GENERAL INFORMATION AND LABORATORY MANUAL

 

Physics Laboratory PHYS 506   and Advanced Physics Laboratory PHYS 616

(8/17/01)

 

 

Table of contents

 

 

 

General Information

 

This laboratory will acquaint you with “classic” experiments related to the quantum structure of matter and with modern experiments similar to those which you might encounter in research laboratories today. You will learn techniques of data taking and analysis. You will learn how to keep a data book. You will gain some familiarity with modern research apparatus and with concepts used in current physics research. You will learn how to search out literature on a project and to think your way through an experiment without being led by the hand through each step. You will learn how to write a comprehensible report on your experiment, following roughly the same format you would use in writing a research publication in physics. You will also learn to present a comprehensible oral description of your work.

 

Texts

Required: Data and error analysis , William Lichten, Prentice-Hall, 1999

                        This is a useful description and reference manual of error analysis.

Recommended: Experiments in Modern Physics, A.Melissinos, AP, 1966.

This is a quite old, but still very useful, description of many of the experiments carried out in this laboratory. The techniques are our of date, but the physics is not. Two copies of this book are on reserve in the physics library and one copy is kept in the laboratory.

 

Writeups and further literature on specific experiments are provided in this manual , in class and are often on the web.

 

General procedures

 

Recitation: (M 3:30-4:20) During approximately the first month  this will be used for a discussion of error analysis and possibly discussion of experiments that concern everyone. During the remainder of the course this time will be used for oral interviews.

 

Laboratory time:  (T,U 1:30-4:20) Attendance during this time is not optional. You should come on time and stay for the whole period. During this time you will perform, with one or two laboratory partners, about seven experiments over the course of the semester. These are to be chosen from the list below. Try to start with one of the “classic” experiments from group 1. Each experiment will take you typically one to two weeks to complete. It is more important to do the experiment right than it is to stay on some preset schedule. You should read the writeup and enough additional literature BEFORE STARTING THE EXPERIMENT so that you understand what the main idea is. Your instructor may ask you a few questions to be sure that you have done this before you start. You will record your laboratory work and data in your data book . After you complete the experiment you will analyze the results and write a formal report, largely outside of class. The final report will be due on Thursday of the week following that in which you complete the experiment. You will not be allowed to start a new experiment if you have more than one completed experiment for which you have not turned in a report. Do not procrastinate. After you hand in the report, you, with your laboratory partner, will give have an oral interview with the instructor on each experiment. This interview will give you, and the instructor, a chance to explore to what extent you really understood what you were doing and to clear up any residual questions. The interviews will be scheduled for Monday afternoon and should take place the week following the Thursday on which you turned in the report.  There will be  signup sheets for scheduling the experiments and the oral reports.

 

 

 

Experiments

 

Name                                                               Estimated number wks

 

1. “Classic”                                                                                        

1.Millikan Oil Drop                                                    2

2. e/m Bainbridge                                                        1         

3. e/m Hoag                                                                 1

4. Speed of light                                                          1

2. Atomic structure/quantum mechanics/modern physics

5. Rutherford scattering                                               2

            6.Franck-Hertz                                                            1

            7.Interferometer                                                           1+

            8.Microwave Optics                                                   1+

            9.Electron Diffraction                                                 1+

            10.X-ray Diffraction                                                   2

            11.Nuclear magnetic resonance                                   2

/ electron spin resonance

12.Photon and particle detectors                                 2

            13.Zeeman effect                                                         2

            14.Moessbauer effect                                                  2

            15.Atomic spectra of the elements                              2-

            16.Lifetime of the m meson                                          2

            17.SQUID                                                                   2

            18.Scanning tunneling microscope                              2

           

 

 

Data book

 

    You should purchase a quadrille-lined bound data book (not loose-leaf or spiral notebook) for the laboratory. If the pages are not numbered, number them as you go and leave room at the beginning for a table of contents. In this book  you will keep a running description of what you did during the laboratory period. A good format is to write a very brief description of what the goal of the experiment is and roughly how you are going about it (details not necessary) and follow this by a running “diary” of what you did and why you did it. Data should be entered in a neat and comprehensible way, usually in tabular form, with units. It is OK for one student to make the original data table as you go, but the others in the group should fill in their own tables in their own books immediately afterwards. Each student must keep a data book.

    The major failing of students when they first try to keep data books is that they do not write enough English prose for the reader to know what they are doing . You should try to write the book so that another student can read and understand it. If another student cannot read it, you will not be able to read it  either a month (or less!) after you write it. Part of your grade in the course will be based on the comprehensibility and neatness of your data book. Try not to fill the book with scratch work. Either scratch on scratch paper or dedicate a separate section of the book to scratch. NEVER RECORD ORIGINAL DATA ON SCRATCH PAPER, with the plan to transcribe it later. Get in the habit of thinking out what you are going to measure before you start measuring, so that you can enter the data as you take it in a neat and legible way. NEVER LEAVE LOOSE PAPERS IN YOUR DATA BOOK.  You will often find it helpful to make sketches or to do rough calculations before you start. This belongs in the data book. You will often find it helpful to make quick graphs of some quantity as you go. This belongs in the data book. You might find it useful to do some calculation with, for example, Excel (or some other spread sheet) and maybe graph the results. Print it out and paste it into the data book. Try to keep the data book in a logical temporal sequence so that one page leads logically to the next.  

 

 

 

 

Experimental procedure

 

Prepare:  Read the laboratory writeup and enough backgound material to have an understanding of what the main idea of the experiment is. The background material includes xerox copies of printed material on the experiment and descriptions in Melissinos or other references cited in the writeups. You do not have to understand everything there is to know about the experiment , especially all the details of operation of the equipment, but you must understand the main idea. What are you trying to determine, what are you going to measure, how are you going to go about it?

 

Approach the equipment:  Be sure you understand the operation of each component of the equipment. IF IN DOUBT, ASK! If you just play around randomly with equipment which you do not understand, you may injure yourself and the equipment. Please do not do this!  BE PARTICULARLY CAREFUL ABOUT SAFETY ISSUES. Possible dangerous aspects of the labs. include electrical shock, radiation exposure, laser damage to eyes,  dropping lead bricks on your toes, etc. There are some safety guidelines later in this writeup. You should read the relevant sections before you start any particular experiment. Pay special attention to the warnings given in the writeups. Some of the apparatus is expensive and can be damaged if you do the wrong thing. The writeups are often not cook-book, so you will have to think about what you are doing.

 

Carry out the experiment: Think about the data as it comes in. Does it make sense? Often it is useful to do sample calculations after a few data points to see if things seem to be working. Record data, procedures, etc. in your data book. Record anything you will need to evaluate (estimate) the error bars on your data.

 

Reports

 

 Each student must write a report on each experiment. You are welcome to collaborate with anyone, especially your laboratory partners, on all other aspects of the experiment, BUT YOU MUST WRITE YOUR OWN REPORT IN YOUR OWN WORDS. There is no set format, but try to imagine that you are writing for publication in a professional physics journal. Several examples of research publications from The Physical Review will be provided in the laboratory. You will notice that a typical format includes the following sections:

1) Abstract: A short paragraph, probably only three to four sentences, describing what you measured, the general method you used, what result you obtained and perhaps what you concluded from this result. This is for the reader who wants to know at a glance what the content of the article is and whether it is interesting to read it in detail.

2) Introduction: Give any background necessary to place the experiment in context. This can be an historical context “When Rutherford did his classic experiments on the scattering of alpha particles from gold, it was not known how the positive and negative charges were distributed in the atom. ....” or perhaps a more current scientific one “ It has recently been shown that materials cooled below a certain temperature lose their resistivity altogether. .....”.  Then explain what the purpose of the present experiment is, what you want to find and how you are going to do it. Give enough background so that another student could understand the general what, why and how of the experiment.

3) Experiment: Explain how the experimental setup functions. Diagrams are useful. Explain how you took the data. You do not have to include raw data usually , but you can include any graphs or tables which are useful to explaining what you found.

4) Results and analysis: Show the results with error bars. This is often presented in the form of graphs or tables. Discuss any analysis you did to go from the raw data to the results. Discuss how you calculated or estimated the error bars. NEVER “FUDGE’ THE DATA. If the experiment gave an erroneous result, and you know it, try to explain why. The purpose of the experiment is to pose questions of mother nature and to explain the answer you got, not to “get the right answer”.

5) Discussion and conclusions:  What do you conclude from the data? Did it agree with your expectations or with previous values? Why or why not? This is the section in which to answer questions posed in the writeups and to discuss any aspect of the experiment which you feel needs discussing. Feel free to theorize on what worked well or went wrong, how the experiment could be improved (do not waste time just saying “the apparatus needed to be more accurate”). Be creative.

 

    Your reports should be written in a professional manner with MS Word, Wordperfect, LATEX or some equivalent program. The graphs should be printed , and possibly inserted into the text, using a program such as Excel or equivalent. There will be several PC s available to you in the laboratory for both data reduction and report writing. MS office programs including MS Word and Excel will be available.  To log on to these computers  the user name and password are both Phys506. A sub directory on the physics department server has been created for you. In this directory, you will find one general class directory which your instructor can use to keep information of general use for the whole class. You can read from this directory, but not write into it. You are welcome to create a subdirectory with your last name and to use it to store data, reports, anything you want. However, you should probably back everything up on a floppy disk which you keep with you always in the laboratory and which you take home with you at the end of the day. Please do not play with anybody else’s directory. We work on the honor system here.

 

    Plagiarism questions: It is very tempting to cut and paste from other sources into a report. DO NOT DO THIS. If you quote from (or cut and paste from ) another document, you must place it in quotes and cite the reference. If you use a figure from another document (this is sometime acceptable), you must credit the source.  Do not cut and paste text from the laboratory writeups into report.  Plagiarism is a violation of the University Honor Code. It also cheats you out of your university education.

 

Oral interview

 

   Starting approximately three weeks into the course, you will have an oral interview with your instructor at the end of each experiment. This will take place in the instructors office and will be scheduled on a signup sheet on the laboratory door. The interview should be done as much as possible on the Monday following the Thursday you handed in your report. You and your laboratory partners will appear as a group. The interview will last about twenty minutes. You will be expected to understand the physics of the experiment and how the experiment itself worked. This is an opportunity for the instructor to find out whether you really understand what you are doing and for you to clear up any remaining misconceptions or problems.