Physics 225b Lab Information and Help page.

groups for this semester

Group 1(4-7pm) Ryan and Robert and Roberto

Group 2(4-7pm) Cliff and Ben

Group 3(4-7pm) Chris and Colin

Group 4(4-7pm) Amanda, Ellis

Group 1(7-10pm) Katie, Patrick, and Anthony

Group 2(7-10pm) Michael and Eric

Group 3(7-10pm) John B. and John P.

Plan for the semester

For each lab below, I have written down what I think are the important hypotheses to address in your lab report. The laboratory writeups and procedures supplied on the web page are there to let you become familiar with the experimental techniques and the questions asked in the writeups are meant to stimulate your thinking. The questions from the write-ups are useful, and I expect you to answer them. I've added some notes on each experiment to guide your (short! 1-3 pages!) lab report. Be sure your arguments are consistent with your data and analysis.

Instructor: Will Johns < will.johns@vanderbilt.edu>

Office: SC6906 and SC6924

Phone: 34(3-8295)

Office Hours: Thursday Afternoon before colloquium (You can try other times too, I may be busy.)

TA: ?

You are required use the electronic logbook that you used last semester. Please include in your logbook your notes and your primary data and observations. The bulk of your work, including the answers to the questions asked from the writeup, should be in your lab book. Your lab book should be kept in a way that lets your work be repeated by other people. (Especially me!) If I can't repeat your analysis from the supplied information, I can't grade your report.

In your lab report, please summarize your findings, including any error estimates you make. Attach it to your notes etc. in the Electronic lab book

The lab report for a particular lab is nominally due one week after you finish the analysis in the class period following the data taking (if any), or one week the data taking (for the Transistor or Op Amp labs). In principle, the summary should not take a great deal of outside lab time. If you are doing things right, you will spend more time preparing for the lab than writing the summary.

If possible, you should take some time and ask someone who is doing the lab you are going to work on next 1) what to watch out for, 2) what they are doing, and 3) can I see how that works? An investment of a few minutes here can save you an hour or more when you do the lab.

The lab has traditionally been worth 25% of your 225b grade. Each Lab report gets a score of 100 points. 50 of those points are for your results being consistent with your data, and for your data being consistent with what you were supposed to be doing. (I.e. you can't measure the outside temperature instead of the muon lifetime and say what the outside temperature was in your report and expect 50 points! Likewise, if you made your best effort to take the data and it's just plain wrong, and you report this well, this is an honest report and I can't see knocking off points because of that.) So I really need your summary in addition to the copy of the lab book pages. The remaining 50 points are for how you handled the questions asked in the lab write up and how well you addressed the hypothesis and summarized you results in the lab report.

We will have 14 lab periods together, though the first three periods consist of an introduction and safety orientation, a group lab, and a group analysis project. The Transistor, Op Amp, Polarization and Muon labs are 2 week labs, but the others have been done in a single week. Additionally, there is an extra lab period for each experiment (except Transistor, Op Amp, Gamma Spectroscopy and Prop tube) devoted to doing your analysis. So, for instance, the data taking for the polarization lab is completed in 2 weeks, and then the next week we work on the data analysis during the lab period. Since people usually burn out on doing both the Transistor and the Op Amp lab, I'll ask you to do just one of them.

Overall, I'm easy to keep happy. Keep a good logbook with all your data and notes in it. Keep your summary (lab report) useful and correct (and brief if possible). I have been known to mark reports up and have you rewrite them.

I will be adding extra stuff to these labs since we are expanding the analysis aspect of the lab course this year.

Transistor Lab: The electrical behavior of a 2N3904 transistor is described by simple rules.
- This lab is set up to try and address this hypothesis already through a series of circuit challenges. Keep in mind that getting the circuits to work is what you will spend most of your time on.
- In your write up describe your findings for each part.
Op Amp Lab: The electrical behavior of a 741 Op Amp is described by simple rules.
- This lab is set up to try and address this hypothesis already through a series of circuit challenges. Keep in mind that getting the circuits to work is what you will spend most of your time on.
- In your write up describe your findings for each part.
Muon Lab: The muon has a lifetime of 2.1970 microseconds. (Part 1) (Part 2) (Express Setup) (Setup Principle) (Setup data taking suggestions) (A note on "deadtime".)
- This lab is set up to try and address this hypothesis through measuring the muon lifetime with a block of scintillator.
- In your write up describe your findings for each part. You will have to verify that the setup is working before you begin the experiment, and you will perform an analysis of the data once it is collected. I am currently working on making the setup a separate lab. You may be a Guinnea Pig!
Gamma Coincidence:(new write-up!) The photons emitted from a low energy positron anhiliation with an electron are emitted at an angle of 180 degrees with respect to each other. You can find an example of finding averages and so on from histogrammed data here
- This is a very interesting lab from the viewpoint of errors and experimental precision. There are a lot of variables to consider. Some of the more important ones are source placement and detector placement. Incorporating these uncertainties in your report will be most of your work. A calculation of the effects is much easier than determining them experimentally! If you want more info on the equipment, you can find it here. (Big file!)
Polarization: Visible light is an electromagnetic wave and its properties can be changed with a magnetic field. The intensity of light transmitted through a polarizer obeys a cosine squared law.
- This lab has traditionally been run by Dr. Webster. I find it interesting that a magnetic field has a measurable effect on the polarization of light. The instrument you will be using has a lot of precision, so try to be quantitative. Here is an example of a fit to a straight line for just 4 points that you may find useful. Also, here is a note on determining errors from your various angle measurements.
Gamma Spectroscopy: (One week total) 1) The horns below the main gamma peak are the limits of the Compton energies. 2) The ore sample is composed primarily of Uranium 238.
- This lab is is a high resolution measurement of deposited energy due to nuclear transitions and decays. A lot of the lab is spent calibrating the instrument, and you will test your calibration with an unknown source. Then you will look at a sample of Uranite ore to try and identify the parent of the decay products. (You used this ore sample last semester for the geiger lab.)
- In your write up describe quantitatively the deposited energy spectra you see for Na-22, and justify your findings for the ore sample.
Proportional Tube: (One week total) The gain in a proportional tube is an exponential function of the voltage and the physical characteristics of the tube and the gas employed.
- Believe it or not, this is a good way to measure the energy of x-ray like photons. There's a lot of math in this one, so careful preparation is important. (Pictures of the procedure)
Sample Lab, Lab Book pages and report

Gamma Ray Absorption: Absorption of gamma rays by material is an exponential process.

Lab Book pages: I got a little carried away with fitting stuff.

Lab Report: A brief note on what we did, what happened and what to do next.

Lab Report: A brief note on what we did in 2007.

Excel Example in .xls file of the 2006 Collimated data: You can modify this file and fit data that you have to a straight line. Be sure that you do modify and pay attantion to what you are doing. Here is the Un-Collimated excel file.

2008 Data and notes Data and notes on what we did in 2008.

2008 Data and notes Rough graph with what we did in 2008.

Source material, downloads etc.

Intro to Statistics

Notes: Some of this I skipped in class cause you guys said you were familiar with a gaussian and counting statistics.

Poisson Distribution

Poisson and Gaussian Distributions

Sum of Random Numbers

Gaussian Behavior of random sum

Intro to fitting and parameter determination

Notes : This has the correlated errors and the gory math details of the fit to a straight line taking errors on y into account.

Next, I rebin some exponentially distributed data, take the natural log of the bin entries and fit the data with a method described in class. On the first page, I show a fit to the exponentail using a sophisticated fitting program. The next page down has the example using the technique from the notes and from the class discussion we had on the exponential decay. This is a very useful technique!

Exponential Decay Data

Example of fitting to Exponential Decay Data
Data used in fit example.

Powerful and Free analysis and fitting package (PAW) Intro to Physics "spreadsheeting" with PAW

Other Web pages to check out: (Note: this is the official class web site.)

Vanderbilt Safety Page Lots of info on Doctors and patients. Have to dig for pertinent info.

Prof. Webster's page of 225 labs and info

My old 225 lab and info page

My old 225b course and info page (There are worked homework problems here!)

Thanks, w.j.

Physics 225b Lab Information and Help page.

Sample Lab, Lab Book pages and report

Source material, downloads etc.