Today we will use the known line emission spectrum from Mercury atoms to calibrate a diffraction grating, and then use our calibrated grating to determine the wavelengths of emission from hydrogen atoms.
So basically, we will measure the emission spectrum from hydrogen.
Procedure.
If you have not already seen, the homework that was supposed to be due this past Friday is now due tomorrow (Tues) at midnight.
I was getting a lot of questions, which indicated to me we didn't cover a couple of things well enough. We will go over some of the questions in class tomorrow, and hopefully by the end of it you will know how to do all of the problems ...
So the exam results are in (except for a couple of you that had a reason to make it up late). You will get your exams back tomorrow.
The raw average was 70.7%, with a standard deviation of 18.5. Not to bad, but the spread was too high. I scaled the overall result to have an average of 80%, with a standard deviation of 12.5%, which makes the distribution more comparable to the last exam and a bit more fair I think. Here is what that looks like:
If we look at the average score by question, and the number that chose to respond (recall you had to pick 8 of 12 questions), it is easy to see which questions you perceived as being more difficult. Moreover, the second plot shows that your instincts were, as a whole, correct: questions perceived as more difficult (fewer people trying them) had a lower score on average.
Apparently, questions 6 and 7 were just mean. Maybe question 3 as well, but that was taken almost verbatim from the homework.
Anyway: you all did better than you think. Below is the breakdown by letter grade. Full exam solutions should be out by week's end.
A: 12
B: 11
C: 14
D: 5
F: 4
So. I've been out of town this whole time, and have not been so responsive.
I have nearly finished grading/analyzing exam II, and I will post more information later today.
I can say this already though: Relax. I am not going to fail inordinate numbers of you. The exam will be scaled if necessary, and no one is going to radically change their grade as a result of the exam. It Will be Fine.
I have just put up a set of practice problems on WebAssign ... it will not be graded, and is optional (in fact, the solutions/answers are immediately available). It is just meant as a study aid.
If you can figure out how to solve most of those problems (say, 75% of them), you will rock the exam.
There will be 10 homework bonus points to the first person to tell me in a comment to this post what is the maximum wavelength of light required to most efficiently break up a diatomic oxygen molecule. If you are the first one within 10% of the optimal wavelength for breaking up an O2 molecule, you win.
Here's the deal on exam II, which is Tuesday 6 November. Email me if you have questions ...
The exam is problem-based (no multiple choice). You will be given 12 problems, and you can choose any 8 of them to solve. All are equally weighted, simply pick the 8 you feel the best about, and solve those. No, you can't solve 10 and have me pick the 8 to grade ...
Heavy partial credit will be given -- I want to see the right idea, and the right method more than the right number.
You are allowed 2 sides of an 8.5x11 inch sheet of paper with formulas, etc, as last time.
Below is a list of the topics covered, referenced according to both the notes and the book:
Magnetism: 3 questions
Book chapter 20 (notes chapter 7)
excludes torque on current loops and permanent magnets (book 19.5, 19.10, notes 7.3.4, 7.4.1-3)
excludes derivation of B from E via relativity (notes only)
Hint: know and love the mass spectrometer.
Induction: 3 questions
Book chapter 21 (notes chapter 8)
excludes generators (book 20.5, 20.8, notes 8.6)
Hint: voltages induced by the motion of a conductor. RL circuits.
ac Circuits / EM waves: 2 questions
Book chapter 22 (notes chapter 9)
just follow the notes ... filters in particular.
excludes calculations of reactance
includes the EM spectrum, incident power absorbed due to radiation
Hint: filters, power absorbed due to radiation
Reflection/Refraction: 2 questions
Book chapter 22 (notes chapter 10)
excludes Huygens' principle (22.6 in the book, not in notes)
Hint: make sure you know homework 7 and the last quiz.
Mirrors: 2 questions
Book chapter 23 (notes chapter 11, addendum to notes found here)
Follow the latest homework questions.
Hint: make sure you know homework 7.
Suggestions
Study exam II in the course notes packet, and the homework questions relevant to these chapters.
Some hints on numbers 3-5.
Text
Explanatory figure
Additional Explanatory figure
Problems like numbers 3 and 5 would make excellent exam questions.
Problem number 4, speaking from experience, does not.
