In order to help students understand what is required for a proper formal lab report in this course we outline the basics required for each section then provide a will walk-through the example of a speed of light experiment. This example lab report covers the entire experiment.
Here are some basic rules for a formal lab report:
We begin by explaining what is required in each section of a formal lab report ...
The ABSTRACT contains One or Two paragraphs at most outlining what you did (the basic steps you went through to complete the experiment) and a quick summary of KEY results. Begin by stating why this was experiment done ("In this experiment the effect of pressure on a gaseous discharge in air is examined ..."). Next, state how it was done ("Using a vacuum system consisting of a turbomolecular pump ...") Finally state basic observations including any important numbers here such as key pressures ("at xxx.x torr the discharge was observed to be in the form of discs...") and measured spectral lines (just key ones since a table of twenty numbers is unsuitable for an abstract, something like "In the neon discharge a line at xxx.x nm was observed. This is not a neon line but rather was found to originate from nitrogen contamination in the tube ..."). Verbose abstracts with _too_ much information will be penalized marks.
The BACKGROUND consists of several pages summarizing specific theory and principles used in the lab - while some theory may be obvious (like the relationship between the velocity of an object and the distance travelled), some concepts are obscure and need to be explained here so the reader of the lab has an idea of what was done. Include (1) basic configuration of equipment used, (2) the operating principles of anything unusual or special (e.g. a turbomolecular pump), and (3) explain any concepts required to understand the lab. Include expressions required for the prelab (If a concept was in the prelab, it was probably required to fully understand the experiment).
Diagrams of system components are required (e.g. a diagram of how a turbomolecular pump operates would be wise since a picture is worth 1000 words and no one wants to read a 1000 word description on how this pump works). Remember, though, that a picture without an explanation (in WORDS) 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 single concept as applied in a lab (although there may be several concepts worth discussing).
Once again: AVOID a description copied directly from a resource like the web or a book: describe it YOURSELF in YOUR OWN WORDS.
PROCEDURES explain what you actually did and the steps needed to perform the task. This should include enough detail to allow another person to duplicate the lab and obtain your results. Here you would NEVER include a cut-and-paste of this outline (unless your lab mark is too high and needs reduction) but would rather include a PROPERLY EDITED description of what you actually did. Avoid irrelevant details such as "I walked into the lab and took off my coat ...", "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" (I'm not kidding, I got that one once on a lab).
Literary diarrhea such as "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 ..." 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 is irrelevant, I'm sure a green know would work just as well :). As well, specific details of 'what valve was turned when' are NOT required but rather a simple description such as "The manifold and tube were pumped to an ultimate pressure of xxx.xx torr then the manifold was sealed from the pump using the evacuate valve" or "a mercury spectrum tube was inserted into the power supply and a reference trace taken". It is likely that anyone in the world trying to reproduce this experiment would have similar, but not identical, equipment so details _too_ specific to this particular system are unnecessary. Another trap NOT to fall into is copying instructions from a text verbatim where they do NOT apply to this specific system (e.g. overzealous cut-and-paste).
Include relevant figures and numbers into the procedures (e.g. "The tube was pumped to 1.3*10-5 torr …", "A US-Lasers 808-5 diode laser operating at a measured wavelength of 806.6nm at a power output of 3.4mW was employed", or "20mA of drive current was used to excite the discharge"). Describe the figures you ACTUALLY used in the lab (as opposed to cutting-and-pasting the incorrect ones from a lab outline). Two or three pages should suffice since you would not mention every single step.
OBSERVATIONS detail what happened during the experiment and the results. Include drawings of observations if required to describe what you saw (and don't forget a figure # and WORDS to describe the drawings - drawings of discs in a glass tube without words to go with it are a bit like inkblots and open to interpretation ... avoid this). Tables of observed data (e.g. emission lines) are great however be sure to describe how they were observed/calculated (especially if the table has columns which represent the result of a particular computation such as error from a unknown). An example calculation showing the methodology for calculation is a must! If you were required to compute ten values, outline the computations for the FIRST one in the table then present all ten in a table form (since the other nine involve the exact same calculations)..
The CONCLUSIONS are usually a page or two summary explaining the observed results. Here you'd include a summary of observed results and quite possibly repeat (but in a very condensed and summarized form) some observations in order to illustate some effects (for example, you might include one drawing of observed 'discs' in a gas discharge to illustrate such an effect). Do NOT include a chart of observed spectral lines here but instead discuss where they came from (you might mention a few specific lines, but don't include an entire table again). In the case of a spectroscopy experiment with, say, neon gas you'd identify lines _NOT_ from neon here (anything blue and violet is definately not from neon) listing their wavelength and postulate where they came from.
REFERENCES should not be on a separate page but rather as a footnote on each page. If you used a diagram from a reference in the background section quote the source as a footnote on that page. Similarly if you quoted that the red line of krypton gas has a known wavelength of 647.1nm, use a footnote to show the source of this figure (e.g. "Source - NIST eBook"). Marks will be deducted for numbers and figures without proper references. Do you need a reference? ... if a physical constant is commonly known, no, but if it is a magic number like an wavelength of an emission line from oxygen found as a residual is a "pure" neon discharge, then yes.
... and keep lab reports in third-person, in terms of "... was done" or "the chamber was pumped" as opposed to "We pumped the chamber" or "My buddy sat on his butt watching us" ... keep personal opinions and descriptions out of lab reports.
Now, let's use the specific example of a complete lab report for a "speed of light" experiment to illustrate each section.
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.
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).
A complete description (in both words and diagrams) of the experiment performed including details of equipment setup. Consider the following narrative:
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:
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).
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 always included in a lab handout to help you USE the equipment but aren't relevant in a lab write-up (e.g. a lab outline might say "wait until the LOS/Loss-Of-Signal lamp is extinguished before proceeding" but this may not be relevant as it is very specific to the equipment employed). CUT-AND-PASTE VERBAL DIARRHEA (just because you were too lazy to edit some lousy text) will lead to a HUGE 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 knob 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 - we are NOT shopping for window treatments!
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:
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:
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.
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.
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.
An informal lab report varies in format: sometimes you are asked to outline the experiment in a paragraph or two then jump right into the observations, sometimes it is simply a collection of questions (Q1, Q2, etc) to be answered. Where a lab report asks you to answer questions, consider the following helpful hints:
Base answers on scientific fact, not colloquialisms. If one were to ask "Why is a dielectric filter better than a gel filter?" one could say "It isolates one colour better than others" but that is vague, and certainly not worth much as an explanation in terms of explaining why it is better (it is also not worth much in terms of marks!). Among other things, we never speak of 'colour' - in scientific terms always refer to wavelength. 'Colour' is a subjective thing, wavelength is something one cannot argue about (e.g. is the 488nm line of the argon laser blue or cyan? Regardless, one cannot argue about wavelength.
A better answer would be "dielectric filters offer a much more narrow spectral passband than gel filters which frequently allow wavelengths spanning hundreds of nanometers (FWHM) to pass. In contrast, even an inexpensive dielectric filter might feature a passband of less than 20nm." This is scientiic, and based on fact (or observations).
When a question is asked such as "why is a p-i-n diode best suited for this purpose" one is expected to research a p-i-n diode ("Googling" a manufacturer's website and examining datasheets is a good idea) to determine the characteristics for which it excels. One might mention that such detectors are fast (quoting speeds like "frequently, risetimes of such diodes are less than 20ns"). One could even contrast other detectors to point-out why these detectors are slower (or at least quote speeds of other types for comparison).
Many answers to questions from a particular lab might well be found in the SOPs and related manuals for equipment in the lab. A favourite place to find answers is the assigned PRELAB readings.
When a questions looks simple, such as "What is a monochromator ?", it probably requires more explanation than "a box that separates colours"! The correct proedure to answer this question would be to describe what the thing does and how it does it. Again, "googling" a commercial manufacturer of such equipment will likely provide a wealth of information including optical arrangement (Ever hear of "Czerny-Turner"?? You should). If a lab has only seven questions, but counts as a full lab, one expects each question to have a decent and complete answer, not superficial.
And once again, AVOID cut-and-paste jobs from some wiki page you read - PUT IT IN YOUR OWN WORDS. As a professor, the hope is that you'll read how the device works, actually make a point of UNDERSTANDING the operating principles, and by writing it down demonstrate your knowledge of this. And a "captain obvious" hint here: you very well might be given a second chance to demonstrate your knowledge of operating principles on be NEXT MIDTERM so be sure you actually "get it" and aren't just "going through the motions".
Where a question says "Compare ..." the correct answer will likely present data from an experiment in the form of a table as well as a discussion (in WORDS) interpreting the data. If one was comparing, for example, the intensities of transitions between the 3p-3s and 5s-3p quantum systems, you'd start with a table of data then a paragraph describing the interpretation. The table of data might include the wavelength, precise levels involved (to attribute them properly to a quantum system), and both observed (raw) and normalized intensities. Where a normalization is undertaken, one must describe how it was done and the unity reference employed. As for discussion, comments like "In all cases, transitions in the 3p-3s system revealed higher overall intensities than those in the 5s-3p system however the presence of helium in the discharge was found to increase the intensity ...[yadda yadda] ... by and average 50%. The logical interpretation of these results suggests that helium provides a direct pathway to ... [yadda yadda] ... as described in Csele, in section 4.3"). One might even include a diagram from a reference (4.3.3 ?) showing how a particular effect works.