I just sent this to all students in the PHY 122/PHY 124 email list. Look at that email to get the jpg attachment of the figure described below.
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Attached to this email is a jpg picture file of a screenshot I made of Fig. 22.14 in SV8. It shows graphs of n vs. wavelength lambda in nm for three different materials. One of these, acrylic (plastic), is the material used to make the prism you'll be using in Part I of Lab 6. Even though the the Lab 6 manual labels Part I.3 "Dispersion: qualitative only", you should try to be as quantitative as possible. This week's WebAssign HW problem 5 (which is SV8, Ch. 22, Prob. 32) is a quantitative problem on dispersion in a prism. You can use it as the basis for understanding Lab 6 Part I.3 in a more quantitative way. For this you'll need the dispersion curve for acrylic (plastic) in the attached Fig. 22.14.
Prof. Koch
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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
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