem stated that the final temperature was 90ºC. We also know from class that the boiling point of water is 100ºC, so 90ºC should not be at the phase change temperature. S: (7.5/10) Oops! You made a three­phase diagram for the coffee and not the H​2​O. Your diagram for the coffee is correct, but this is not what I asked for. Please read the problem carefully and make sure that you understand what you are being asked to do. W: (7/10) Either your initial point or your final point for the H​2​O is correct, but the other is in the wrong state and/or at a phase change temperature when it should not be. Check out the possible solutions to determine which of your points is correct, and make sure you understand why. You should practice with these diagrams and bring your questions to office hours. K: (6/10) Both your initial point and your final point for the H​2​O is incorrect. Try re­working the problem again slowly outside the quiz environment, and then compare your answers with the possible solutions, and see if those answers make sense. Practice more with these diagrams and bring your questions to office hours. Group Problem 1: Q: (10/10) Awesome! Your Energy Interaction Diagram looks great and you included all the details one would need to analyze what is happening! R: (10/10) Nicely done! Your Energy Interaction Diagram tells the viewer what is happening. You did not include a timeline on your diagram. It is not necessary to include it to get all the points, but it’s a good idea to get in the habit of drawing them now because the systems will get more complicated in the future. J: (10/10) To avoid confusion during phase changes the highest (most upper right on the Temperature versus Energy Added Diagram) phase should be used. Use the mass of gas when talking about boiling/liquefying, and use the mass of liquid when talking about melting/freezing. (You may also be missing a timeline, if so, see also the feedback from category “R” for this problem.) G: (9/10) You were asked to only model the H​2​O, not coffee. You indicated that this was a closed system, and that no heat left the coffee or H2O system through this choice. This is a possibility, but it does not necessarily happen. If you are going to make an assumption that heat is not leaving the system, you should state that assumption and explain it. W: (9.5/10) Your Energy Interaction Diagram looks really good, but you didn't put the positive/negative signs on the terms of your equation. This might seem redundant now, but it’s important for when we do calculations. Since the arrows in the diagram inform you as to what to write, it should be easy for you to include them next time. H: (7/10) You made a nice Energy Interaction Diagram, but you forgot to translate the bubbles and arrows into an equation at the bottom. As you saw in FNT 4­7 this is a necessary skill to be able to solve the problems. P: (7/10) Your energy diagram is mostly correct, accept your indicators do not make sense with the situation for your Bond Energy. For example, you may have written: initial: 100% solid, final 0% liquid. However, the ice is 100% liquid at the end of the interaction. Group Problem 2: Q: (10/10) Great job! Your reasoning was sound and you were clearly thinking critically about heat, phase change, and temperature. You have very well laid out reasoning! R: (9.5/10) Your reasoning was well done, but there were some clarity issues in the language of your statement. We still understood the meaning behind your explanation, so you received most of the credit. Compare your response to the possible solution and see your instrutor if you have questions. Y: (9.5/10) Your reasoning is correct, but your conclusion is contradictory. Perhaps you misread the prompt, but you should make sure you understand the contradiction between agreeing with the statement and what your reasoning was. M: (8.5/10) Almost all correct, but Heat Capacity isn’t why the temperature remains fixed during a phase change. Now that we have talked more about Heat Capacity and Specific Heat since you took the quiz, so has your understanding of this changed? Talking about Ebond would have been useful. L: (7/10) You indicated that energy could enter the system as work. We haven’t really talked about work in class yet. However, in order to change the phase of something, you do infact need to add heat. Does knowing this change your response? K: (8/10) While temperature is a measure of thermal energy, the two are not the same. All objects have some amount of thermal energy as it is impossible to remove all the thermal energy from an object in the real world. If energy is being transferred (heat) but thermal energy is constant it would be a good time to discuss other forms of energy such as Ebond. N: (7.5/10) You have incorrectly equated thermal energy with heat. Heat is the transfer of energy across a system boundary (over time), and thermal energy is an internal property of a system at a particular time. So, heat and thermal energy are different quantities. Heat can alter the thermal energy of a system, but it could also change the bond energy and not the thermal energy. V: (7/10) “Heat Capacity” is not why the temperature remains fixed during a phase change. From your recent discussions in discussion /lab, You should now know more about Heat Capacity and Specific Heat than you did when you took the quiz, so has your understanding of this changed? X: (7/10) You provided an answer that didn’t completely respond to Felix’s idea. You indicated that there was a relationship between Bond energy and Thermal energy and that a change in one was somehow related to the other, which is not always true. (Many of you used the heat pack as an example.) You needed to discuss Kira’s question and Felix’s idea about how heat is related to phase change in order to get full credit. S: (6.5/10) Heat is not the same as temperature. Heat be transferred to a system and can affect thermal energy and that would change the temperature you measure, but heat can also affect bond energy (like during a phase change) and that won’t change the temperature (look at the level parts of the Temperature versus Energy Added diagram). Z: (6/10) Your explanation does not represent a clear line of reasoning, and you are confusing the definitions of heat, temperature and/or changes in energy. Remember that heat is the transfer of energy across a system boundary. Adding or removing heat to a system allows either phase changes or changes in thermal energy.