Reports

Your experimental work in this course will be assessed both orally and in written form, both informal and formal. For the first experiment on the speed of sound, your work will be kept in your laboratory notebook, which you will submit on Thursday, September 7 at the conclusion of the laboratory period.

The pendulum experiment (which will be either your second or third experiment) will be written in a formal style centered around one or more graphs of data and its correspondence with a theory. This report will be an abbreviated technical report; it will include only the analysis portion of a normal technical report. The projectile motion experiment will be assessed in an informal oral report/conversation. Other experiments may bepresented either orally or with a formal write-up. (More on this later). This page offers guidelines for both written and oral presentation of experiments.

Oral Reports

Oral presentation of experimental may be either informal or formal. An informal presentation is a dialog about the experiment, in which the professor may frequently interrupt your presentation with questions, and in which the presentation may be guided as much by these questions as by your outline. A formal presentation is given without interruption, and is followed by a period of questions. You will present your results for the projectile motion experiment informally. The second experiment you present orally will use the formal style, which is described below.

Informal Presentation

An informal presentation is a conversation about the experiment, in which you guide the discussion, but expect frequent questions from the professor. This format allows the professor to explain points of confusion and to suggest alternative ways of thinking about the experiment, data, or results.

To prepare for an informal presentation you must finish analyzing your data, print out graphs that summarize the data and make comparisons to a theory (see Fitting Data for a discussion of this), and organize your thoughts so that you can clearly and succinctly present a summary of the most important aspects of your work. As you prepare, use the following guidelines

• Prepare one or more detailed (schematic) sketches of the experimental apparatus. On the sketches define the symbolic quantities you will use to describe and analyze the experiment. Avoid generic terms like "distance" or "time", since they could refer to many quantities associated with the experiment. When you explain the experiment(s) you performed, you should refer to the sketch(es).
• Prepare a neat summary of the theory you used to analyze your results. When you present the theory, make very clear what assumptions you are making and be prepared to justify those assumptions.
• Prepare one or more figures displaying your experimental results. Follow the guidelines described on the Fitting Data page in preparing such graphs. Be sure to use error bars to represent the uncertainties you use in fitting the data — and be sure to check the weight data box in the fit function dialog in "Kaleidagraph". Make sure that the function(s) used to fit the data are stated clearly on the graphs.
• Prepare a summary that reports the strongest quantitative conclusion(s) about your investigation that you can develop. Avoid vague (and incorrect) statements such as "Newton's laws were proven". Rather, state clearly what you have shown and how well:

  The flow of water through a 1-mm-diameter tube was found to vary with tube length L according to L^{-1.0 ± 0.1} for the range 10 cm ≤ L ≤ 50 cm. Below 10 cm the flow ...

• You are expected to know all the details of the experiment, even the portions done by your partner. "I don't know, my partner did it" is no excuse.

Formal Presentation

In a formal presentation you present an uninterrupted talk that provides the necessary background, theory, experimental details, results, analysis, and conclusions so someone unfamiliar with the experiment and your work can understand what you have done and what it means. You should assume an intelligent audience, but one that is not familiar with the details of your experiment.

Most talks use overhead transparencies or other visual aids, with which you summarize the important parts of an experiment. For Experiment 3 orals, there is no need to use transparencies, since you will be giving a one-on-one presentation. Instead, prepare your "transparencies" on paper either by hand or using a computer. They don't have to be fancy: just informative! Keep the number of words on any transparency to a minimum.

In preparing such a talk keep in mind the following points:

• For a 10-minute presentation, use the following timings as a guideline for structuring your presentation:
  • Introduction (1 minute)
  • Experimental setup (1 minute)
  • Data (1-2 minutes; could be combined with Results)
  • Results/Analysis (5 minutes)
  • Conclusions (1 minute)
• Most talks begin with a title slide which identifies the topic and the participants in the research. A well-chosen title helps orient the audience and draws them into the talk.
• Many talks follow the title slide with an outline slide. All too frequently, these look like this:
  • Introduction
  • Experimental setup
  • Data
  • Results/Analysis
  • Conclusions

  To be informative, the slide needs something more than this, since one assumes the talk will have this structure anway. In an extended talk, it can be very effective to use a few slides to introduce the topic and lay some groundwork before using an outline slide to show how the topic will be developed in the rest of the talk. In a short talk, it may be more effective to omit an outline slide and to give the lightning overview orally.

• The introduction should begin broadly, placing your experiment in as broad a context as you can in the available time. For many experiments, you can begin with some historical background on the experiment: when was it thought of and first performed and why? How did it change people's understanding of Nature, physical laws, or some small corner of science?
• As you begin discussing the particular experiment you performed it is useful to show one or more sketches of the apparatus or setup you used. Make sure appropriate quantities are labeled in type that is large enough to read easily. Label only what is necessary; simplify the diagrams as much as possible.
• Prepare one or more figures displaying your experimental results. Follow the guidelines described on the Fitting Data page in preparing such graphs. Be sure to use error bars to represent the uncertainties you use in fitting the data — and be sure to check the weight data box in the fit function dialog in "Kaleidagraph". Make sure that the function(s) used to fit the data are stated clearly on the graphs.
• Prepare a summary that reports the strongest quantitative conclusion(s) about your investigation that you can develop. Avoid vague (and incorrect) statements such as "Newton's laws were proven". Rather, state clearly what you have shown and how well:

  The flow of water through a 1-mm-diameter tube was found to vary with tube length L according to L^{-1.0 ± 0.1} for the range 10 cm ≤ L ≤ 50 cm. Below 10 cm the flow ...

  Suggest possible refinements and extensions to the experiment, or directions for future work.

Written Technical Reports

An important goal of this course is to help you learn how to express experimental observations and findings precisely and concisely. You practice this each time you write the summary section of a lab write-up. The technical report represents an extension of this activity and helps familiarize you with the format of a typical paper. Technical writing is very challenging; it takes considerable effort and practice. You will write up two experiments in a formal way. The first report will be just the analysis section of a technical report; the second report will be the full technical report. You are strongly encouraged to make appointments with the Writing Center staff to go over your drafts.

Please read the following instructions very carefully (and several times!).

Contents and Form

Your purposes are:

1. to entice the reader to continue beyond your title and abstract to read the entire paper;
2. to provide appropriate historical and technical background to motivate the experiment you conducted;
3. to explain clearly the relevant procedural issues and results;
4. to summarize key experimental findings in figures (and occasionally in tables);
5. and to provide as quantitative conclusions of your findings as you can.

The final draft should be typed (laser printed), with double-spaced lines except in the abstract. The final length should be 7—10 pages. Please see the directions for Typography for tips on getting algebraic quantities, equations, and figures to print properly. I have prepared a template that you may use to help get the layout right. It is saved in MS Word format and may be copied from the course directory on KATO.

Writing a technical report is a challenging exercise. Most of us write with difficulty and take many practice attempts to get the final product in acceptable form. Do not be alarmed. This is perfectly normal. It merely means that thinking carefully is hard.

Many journals or technical digests limit the length of abstracts. The CLEO (Conference on Lasers and Electro-Optics) digest requires 25 words or fewer. One hundred words is generous, but you must still work hard to state clearly the essential points and no more. Be as quantitative as possible.

Most people think that scientists don’t know how to write. Here’s your chance to strut your stuff! Your mission is to present a clear and convincing case for your results and conclusions.

Strategy

The sections can be written in different orders, but I recommend the following:

1. Prepare the figures
2. Write the analysis section
3. Write the conclusion
4. Write the introduction, theory, and experiment sections
5. Write the abstract

Do not begin writing the paper until you have finished analyzing your results and prepared the figure that summarizes your results and compares them to a theory. (Note that graphs and diagrams are both called figures in technical papers.) You may have more than one such figure; in any case, prepare all the data figures before writing a word.

Let’s say you are writing about the pendulum experiment. You will probably have (at least) a figure that shows the experimentally measured length dependence of the period and a comparison with a theoretical function. Your data will be carefully plotted (see Fitting Data) with uncertainties represented by error bars, axes carefully labeled, the fitted curve on the plot, and the fit results copied down for inclusion in the figure caption. You may also wish to add "residuals" to your plot. Plotting residuals zooms in on the agreement (or disagreement) between your data and the theory.

This plot is the kernel of your assessment of the length dependence of the period of a pendulum and organizes the paper your will write about the experiment. Everything you put in the paper before this figure appears works to prepare the reader to understand what is plotted in the figure. Everything that comes after explains the results and conclusions you obtain from the figure. That is why you cannot begin to write the paper until you have the figure.

Now that you have a nice figure and you have analyzed your data, your goal is to write the introduction, theory, experiment, and results sections that provide the background we need to understand your figure. At the end, you write a conclusion that shows what your result(s) mean in the grand scheme of things. Finally, write a brief, tight, quantitative abstract that summarizes the most important point (or points) of the paper.

Style

In The Elements of Style, Strunk and White suggest using the active voice as much as possible. This is a worthy goal in scientific writing, but often the role of the investigator is irrelevant to the topic at hand. Let me illustrate. Compare the following descriptions:

By running a current through a coil of wire, we can produce a magnetic field which will deflect the needle of a compass. When we have done this, we can take a bar magnet and position it such that the needle is no longer deflected. Once this has been done, we need only to measure the distance from the needle’s center to the magnet. Using this and the properties we have already measured from the magnet and the coils, we can calculate the current through the loop. Because we only took measurements of mass, length, and time we have determined a value for current not based on any other electrical or magnetic quantities.

Hans Christian Oersted discovered in 1820 that a current flowing in a wire generates a magnetic field proportional to the current.¹ By comparing this field to that produced by a calibrated permanent magnet, and by using a geometry in which the constant of proportionality between field and current can be readily calculated, it is possible to measure the current–an electrical quantity–by measuring only the mechanical quantities mass, length, and time. K. F. Gauss first proposed a technique for making such an absolute determination of current in 1823.² We report here a modification of his technique which yields current measurements having an accuracy of 1%.

In my opinion, the use of the first person in the first paragraph does not add useful information; rather, it detracts from the message that these phenomena exist independent of the observer. The second paragraph uses some active voice and some passive voice, throws in some historical information, and keeps the discussion conceptual, as befits an introduction.

Make no mistake: good writing of any kind, whether technical or not, requires practice and a willingness to rewrite. Simply put, it’s hard!

Use figures. Think carefully about how to display your data to fullest advantage. Figures are used much more frequently than tables in scientific publications, but sometimes a table is just right.

An abstract should be as informative and quantitative as possible. It should summarize the important finding(s) of your work. An example:

The speed at which light propagates through air at standard temperature and pressure was studied using a time-of-flight technique. A value of (2.995 ± 0.003) ¥ 10⁸ m/s was obtained, with the dominant error arising from the bandwidth of the oscilloscope used to observe the light pulses. This value is consistent with literature values for c and the refractive index of air.

Pitfalls

• Avoid imprecise, vague, or unclear language. Carefully define your terms and use them consistently. Avoid jargon and excessive abbreviations.
• Do not fail to tell a story. Organize your information so that the narrative proceeds smoothly and logically.
• Do not repeat every sordid detail from a lab diary; report the logically crucial ones.
• Use SI units unless there is a compelling reason not to. That is, use mm or nm, but not Å.
• Do not distort unpleasant realities; call it like it is. Don’t attempt to cover up flaws in your data; do explain departures from theory when you can.
• Figures are used much more frequently than tables to display data. A well-made graph speaks volumes. If you are sure you need a table to display some data in a paper, clear it with a professor.

Updated 8/26/00 by Peter N. Saeta .