Notes On Formal Lab Reports

In order to help students understand what is required for a proper lab report in this course we will walk-through the example of a speed of light experiment. This model lab report covers the entire experiment.

The Basics

Here are some basic rules for a formal lab report:

The entire report is to be WORD PROCESSED, never handwritten
Use a report cover, DO NOT simply submit staped pages - these tend to become lost in transit
Diagrams are, generally speaking, essential to explain lab setups and background information - include them
If you use a diagram, REFER to it in the text (that is the acid-test as to whether or not it is a useful diagram). A picture without an explanation is useless. Usually one decent figure paired with one decent paragraph is enough to explain a concept as applied in a lab.
Where possible, diagrams should be machine-drawn using a CAD or Paint package
Where appropriate, include scanned diagrams and figures directly into the text of the document
Each section below must begin on a separate page
Simple copying of a procedure from a lab handout is NOT sufficient - EDIT it to reflect what was actually done in the lab
Write labs in third-party: never include phrases like "I watched the gauge until it decreased to 0.0001" instead simply state "The system was pumped down to 0.0001 torr" (no one really cares if _you_ watched the gauge or a well-trained cat, the important thing is what was accomplished)
Avoid irrelevent details such as "Our group consisted of three people, one turned the valves while the other picked his nose", or "We turned on the power switch as instructed by Mr. Csele and the power lamp came on" (I'm not kidding, I got the last one on a lab)

Cover Page

Include a separate cover page stating the student's name, ID #, lab partner, and laboratory name and number:

Abstract

A single paragraph on it's OWN PAGE (the first page behind the cover) describing the experiment, basic setup, and results. Do not include details of the experiment which might make this verbose: just the basics required to let the reader know what the report is about. Consider the example from this lab:

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This abstract states:

What was done (measurement of the speed of light)
How it was done (Michelson-Foucault method)
Summary of results (two figures summarizing many experimental runs)

As a second example, consider these phrases from the abstract of a PHTN1432 lab:

The last one is a summary of a KEY observation (which alludes to a key conclusion from the lab itself). Be careful though since verbose abstracts with _too_ much information will be penalized marks.

All abstracts present a very basic description of the method used, and a summary of the results (i.e. there were four sets of results but only the final value is reported). In various scientific journals it is used when searching to determine if this report is applicable to the reader's problem.

Introduction

Sometimes called 'Background', this section describes the fundamental concepts involved. In the case of this experiment, it describes (in one paragraph) historical methods used in the 1600s and 1700s to measure the speed of light (e.g. astronomical methods). Next, the original experiment of Michelson and Foucault from the 1800s is described (again, one paragraph). This is important since it describes the method used in this particular lab. A diagram shows how the original experiment worked and several more paragraphs are required to detail the theory which governs the experiment including relevant formulae. Remember that if you include a figure, REFER to it in the text that follows ("In figure 3 a mass spectrometer is depicted showing how DC and RF voltages are superimposed ..").

The description details how the apparatus works (a basic methodology including historical references is appropriate here) and what was expected. In the example lab, four pages were required (with two embedded figures) to fully describe the concepts involved. As well, an explanation of any unusual lab equipment might well fit here - for example the operation of a vacuum pumping system and the pumps involved (an example you'll need next term in PHTN1432). For a lab using unique equipment you would describe the basic configuration of that equipment here (e.g. how an interferometer works or how a high vacuum system works), detail the operation of anything unique used in the lab (e.g. a turbomolecular pump, a lock-in amplifier, or other esoteric apparatus uncommon in the lab), and likely include a diagram or two to help explain the concept or apparatus. A diagram of the system components is often required here as is a diagram (e.g. a diagram showing how a turbo pump operates - since a picture is worth 1000 words and no one wants to read a 1000 word description on how a turbo pump works). Remember, though, that a picture without an explanation is useless. If you include a figure, REFER to it in the text that follows (that is the acid-test as to whether or not it is a useful diagram). Usually one decent figure paired with one decent paragraph is enough to explain a concept as applied in a lab.

Remember - you describe the CONCEPT of the apparatus here (or a generalized apparatus), not the actual experimental setup (save that for procedure).

Procedure

A complete description (in both words and diagrams) of the experiment performed including details of equipment setup. Consider the following narrative:

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The procedure must contain enough detail to allow a person to DUPLICATE the experiment from the description given. If the BACKGROUND section was done right, this is actually easy and surprisingly small since reference can be made to a concept explained there (i.e. two or three pages may well suffice here). If the background section described the operation of a piece of lab equipment, it is not required to repeat that information here, just refer back to it. For example, in PHTN1432 you'd describe the operation of a particular vacuum system in the background section - in this section you'd include specific details of the experiment like

Using the diffusion-pump system we rough pumped the chamber to a pressure of 8*10^-2 torr then opened the main chamber valve and used the diffusion pump to exhaust the chamber to an ultimate pressure of 3*10^-4 torr.

Note that in this example we do not mention specific operation of valves, etc since details like that would be covered in the background section.

Include a diagram showing the specific experimental setup used (this may be a generalized diagram omitting details such as optical mounts, etc. where these are irrelevant details) but be sure to include distances, focal lengths, etc. used - you'll note that key distances in this setup are included right on the figure itself instead of in a text description. In this case it was required since the diagram in the background section was too generalized and not this actual setup. An example diagram detailing the example experiment taken from the procedure is given below. Note that it is labelled figure #3: figures one and two were contained in the Background section (in this case, detailing the original experiment).

Diagram in Procedure Section

The diagram here was hand-drawn since computers were rare in the eighties ... in the 2000s we expect machine-drawn diagrams. Many times, though, diagrams can be scanned from paper and included in a lab report (i.e. from a lab handout or equipment operation manual).

Parting Shots
DO NOT COPY THE PROCEDURE FROM THE LAB HANDOUT. Lab handouts are only a general guide. The procedure must accurately reflect what was actually done as well as eliminate IRRELEVANT DETAILS which are included in a lab handout to help you USE the equipment but aren't relevant in a lab write-up. CUT-AND-PASTE VERBAL DIARRHEA (just because you were too lazy to edit some lousy text) will lead to a HUE penalty in marking!

Consider this regurgitation which serves no purpose other than to fill space: "We opened the needle valve by turning clockwise, it was a black valve with pretty blue labels, and we turned it until the gauge, which was a nice shade of red, began to increase ...". This is completely unsuitable in a professional report ... instead try "Neon was admitted into the evacuated manifold using a needle valve until the pressure in the manifold was increased to xx.x torr as read on the Baratron gauge". See the difference in professionalism as well as pertinent details!. Before including a detail, ask yourself ... does the reader NEED to know this to reproduce the experiment? (The fact that the knob was black may be relevant in the lab handout to tell you which know to turn but in a lab report it is likely irrelevant and I'm sure a green knob would work just as well :). A procedure is not the place to include esthetical descriptions.

Results/Observaions

Show all observed data. If multiple 'runs' were performed, show a graph of each (or at least a table summarizing all data). Best-fit curves or lines should be shown if the analysis requires this. As well, be sure to include estimates of ERRORS! In the case of, say, a spectroscopy lab these are easy to estimate (how small an angle can you differentiate??). Errors are best shown as +/- tolerances on each value. On a graph, show these as bars above and below observed values:

Data with Error Bars

In the case of this example lab, error bars were calculated by estimating the accuracy of measurement (in this case an error of 0.001cm was assumed: STATE ASSUMPTIONS and how you determined the error) and hence a 'low' and 'high' value for each measurement was found by adding and subtracting this amount from the observed value. The result is that each data point yields THREE numbers: the observed value, a possible 'high' value (the observed value plus the error) and a possible 'low' value (the observed value minus the error). Units may need to be converted here so be careful! Rather than show a table of results, the observations were shown in graph form for this lab as follows:

Data

Each point is shown along with error bars. There were four sets of data taken so four graphs were included here. BTW: A spreadsheet program makes childs-play of calculating errors for numerous points and allows easy graphing of the data! The graph shown was produced long before Windows even existed and so data analysis was done using a specialized scientific graphing package.

An ANALYSIS of each set of data is provided based on the slope of the resulting line on each graph and final values for each data set are reported. Show an example of calculations for ONE set of data and simple state that a similar method was used for the rest (don't be anal and save a tree at the same time). Be sure to include an analysis of results and most importantly an EXPLANATION (in words) since the presentation of numbers with no explanation is essentially useless! The analysis might be a page or two.

In previous years the biggest single problem with this section has been the LACK of an EXPLANATION. A simple table of numbers is NOT SUFFICIENT!. If, in a spectroscopy lab, you observed a line which did not belong to the species being studied you would note it here.

Conclusion

This section may also be called 'Discussion' since it presents the final results (NOT all four data runs, just the final value) - along with error results of course (the +/- tolerances). You would not include a chart of all observed data points but instead discuss where they came from (you might mention a few specific points but don't repeat an entire table of data again). You would not include a chart of ALL observed parameters here, just a simplified and condensed recap.

The source of uncertainties must be discussed here (especially if the results are lousy ... Bad results don't mean a bad mark if you can explain them!). One page is usually sufficient to summarize results and explain them.

References

OK, you have obviously stolen, errr, researched the material from somewhere - List it here. Include texts, journals, web pages, etc. Use a format as follows:

Fundamentals Of Light And Lasers, M. Csele, John Wiley & Sons, NJ, 2004

Physics: Parts I and II, D. Halliday and R. Resnick, John Wiley & Sons, NY, 1978

Introductory Applied Statistics in Science, S.C. Choi, Prentice-Hall, New Jersey, 1978

Be sure to cite sources for diagrams (lab hand-outs, etc) as well as for figures and constants quoted (i.e. if you quoted the red line of krypton as having a wavelength of 647.1nm, cite the source where you obtained this number). In general references are best cited as footnotes embedded directly within the body of the text and with the reference at the bottom of the page where it is cited.