The PHY 124 Fall 2010 Lab 8 pretest is now posted for you to work on and submit before the beginning of your Lab 8 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 8 pretest consists of 4 questions. The second is worth 8 points, and the other three are worth 9 points each, making the total possible score 35 points. To do the pretest you will need to study carefully the Lab 8 manual and to re-familiarize yourself with MapleTA syntax. 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
and, finally, the
-- "PHY 124 Lab 8 - "Measurement of e/m for the electron" 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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36 comments:
number 4 is giving me alot of trouble.First of all is the actually answer supposed to be in a's and s's. also what is meant by the error const 2deltaa/a
For question 1c, I got r=((2Vm)/(B^2e))^(1/2), please tell me what did I do wrong
these quizzes are becoming increasingly mundane and really waste time
any hints for solving number 4?
is there a glitch with number 4??
I put sqrt((((Deltas)/s)^2)+(((Delta)/a)^2)) and it is not the right answer. I don't know what is wrong...
Question 1d I got (sqrt(2qV/m))/(rB) and the answer is wrong. If my algebra is correct, e/m = v/rB. When substituting v with sqrt(2qV/m), which gives the formula above, it says I am wrong. Anyone got 1d and could help, I'd really appreciate it.
Question 1d I got (sqrt(2qV/m))/(rB) and the answer is wrong. If my algebra is correct, e/m = v/rB. When substituting v with sqrt(2qV/m), which gives the formula above, it says I am wrong. Anyone got 1d and could help, I'd really appreciate it.
just plug in the formula that they provided, dont do what you are doing with the sqrt(2qV/m), v is different from the big letter V. You just plug in the formula that the pre-lab has written for e/m.
does anyone understand number 3, i get (deltar)^2/r^2, why is that not right, please help!
For question 4, i got sqrt((deltaa/a)^2+(deltas/s)^2),it does not work, please help me! Thanks.Bye.
Saira, for number 3 take S=(Ir)^2 and Ir=A when you use E8, then use E3 to get your answer in terms or Deltar/r. It's actually a lot easier than I thought it was going to be.
Has anyone figured out number 4 yet? What is "s"?? There's no s in the formula, so I don't understand where it comes from when you determine the error.
This question is so badly worded. I have read it several times and still have no idea what the starting equation is. It's not the equation we got for #1 since we're not using B, r, or V. If we use what we're given: (e/m)=slope/const (which we're not given terms for, so I'm left to assume e/m=s/a) won't "const" (a) drop out of the error because it's a constant? Correct me if I'm wrong but I thought you couldn't propagate error for a constant. Isn't that why the constant (a) drops out of Δ(aX)/aX=ΔX/X?
I understand why we do these problems most of the time. They make you have to think about what you're doing and force you to learn how to manipulate equations. With this problem however, I feel like I'm going to be spending the next hour just trying to decipher what the starting equation is which doesn't teach me anything.
still not getting 4
Those of you having trouble with number 4: At lest one of you has a typo. You're instructed to write Delta as Deltaa (the first letter of the alphabet appears twice, not once, at the end of it); it's not Delta .
The statement of the problem instructs you what the consequence is of the a-dependence in const. being a^2 (that is, a-squared). Application of (E.8) leads to the 2 in front of Deltaa/a. You must not forget that 2 in what follows in the problem.
In problem 4, s stands for the slope in the expression that appears in the statement of the problem: e/m = slope/const. Look at the first sentence of the last paragraph of the Lab 8 manual.
Thank you Professor Koch. That was really helpful:)
After reading all of the comments from students and Professor Koch, I'm still not understanding problem 4. How do you relate the slope, s, and the constant, a, to the e/m ratio? Is the answer supposed to be in terms of Deltaa and Deltas or what? I tried using equation E.7 in the UEG manual and I'm trying to understand what the manual is trying to say about s, slope and a, constant, but I'm stumped. Please help!
sqrt((Deltas/s)^2+(Deltaa/a)^2)
is not the right answer
Prof. Koch said a 2 in front of Deltaa/a.
Anonymous @ 6:01 pm: Please read carefully the last paragraph of the Lab 8 manual. There you see an equation. Think of V as "y" and (Ir)^2 as "x". Plotting V vs. (Ir)^2 is like plotting y vs. x: a standard xy plot. What is the slope of that plot? It's constant times e/m. I hope you now see how this leads to an experimental value of e/m.
Hmm okay so since
s= slope = V/(IR)^2,
a= constant
e/m = slope/constant = s/a = V/(((IR)^2)a)
how would we phrase the answer using E.7?
E.7 would give us the answer:
sqrt((Deltas/s)^2+(Deltaa/a)^2)
as John stated would it not?
But since a is a constant then according to E.3, the formula for the error would be:
Deltas/s
because the equation would essentially be e/m = s(1/a) where a is a constant. So E.3 makes the relative error of e/m = Deltas/s as stated above. But this is also not the correct answer.
I may not be interpreting the equations or variables correctly, please let me know what I am doing wrong.
This is a very unfair system, especially for the people who have the lab on Monday. The people who have the lab on Monday have to run around to find the answers for the prelab, while the people who have the lab on the later days, can simply ask their friends, who have had the lab earlier in the week for the answers.
This is a very unfair system, especially for the people who have the lab on Monday. The people who have the lab on Monday have to run around to find the answers for the prelab, while the people who have the lab on the later days, can simply ask their friends, who have had the lab earlier in the week for the answers.
For question number 3, i dont understand what I am doing wrong, since eq.3 says delta(aX)/aX=deltaX/X, so question 3, we should get delta(Ir)/Ir=deltar/r, and then if you use equation 4, we get (deltar/r)*r= deltar, what am i doing wrong, please help before 3 pm. Thanks.
problem is you have to
(2*(Deltaa/a))^2)
You have to put the paranthesis justtttt right. I had to screw with it until something stuck. I have to make my window all big just to keep track of the parenthesis. Maybe it's time for new glasses..idk
Anyone have any suggestions for how to do Question 1 (c). I tried using the equation from the textbook, and I also tried rearranging the equation given in the lab manual.
Is the answer only supposed to have m, e, and b? I don't get it.
Thanks, if anyone can help.
Anyone have any suggestions for how to do Question 1 (c). I tried using the equation from the textbook, and I also tried rearranging the equation given in the lab manual.
Is the answer only supposed to have m, e, and b? I don't get it.
ok go to section 19.6 in the book, and then use the same formula, i think the formula is something like
mv/qB ( the book has the same exact formula), just make sure you put the parenthesis and do one more easy thing, i just can't tell you anything else or the professor will think i am giving you the answer,
Saira,
Thank you! I forgot parentheses.
please helop with question number 3, I am so confused! i tried everything!
@ 10:10 am
Use equation E.8 first for question 3, it makes it much easier. hopefully that will help lead you in the right direction.
hey, for questin 3 if i use equation 8, i get I will get delta(Ir)/Ir=deltar/r, and then i use equation 3 and i get deltar. So, what am i doing wrong! Please help!
Anonymous @ 10:30 am. You wrote
"hey, for questin 3 if i use equation 8, i get I will get delta(Ir)/Ir=deltar/r, and then i use equation 3 and i get deltar. So, what am i doing wrong! Please help!
(E.3) shows you that constant factors, here I, cancel out when evaulating relative error. (E.8) shows you how to take into account exponents (called n in the formula) when evaluating relative error. In the assigned problem (evaulating the relative error in (Ir)^2 ) you have both a constant factor, the I , and you have an exponent. Using E.3 and E.8 for the relative error in (Ir)^2 does not lead to what you wrote.
Anonymous at 12:07 am:
Your post included
"...while the people who have the lab on the later days, can simply ask their friends, who have had the lab earlier in the week for the answers."
The friends who are asked are not obliged to answer such questions from their friends.
Anonymous @ 10:30 am. You wrote
"hey, for questin 3 if i use equation 8, i get I will get delta(Ir)/Ir=deltar/r, and then i use equation 3 and i get deltar. So, what am i doing wrong! Please help!
(E.3) shows you that constant factors, here I, cancel out when evaulating relative error. (E.8) shows you how to take into account exponents (called n in the formula) when evaluating relative error. In the assigned problem (evaulating the relative error in (Ir)^2 ) you have both a constant factor, the I , and you have an exponent. Using E.3 and E.8 for the relative error in (Ir)^2 does not lead to what you wrote.
Thank you so much!
Read everything but still confused on how to do # 1c #2 my numbers are a=15cm I=1amp n=130 so i got 7.8e-4 tesla but its wrong???
and #3 cmonn helppp its confusing!!!
sqrt(((Deltas)/(s))^2+(2*(Deltaa)/(a))^2)
( ͡° ͜ʖ ͡°)
2*((Deltar)/(r))
( ͡° ͜ʖ ͡°)
KE=q*V
v=sqrt((2*q*V)/m)
r=(m*v)/(e*B)
e/m=(2*V)/(B^2*r^2)
( ͡° ͜ʖ ͡°)
Stay thirsty my friends.
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