December 3, 2017
###### Inverse Square Law:What would the slope of the line on a log plot be if brightness followed an inverse cubed law instead of an inverse squared law?
December 4, 2017

Laboratory #4

Fall 2017

Spectroscopy

1. This lab will be completed in class.
2. a) You will need to work with a lab partner.
3. b) At least one of you will need a working camera (for instance on your phone).
4. Working with your lab partner(s), go to blackboard and complete the pre-lab assessment for Lab #4. a) First complete the test using your account.
5. b) Once you are finished, log out, let your lab partner log in, and repeat the test so that each person has completed it.
6. Once each of you has completed the assessment, begin the lab.
7. a) Get a diffraction grating from your instructor.
8. b) Around the room there are five long thin light bulbs.
9. c) These are called “spectral tubes”.
10. d) Four of them are labeled with the gas they contain; The fifth is not.
11. e) It will be your job to determine the gas in the fifth tube.
12. Record a spectrum of each tube.
13. a) Hold the diffraction grating against the front of the lens of the camera with the writing upright.
14. b) Point the camera at the tube.
15. c) You will see an image of the tube. d) Now rotate the camera to point to the side of the tube (about 45 degrees).
16. e) You will see a series of bright lines. That is the spectrum of the gas.
17. f) The image will be clearer if your lab partner holds a blank sheet of paper as a back drop and blocks out any stray light.
18. g) Keep track of which spectrum goes with which tube.
19. h) Make a note of the color of each bulb.
20. i) Repeat this procedure until you have a clear spectrum for each tube.
21. Save your spectra, send them to your lab partner(s), and compare your spectra with your classmates. 6. Prepare a lab report. Include the five spectra you made in class and the answers to the questions below.
22. a) You may hand write and scan it or you may use a word processor (e.g. Office or Powerpoint).
23. b) Your report must be in a single PDF format document.
24. c) You should do this lab with a partner and talk with them about the write up but this write up must be your own work in your own words.
25. d) You can (and should) compare your spectra to the images that other people took but for your report you must use the images you and your lab partner took not images taken by someone else.
26. e) You must each submit your own report.
27. f) The lab report should use complete sentences to describe what you did, and what you saw.
28. g) Your instructor will give you additional instructions for the correct format and form of your report.
29. h) When you have completed your lab report upload it to Blackboard using the link in the Lab 4 folder.
30. Do the post lab quiz on Blackboard. You may, but don’t have to, work with your lab partner on the quiz.

Questions

1. Which spectrum from a labeled tubed matched the unlabeled tube? What was the gas in the unlabeled tube?
2. Some of the labeled tubes contained atomic gas (e.g. hydrogen and helium) and some contained molecular gas. How were the spectra different?
3. By eye, were the colors of the bulbs different? Can you tell the type of gas by just looking at the tube? Is that true for all of the tubes?
4. Describe the lines you saw in the hydrogen spectrum. Describe the color.
5. What are the lines in the hydrogen spectrum you recorded called? How many lines do you see in your hydrogen spectrum? How many are there? Can you see them all? If not, why not?