Appendix 2

 

I.  Lab Guide  (In Brief)

Time For a Discussion About Labs

 

INTRODUCTION

 

 

The purpose of the lab exercises is 4-fold:

 

                        1.  To contribute to your understanding of concepts discussed in the lectures.

                        2.  Give you practice using the scientific method.  (That is, i. Examining a phenomenon, ii.  making a "guess" or hypothesis about that phenomenon, iii.  testing your hypothesis.).

                        3.  Give you practice writing technical reports.  In other words, translating what you've done into plain english.

                        4.  Give you practice using scientific equipment and adjusting it for optimum accuracy.

 

Error and uncertainty in a measurement.

 

            ERROR is the difference between your answer and the "real" answer.  Error can only be calculated when the "real" answer in known.  In some experiments this will be the case and you will be asked to calculate your

 

                         percent error = | your answer - "real" answer | x100

                                                            "real" answer

 

            In other cases there will be no "real" answer.  So you will be asked to cross-check yourself by finding the measurement two different ways and comparing the results by finding the percent difference between them.

                              

                        percent difference = | Ans1 - Ans2 | x 200

                                                               Ans1 + Ans2

UNCERTAINTY in a measurement is a quantification of the limitation of the measuring instruments.  It is the maximum difference between your measurement of some quantity and it's actual value, which is unknown.  If the result under examination requires only the measurement of a single quantity, then the uncertainty in your result depends only on the smallest increment of the measuring device and the number of measurements you make of the quantity in question.

 

In particular, we will use the following rules for this course:

 

If you make:

           

                        1 measurement, uncertainty (unc)= ± .5 of the smallest increment of the measuring device.

 

                                    2 - 5 measurements, unc = ±1/5 the smallest increment of the measuring device.

 

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II.  A Guide to Writing a Lab Report (Detailed)

 

            THE LABORATORY REPORT

 

            You are required to submit a neat, well-organized, well-written report for each experiment.  The report should be prepared in ink or typed and should be written on one side of a sheet of paper.  The length of a report will vary widely from person to person and experiment to experiment.  However, reports should not exceed 18 to 20 pages.  Nearly all of the experiments in our courses attempt to convey very simple concepts, hence lengthy reports only show that something is wrong with either the procedure, the experiment, or heaven forbid, your work.

 

I  The Components Of A Good Laboratory Report

 

The physics laboratory report consists of the following sections:

 

l)  Title page

2)  Introduction

3)  Data Table(s)

4)  Data analysis:  sample calculations, graphs, table(s) or result(s)

5)  Discussion of analysis

6)  Conclusions

7)  Questions

 

A)  The title page must include:

    a)  The identifying number and title of the experiment

    b)  The date the experiment was performed

    c)  The date the report was submitted

    d)  The name of the author and author's lab partner

    e)  The course number

 

B)  The Introduction

 

            Tell what you are going to do.  (i.e. State the experimental objective).

            Tell how you are going to do it.  (A brief description of the procedure.)

            Tell why you are doing it.  (What you want to find or prove.)

 

            Also, deviations from the manual's procedure should be discussed in the introduction.  Do NOT include any exposition on the theory behind the experiment or intricate details of the procedures you followed.  This information is in the laboratory manuals and there is no sense in repeating it in your report.  Remember you are reporting on the RESULTS of your experiment therefore keep your introduction brief.

 

C)  The Data Table(s)

 

            Data should be recorded on a pre-designed data sheet (from when you read the lab before coming to do it), this can be drawn up by hand or made up on the computer.  The data must be well organized, well labeled and easy to understand.  If your original data sheet is not presentable, you may rewrite this data sheet.  However one of the goals of this course is to teach you the correct way to record data as the numbers are first taken.  Hence you should work toward the goal of NOT having to rewrite your data sheets.

            The original data sheet(s) must be included in your lab report, even if you reorganize the data later on a spread sheet.  Formulas must be given for any quantities , (in a table, for instance) that are calculated from data rather than recorded as data . 

 

D)  Data Analysis

 

1)  Sample Calculations

 

            Quite often it will be necessary to perform the same basic calculation several times on different sets of data.  In these cases only ONE complete sample calculation need be included in your report.  The results of all other similar calculations could then be summarized in a table of results.  When the experiment consists of just one basic calculation carried out on one set of data, work out the computation in full detail.   Remember to do the following with all calculations you perform in your report:

 

            a)  Present the calculation neatly and in complete detail.

            b)  Include all the necessary units and show how they cancel to give the proper units of the result.

            c)  Carry all phases of calculations to as many significant figures as the data warrants.

            d)  When required, display calculations of propagated uncertainties separately from calculations of the quantities themselves.

2)  Graphs

 

            Place graphs immediately following all calculations or where they logically fit into the entire data analysis section.  Remember, these graphs should be self-explanatory and must include a title, circled data points, properly labeled axes and units.

 

3)  Table(s) of Result(s)

 

            Rewrite results separately (usually in a table) from all sample calculations.  Column headings in the table should be large enough so that you can state the equation you used to compute all the numbers that fall under that column heading when necessary.  (Any numbers not recorded as data must have a formula to justify from whence they have come.

 

E) Discussion of Analysis (DOA) (Find excuses for your error.)

 

            Briefly, the DOA is a discussion of your error; what caused it, and what you could do to prevent it.  This is the most important part of your report.  Your discussion should show that you have thought critically about the experiment.

 

            In most experiments this means examining the consistency of your data, and comparing your results to those expected.  In a couple, however, we'll "do it up proper", which means comparing the difference between experimental and theoretical outcomes (d) and the calculated standard deviation of this difference (sd).  Namely, whether or not d < sd.

 

            Various sources of error can be cited in the discussion, however nothing is to be gained by merely writing a litany of "possible" errors.  You must think critically about how these errors might have affected your results.  For example, would the error you cite tend to increase or decrease your numerical result?  Which one of  the quantities measured has the largest uncertainty and could this account for most (or all) of your error?  Lastly, if you do list several sources of error, rank them in order of importance. 

 

            If your results lead you to conclude that the theory is faulty, you should present the basis for your opinion.  You may wish to discuss possible additional experiments to test your opinion or alternate ways to perform the experiment.

 

F)  The Conclusion

 

            The conclusion is a one or two sentence summary of the entire experiment.  Ideally, anyone should be able to read your introduction to learn what you set out to accomplish and then read your conclusion to learn whether or not you reached this goal.  In other words, tell what happened, (what results were and what error or uncertainties were if appropriate), and how you feel about the outcome.

 

            Always restate your results (with their accompanying uncertainties) in the conclusion.  Make sure that all the questions asked in the experiment write up have been answered.  If these questions were answered in the Data Analysis section, restate those answers in the conclusion.  Lastly, comment on the success or failure of the experiment as a whole.

 

II  Laboratory Report Checklist

 

l)  Title page:

 

            a)  Have you identified your experiment, lab partner, section, date of experiment and date of submission of final report?

 

2)  Introduction:

 

            a)  Have you stated the purpose of the experiment?

            b)  Have you, very briefly, told what you are doing and how it relates to the theory?

 

3)  Data:

 

            a)  Are original data sheets (signed by the instructor) included?

            b)  Is data clearly displayed in the report, with references to any adjustment of equipment?

            c)  Are units properly included?

d)  Is random error evaluated, including standard deviations of the mean wherever a statistical treatment is appropriate?

e)  Are estimated uncertainties and specified accuracies for instruments such as electrical meters recorded?

 

4)  Data Analysis:

 

Calculations:   a)  Can the reader follow how they were made from your data?

                        b)  Are rules concerning significant figures observed?

                        c)  Are deviations of means and estimated uncertainties in results expressed as standard deviations percent uncertainties of results?

 

Graphs:                       a)  Are graphs neat and properly labelled with proper units and captions?

                                    b)  Are graph scales well chosen for the data?

                                    c)  Are data points properly circled, with error bars where appropriate?

 

Results:           a)  Are final results clearly identified with units and uncertainties?

                        b)  Are groups of results tabulated for easy comparison?

 

5)  Discussion of Analysis:

 

a)  Have you indicated the actual disagreements between your results and the theoretical predication, and have you compared them with the propagated uncertainty you could expect in view of the uncertainties in the measurements?  (Required only if specifically stated).

 

b)  Have you identified likely systematic errors and shown how their magnitudes could be responsible for any actual disagreements greater than those expected from uncertainties in measurements?

 

            c)  Are there peculiarities in data or results that should be pointed out and explained?

 

            d)  How and to what extent are the physical principles confirmed by the experiment?

            e)  How could the experiment be significantly improved?

 

6)  Conclusion:  

 

            a)  Have you stated results and given errors or uncertainties ?

            b)  Have you, very briefly, summarized the amount of success you had in the experiment ?

 

7)  Questions:   a)  Are all questions in the laboratory manual answered?

 

All lab reports should be typed, except for data sheets, graphs and calculations, (you gotta join the real world sooner or later), but handwritten reports will be accepted.

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