Please excuse getting this email twice, but I thought it doesn't hurt to make sure you get the word. I've posted this announcement on the PHY 122 Blackboard site, your PHY 124 lab section Blackboard site, and I've sent it via email from both Blackboard sites.
The PHY 124 Fall 2010 Lab 6 pretest is now posted for you to work on and submit before the beginning of your Lab 6 section next week. You will find it in the Assignments content area in Blackboard for your PHY 124 Lab section. As explained in the course syllabus, each Lab pretest is worth 35 points. As you will see, the Lab 5 pretest consists of 4 questions. The first is worth 5 points, the second is worth 5 points, the third is worth 15 points, and the fourth is worth 10 points, making the total possible score 35 points. To do the pretest you will need to study carefully the Lab 6 manual and to re-familiarize yourself with MapleTA syntax, which is used in the third question. Go to
http://www.ic.sunysb.edu/class/phy122ps/labs/dokuwiki/doku.php?id=phy124off:phy124_main_page
and read the instructions there on the "main page". Please also click on and review the
-- "Instructions" link (you've seen this before)
-- "Uncertainty, Error and Graphs" link (you've seen this before, and it's important for the third questions in the Lab 6 pretest)
and, finally, the
-- "PHY 124 Lab 6 - Reflection, Refraction and Images" link.
The "red" links are not yet active, on purpose, but as the course develops they will be made active.
As you already know, the lab pretests are prepared in the "Maple TA" software environment. You may work on each assignment as many times as you wish, but the link in the Assignments section of Blackboard for your PHY 124 section will become inactive at the starting time of your lab section. Therefore, you should not wait until just before your lab section to begin work on it. If you read the Lab Manual carefully and, there is no reason for you not to earn all 35 points for the pretest. Make sure you read carefully the instructions for each pretest problem. After each problem click on "Next" until finishing the last one, Question 4; then make sure you click on "Grade" in the Maple TA software environment. After you get your grade, you may click on "View Details" to see more about how you did. Finally, click on "Quit and Save".
Good luck!
Prof. Koch
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15 comments:
For the absolute error in 1/o, why isn't this correct:
osqrt (((Deltao/o))^2)
Isn't the relative error times o = absolute error?
First let me parse what you wrote. You have osqrt..., which means you're multiplying sqrt by o. Is that a typo? For the rest of that expression, you're taking the sqrt of something squared, which gives the "something". You're not getting what happens when you calculate the uncertainty of an inverse. For example,
(Delta(1/A))/(1/A) = (DeltaA)/A, as motivated in the pretest problem via the reference to the UEG manual. The relative uncertainty of an inverse of something is the same as the relative error of that something.
If the relative error is the same as the absolute error in this case, as you say, I did Deltao/o and that was wrong. (In the guide, it has deltax/x as the relative error).
You are asked for the absolute error in (1/o). It is correct that this is equal to the relative error in (1/o) times (1/o). The relative error in (1/o), as stated already, is equal to the relative error in o. Now just multiply it out to get the absolute error in (1/o).
Can someone please help me with number 4? I know it's probably something easy and I'm definitely making it more difficult than it should be, but I'm drawing a total blank and cannot figure out how to solve this one.
For question 3 on the prelab, I cannot seem to figure out what I am doing wrong for part 1. I did "abs(o)*(deltao)/(o) I don't understand the previous comments either about inverses. =(
Vito, look at the relative error for frequency at the bottom of the question page. Substitute o for f, and rearrange the equation.
Hi, Questio number 3, i get deltao/o^2, what am i doing wrong, please help me!
Anonymous said...
Can someone please help me with number 4? I know it's probably something easy and I'm definitely making it more difficult than it should be, but I'm drawing a total blank and cannot figure out how to solve this one.
For this problem, you have 30 cm and the f=5 cm, convert this to meters. and use the formula to find 0, which will be the answer to the shortest distance and then to find the longer distance you would have to subtract this answer by the i+o=30 cm.
And, if you got number 3 please let me know. Thanks.
A student wrote the first bit below to me, and below that is my reply:
From student: I am trying to work the MapleTA syntax on question 3 and it doesn't recognize Deltao as a triangle o. It recognizes it as the word "Deltao." I've tried many ways to go around it but there does not seem to be a way to fix this. I looked through the entire uncertainties and errors instructions and I feel that the answer should read: 1/Deltao or 1/(Deltao), which, in MapleTA should read 1/triangleo. I would very much appreciate if you can tell me if my syntax is incorrect, or if the system is just not reading the answer correctly. Thank you for your time.
My reply: When I log on on via my "student" account so that I see the same as you, I use Deltao as instructed by the statement of the problem to enter this quantity into the MapleTA-text-entry box. When I enter the correct expression in MapleTA syntax for the absolute uncertainty in (1/o), and then I click on How did I do?, the system tells me that my answer is correct. Using Deltao is correct.
Since you wrote it below with quotation marks around it, I tried using "Deltao". This is marked as incorrect.
If I use (Deltao) this is marked as correct.
I don't understand what your problem is. I suspect it is that you are not entering the correct expression for the absolute uncertainty in (1/o). The correct expression is not 1/Deltao or 1/(Deltao).
The use of the symbols Deltao or (Deltao) in the correct expression is fine. The use of "Deltao" in the expression is not.
The student wrote back:
I thank you for clearing some things up, but I think there still may be a problem.
Enter a formula in MapleTA syntax for the absolute error in 1/o in terms of (use Deltao for the absolute error in o):
-(Deltao/o)*o,reads and it is giving me the incorrect answer.
I don't know what else I can do to input the absolute error. I've looked through the UEG and tried exactly all the equations and I am not getting the correct input or answer. Sorry to keep bugging you but this question is worth a lot and it seems to be such a waste to get 25/35 for this pretest.
***************
I replied:
It is giving you the incorrect answer because it is incorrect. You have not solved the problem correctly. I cannot give you the correct answer.
Prof. Koch
is anybody getting question 3 at all?
I MIS-POSTED THIS IN THE WRONG THREAD. IT SHOULD BE ONE EARLIER IN THE THREAD BELOW.
The student wrote back to me:
I'm sorry but I've looked through the entire Uncertainty, Error and Graphs but I cannot seem to find the absolute error. I've tried these equations...
-Deltao
-Deltao/o
1/Deltao
Deltao
I am stumped on this question. Can you please explain to me how absolute error looks for this question?
I wrote to the student:
I cannot give you the correct answers to the Lab 6 pretest problems. You have to work them out, and you know you've done it when you click on the "How did I do?" link. I still don't understand what your trouble is.
Absolute uncertainty: This is defined well in UEG, and examples are given in E.1., E.4, E.6. Case E.4. is particularly useful for your trouble. You first find the relative (uncertainty) error, and then find the absolute error via E.4. The UEG calls the variable X. In your Prob. 3, first part, your X = 1/o. So the question is how to find the relative error in 1/o. The problem tells you that use of E.8 shows that the relative error in 1/o, viz., Delta(1/o)/(1/o) = Deltao/o; in this case you're using n = -1 in E.8. It follows directly. Then you use E.4.
This is essentially what I've described earlier in the blog.
I'm putting all this on the blog.
Prof. Koch
For question 3...
n = -1
relative error should look like this according to the UEG:
-1*(Deltao/o)
Then if you multiply this by 1/o, you should get the absolute error:
-1*(Deltao/o)*(1/o)
This is still not the correct answer...
What am I doing wrong here?
Yes, n = -1, but don't you see that E.8 in UEG has the absolute value symbols around the value of n. Therefore, you shouldn't have a minus sign.
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