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Phy 202
Your 'question form' report has been received. Scroll down through the document to see any comments I might have inserted, and my final comment at the end.
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I was just wondering how I know my grades for the lab exercises/open queries? When you say that it looks good or that it has good responses, is that associated with a letter grade? Or are these graded mostly on completion? I'm trying to determine if I should go back over them for revision or whether it is not necessary. I really appreciate you answering all these questions for me, thank you. And I know I had a late start to the class but I should have all the lab exercises and all the tests completed by the 29th.
@& For your course, if you complete the exercises and labs, including revisions if I request them, you pretty much get maximum credit for those parts of your grade.
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Phy 202
Your 'question form' report has been received. Scroll down through the document to see any comments I might have inserted, and my final comment at the end.
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I noticed in a note that you wanted us to tell you what grade we were aiming for, and why we are taking the class. I know this is a question form and I'm not actually asking a question but it seemed the most efficient method of communicating. I'm taking this in order to transfer the credit back into Virginia Tech, and thereby free up some credit space, as I'm a double major and need every hour I can get. Virginia Tech requires only that I get a 70 or above, because the class will be counted Pass/Fail. However, I am aiming for an A, because I actually enjoy physics and I pride myself on my schoolwork.
@& You're doing a good job, and from the work I've seen so far an A is a reasonable goal. A lot will, of course, be determined by your tests.*@
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Phy 202
Your 'question form' report has been received. Scroll down through the document to see any comments I might have inserted, and my final comment at the end.
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Examining a Bottle Engine
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In your notes you state that in order to find work from a graph of volume vs temperature of a bottle engine, you find the area under the graph. Does that mean the area formed by connected V1,P2 to V3,P3, thereby making a triangle? Or does that mean the area formed by V2,P2 and V3,P3 with the X-axis, thereby making a rectangle?
@& The area under the graph is the area of the region formed between the points (V1, 0), (V1, P1), (V2, P2) and (V2, 0).
In many case (V1, P1) and (V2, P2) are connected by a straight line. But there are also cases where it's a curve.
The two phases in this question, however, are straight lines. So the region is a rectangle, sitting on the x axis.*@
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In this example...
Analyze the pressure vs. volume of a 'bottle engine' consisting of 4 liters of an ideal gas as it operates between minimum temperature 210 Celsius and maximum temperature 330 Celsius, pumping water to half the maximum possible height. Sketch a pressure vs. volume graph from the original state to the maximum-temperature state and use the graph to determine the useful work done by the expansion.
How would work be determined? For that matter, how would the maximum height be determined? Without P1 or P2 I cannot figure out a way to discern the maximum possible height.
@& The bottle engine setup always starts from atmospheric pressure unless otherwise specified. Be sure you see the related material on the DVD's (class notes, experiments as indicated on the Assingments page).
If the pressure starts at 1 atmosphere when the temperature is 210 C, then what is the pressure when the temperature is 330 C, assuming no significant change in volume?
How high would a water column have to be in order to exert a pressure equal to the difference in these pressures?
That's the maximum possible height.
Additional questions are always welcome.*@
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Phy 202
Your 'question form' report has been received. Scroll down through the document to see any comments I might have inserted, and my final comment at the end.
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When you say a system is at atmospheric pressure, and the pressure then increases by .22atm, what does that mean? Does that mean P1 is 0 and P2 is 0.22? Does it mean P1 is 1atm and P2 is 1.22?
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@& The gas laws apply only to absolute pressures.
So the pressures would be 1 atmosphere and 1.22 atmospheres (as in your second conjecture).*@
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Phy 202
Your 'question form' report has been received. Scroll down through the document to see any comments I might have inserted, and my final comment at the end.
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I was wondering if you could tell me if my answer for a Thermodynamic problem is correct.
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The problem comes from a Practice Test:
If we add 1.6 grams of steam at 100 C to and 20 grams of ice at 0 C to 220 grams of water at 25 C, what will be the final temperature of the mixture, assuming that all thermal exchanges take place within this system? The heats of vaporization and fusion for water are about 2250 J/gram and 335 J/gram.
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So what I was I took 1.6g*2250J/gram + 4180*1.6*(100-Tf) = 20g(335J/g) + 4180*(20)(0 + Tf)... Tf = 7.37 C
and then 21.6(7.37 + Tf)(4180) = 220(25 - Tf)(4180)... Tf = 22.106
@& You need to be very careful, and very explicit, with units.
For example 4180*1.6 does not include units.
The units would be Joules / (kg Celsius) and grams.
grams / kg = .001.
Also 0 + Tf on your right-hand side should be Tf - 0. You get the same result but you need to be sure you're thinking correctly about the temperature change.
Other than this and the units issue your equation is well set up.*@