9. LABORATORY RECORDS AND REPORTS

by Dr. Donald E. Simanek
Lock Haven University

9.1 PREPARATION FOR THE LABORATORY

  1. Read the instructions before coming to lab. If you have not received instructions at least one week before the lab period, ask your instructor to supply them.

  2. Read the relevant background material in your textbook, or in library references.

  3. Come to laboratory with a plan in mind, and at least a preliminary derivation of the error propagation equations.

9.2 THE LABORATORY RECORD

Scientists and engineers record laboratory data in bound notebooks with pre-numbered pages. These books serve as a permanent record of the work, and can serve as legal evidence in priority disputes. Some instructors insist that students in science laboratories keep such notebooks. Whether required or not, the use of a notebook helps you to develop good laboratory habits that will serve you well in your future career.

Your laboratory notebook reflects your personal style, but you should write it so that a co-worker familiar with the subject of your research could understand it. Such a person may need to obtain information from your notebook. You may need to refer to the notebook at a later date, therefore do not omit any information necessary to understand what you did, or to repeat it.

Use a bound (not a loose leaf) notebook for the laboratory record. Make notebook entries as the experiment progresses, as a running record of the work. The notebook includes a complete history of all experiments performed, and their results.

Quadrille-ruled pages with 1/4 inch squares facilitate making data tables and rough graphs. Don't erase anything in a laboratory notebook, and never remove pages from it. Line out, and annotate, mistakes. Use permanent ink, for better readability. You may abbreviate, but make all entries clear, organized and complete"and neat enough for you, or someone else, to read.

Here's a check list of items which you should record in the notebook:

  1. The date and time of each new record.

  2. The initials of the person making the record.

  3. Descriptive headings, titles, and subtitles.

  4. Lists of the equipment used (name, manufacturer, model and serial numbers), with relevant specifications.

  5. Sketches of the experimental layout, circuit diagrams, etc., with all components labeled.

  6. Observed data. Record data in the notebook immediately; do not recopy it from scraps of paper. Organize the data in neat tabular form, with ample space for corrections and auxiliary notes. Symbols and notation of each column heading should match that used in the equipment diagram, equations, and other references in the discussion. When possible, identify the exact instrument used. Neatly line-out incorrect data. A large amount of incorrect data may require you to line-out (or overlay with a large X) an entire table. If you feel that an 'X' across a whole page looks unsightly, use a footnote to label it as "deleted." Always record the reason for such altered entries.

  7. Calculated results, prominently displayed.

  8. Sample calculations. Don't include every calculation, but do include a sample of each type. If you need to do this same sort of calculation later, the sample may save you time.

  9. Curves. Plot tabular data as curves whenever possible.
    We use the term "curve" to represent data points plotted with a smooth line drawn through them. The term "curve" applies even to straight lines.

    The term "plot" refers to roughly sketched curves, perhaps done on the quadrille paper of the lab notebook. The term "graph" refers to the more neatly produced and annotated curves done on genuine graph paper, or in a form suitable for publication.

    Important data may deserve a graph made on genuine graph paper, permanently attached to the notebook page. Avoid using tape, for it deteriorates with age. Use a thin line of glue to "tip in" such added material. Attach charts, diagrams and photographs in the same manner.

  10. Graphs: All graphs (and plots) must have a descriptive title, each axis labeled with quantity, symbol, and units. Choose a scale size such that one may read values from the curves with at least the same accuracy as the accuracy of the data. Make the data points very small (some use pinpricks) and emphasize them with small, neat circles. When you show several curves on the same graph, group related data points in some way using distinctive symbols, such as circles, triangles, and squares (use a symbol template, for uniformity). Provide a key, on the graph page, to the meanings of the symbols.

  11. Notes or explanations essential to proper performance of the experiment or interpretation of the results. This might include your explanation of how you overcame any difficulties encountered in the experiment.

  12. A restatement of the questions posed, and your answers.

The reader won't expect the lab notebook to contain a condensed and polished report of the experiment, but will expect to find enough evidence to determine what you did, how you did it, and what results you obtained.

9.3 THE LABORATORY REPORT

Disorganized reports annoy and confuse the reader.
© 2001 by John C. Holden.

The laboratory notebook provides a personal record documenting the progress of the experiment. The laboratory report serves a quite different purpose. It communicates your experimental work to other persons. This demands a different style and approach.

All "real" scientific work of any value (and some that isn't) eventually finds expression in a written report. In industrial research and development, reports communicate to supervisors and directors, may circulate internally within the company, and may even reach other scientists in the same field around the world. Some reports get published in technical and scientific journals. Even technicians sometimes write reports.

Many a scientist or engineer discovers the hard way that people judge the quality of experimental work by the quality of the reports. Ineffective reports may cause people to ignore the research itself, and, on a very practical level, may jeopardize the funding of that research.

Style and appearance of reports:

  1. Use good quality standard size 8 1/2 by 11 inch paper: plain, unlined, and with no holes or ragged edges. (Some instructors may accept handwritten reports on lined paper, a practice considered unprofessional in a real work situation.)

  2. Leave at least a 3/4 inch margin on the top, bottom and sides of the sheets.

  3. Organize the report for easy reading. The structure and organization of the report should impress itself on the reader even with a casual skim. Use headings and subheadings to make the structure clear.

Essential parts of the report:

Here's a list of the usual parts of a complete report. The nature of the experiment will determine which ones are necessary, and the appropriate heading for each.

  • ABSTRACT. A brief (one paragraph) summary of the purpose, method, and significant results of the experiment.

  • PURPOSE (OR OBJECTIVES) OF THE EXPERIMENT (Don't include this if your report has an abstract.)

  • EQUIPMENT LIST, including any identifying model and serial numbers.

  • BACKGROUND. A review/summary to acquaint the reader with facts, theory, or research specifically relating to what you did in this experiment.) Material readily available in any textbook needn't be included.

  • MATERIALS, METHODS AND PROCEDURES. This tells the reader what specific experimental methods were used. Apparatus or procedures unique to this experiment must be described and explained. Standard procedures needn't be elaborated, by should be referenced.

  • RESULTS, including graphs, and tables of results, as appropriate.

  • DISCUSSION OF RESULTS, and of their uncertainties.

  • CONCLUSIONS (You may prefer to include this in the discussion of results.)

Avoid unnecessary duplication. Don't include data and procedure in the results section. Don't include minor details of procedure, theory and results in the abstract. Include only material directly related to what you did in the experiment. Omit idle speculation.

9.4 FORMAL AND INFORMAL REPORTS

The informal report differs from the formal report in three major respects. The informal report omits: (1) the abstract, (2) description of procedure (except where there were significant deviations from the procedures of the instruction manual), and (3) exposition of the physics underlying the experiment.

Your instructor may want a copy of your laboratory record included as an appendix to the report, for completeness. This will include the equipment list, original data, calculations, preliminary graphs and sketches, record of observations made in the laboratory, etc. The instructor may, in the informal report, allow you to insert this after the "purpose" section of the report, to preserve chronological continuity. Don't expect that anyone will necessarily read this! Whatever you want the reader, or instructor, to consider in evaluating your work must appear in its appropriate place elsewhere in the report.

9.5 GENERAL CONSIDERATIONS OF REPORT WRITING

A real experiment may occupy months or years. The laboratory record may consist of several filled notebooks, computer printouts, photographs, charts, etc. You must distill, reorganize and repackage this scattered source material into a clear and concise document of a just a few pages. The report must communicate efficiently. It must have a clear and logical structure which allows the reader to extract the essential points easily.

Readers of your report want to know what you accomplished, and you must say that clearly and effectively. Every experiment has certain objectives, and you must state the extent to which these were accomplished. If you set out to determine the constancy of the acceleration due to gravity, you must, in your discussion of results, state whether your experiment demonstrated its constancy, and within what uncertainty. If you set out to measure the size of the acceleration due to gravity, you must give your one best determination of that acceleration, along with its estimated uncertainty. These statements must appear in the "results" section, even if they appear elsewhere in the report.

  1. Condense and prune the presentation to make your points effectively. Emphasize the important points. Don't waste the reader's time with trivia.

  2. A good rule for improving your prose is:

    WHEN IN DOUBT, LEAVE IT OUT!

  3. Don't clutter the text with calculations unless you must explain something about them.

  4. Don't pad the text. Readers don't appreciate having to read through trivial and irrelevant passages to find the important parts.

    ESCHEW SPECIOUS PROFUNDITY!

9.6 GRAPHS

  1. Use genuine graph paper, not cheap substitutes. Every graph must have a title, written out in words. Not: "T vs. L." Not: "Period vs. Length." Rather, something more specifically descriptive, like: "Pendulum period as a function of suspension length." Choose the size of the axis scales so that the graph nearly fills the page.

  2. Label each graph axis with the quantity, symbol, and units plotted on that axis. Example: PERIOD (T) in seconds.

  3. Label the axis scales neatly and clearly. You must re-label logarithmic scales on commercial log paper.

9.7 TABLES

  1. Use tables for large amounts of data, especially when you wish to display the relations inherent in the data.

  2. Column headings of tables must indicate quantity, symbol, and units, just as graph axes do. Each table must have a title and an identifying number, for reference.

  3. Indicate the errors (uncertainties) for all quantities. Minimize the clutter within tables by grouping information when possible. If all data entries in a column of a table have the same absolute or relative error, put that information at the top of the column only. The same applies to unit labels, which you may place at the top of the column.

9.8 DISCUSSION AND ANALYSIS OF ERRORS (UNCERTAINTIES)

  1. Show how you arrived at your uncertainty estimates.

  2. Show the error propagation equation(s) you used. Error propagation equations motivate decisions about experiment design and procedure. They also justify the uncertainties you assign to results. If some error sources dominate others, this fact may deserve comment. Tell how you designed the procedure and strategy to minimize uncertainties. [You need not mention the usual precautions; only those specific to the particular experiment, or in some way unusual.]

  3. Make meaningful comparisons where appropriate. When the experiment has numeric results that you can compare with other independent sources, comment on that comparison. Do not call this comparison the "error", call it the "experimental discrepancy." When you can quote both error and discrepancy, do so, and comment on their relative size. (A discrepancy larger than the error certainly requires some comment!)

  4. The methods of science never prove anything. The word "proof" refers to a strictly mathematical process. Nor does science claim absolute truths. Avoid the word "truth" in scientific discussion. In a single experiment you might "verify" or "confirm" the validity of a physical law, in a particular situation.

9.9 DISCUSSION OF RESULTS, AND CONCLUSIONS

  1. Your conclusions must relate to your stated purposes or "objectives". Tell the reader to what extent your objectives were realized.

  2. Don't claim more than the facts warrant. Support your assertions with evidence, logic, or specific references to the literature. State specifically what you achieved, and the estimated uncertainty of the results, but don't make broad and unfounded generalizations.

YOU CAN'T EXPLAIN SOMETHING TO SOMEONE ELSE
IF YOU DON'T UNDERSTAND IT YOURSELF

9.10 ORIGINALITY

Students benefit from study groups, learning from each other. Strongly resist the temptation to rely too heavily on others. When exam time comes, you must work alone.

Laboratory partners discuss each experiment and share ideas. But in a classroom situation the written report represents your own work, not that of a committee. Don't let others do your thinking and analysis.

Partners' data will, of course, consist of the same sets of numbers, but each partner will organize the report to suit his or her own personal tastes and style. Each will do the data analysis independently. Partner's reports will, therefore, not look alike, even superficially. When partners make identical mistakes, this raises suspicions that one must have copied without thinking. Plagiarizing something wrong or absurd makes one appear not merely unprofessional, but also thoughtlessly lazy! Signing your name to a totally wrong statement copied word-for-word from someone else demonstrates your inability or unwillingness to think the matter through on your own. Better to make your own mistakes, honestly. Better yet, use critical thinking to discover your mistakes, and those of others.

When you write the discussion of results yourself you'll gain the valuable experience of drawing your own conclusions, unprejudiced by the opinions of anyone else. All details of the report will reflect your individual style and individuality.

9.11 THINGS YOU SHOULDN'T DO

Don't include idle speculation about sources of error. To say that certain conditions of the experiment "may have caused error" communicates no useful information unless you cite some specific evidence or a plausible mechanism pointing to that fact.

Don't include such trivial comments as: "The resuslts may have "human error." We all know that human blunders, misperceptions, and misinterpretations can occur. We expect the experimenter to take every precaution to avoid them. This "goes without saying." The other classes of "human error" due to limitations of instruments, and limits of human observation of instruments belong in the quantitative error discussion.

Likewise, don't say "Error in results could arise from calculation errors." If you mean blunders, this statement tells us nothing we didn't already know (we still wouldn't know whether there were blunders). If you mean the error introduced by calculating devices, then you haven't done your job properly. Your responsibility includes choosing calculation techniques that do not introduce significant error. You should do everything necessary to keep calculation errors negligible compared to the experimental errors. If for any reason you did not, or could not, accomplish this, you must give good reason why you didn't.

9.12 STYLE

Most elements of good style common to other types of writing also apply to scientific writing. One of the best general references for the student is:

Strunk, William, Jr., and White, E. B. The Elements of Style. Macmillan Paperbacks, 1962.

This book demonstrates by example the clarity and brevity that it advocates. The 1918 edition may be found online and has internal links, which are very handy.

Other useful references are:

  • Menzel, Jones, and Boyd. Writing a Technical Paper.
  • Vallins. Good Writing, Better Writing.
  • Gunning. The Technique of Clear Writing.
  • Flesch. The Art of Plain Talk.
On matters of technical style for research journals, consult The American Institute of Physics Style Manual.

Examples of style faults.

We list below some faults frequently found on student laboratory reports, with suggestions for improvement.

    (1) A report organized as follows:

    "First we...
    Then we...
    Next we...
    Finally we...

      Aside from the overuse of "we" this "chronological" style doesn't convey any sense of the relative importance and logical connections inherent in the material.

    (2) "The acceleration of gravity, one of the most fundamental constants in physics..."

      This lacks content. It says nothing important. Stick to the facts and avoid empty generalities and attempts at "profundity." Also, gravity doesn't accelerate. This should read "acceleration due to gravity."

    (3) "In this experiment we proved the truth of the law F = ma and measured the value of the acceleration."

      This uses the words "prove" and "truth" in a questionable manner. Reserve "prove" for mathematical theorems. Avoid the word "truth" entirely in scientific writing. An experiment may disprove a law, but no finite number of experiments ever establish a law as absolutely true. The statement also leaves ambiguity: "acceleration of what?"

    (4) "We located the apparatus in the northeast corner of room 216 of the science building, in a sunny spot on a maple table 31 inches from the floor."

      Extraneous details annoy the reader. Include only those details you've shown to have some effect on the experiment. Some other details may deserve a place in the laboratory notebook, for future study may show that they weren't insignificant after all.

    (5) "I enjoyed this experiment very much and learned a lot from it."

      Save personal comments for other occasions. Don't include them in the laboratory report. The reader may easily misinterpret the motives behind such statements.

    (6) "Due to poor equipment we didn't get good results."

      No scientist ever has perfect equipment. The experimenter must learn the limitations of the equipment and how these affect the quality of the results. Sometimes experiments using very crude equipment have confirmed or rejected a law or theory.

    (7) Our results agreed exactly with the textbook value, so we consider the experiment a success."

      Even with the worst equipment and technique one may sometimes accidentally obtain a zero discrepancy. This tells nothing about the quality of the experiment. The limits of uncertainty tell us the quality of the experiment.

    (8) "A force of 9 kg stretched the spring 5 cm, therefore it did work (9)(0.05)(9.8)/2 = 22.05 Nt. From this we calculated the efficiency of the spring by..."

      Don't clutter the report with routine calculations. We don't fault the "force of 9 kg" in the first line. The context makes clear that the writer means "A force equal to the weight of 9 kg at the earth's surface."

9.13 LABORATORY ETIQUETTE

You and your partner will have an assigned work area or work station, which no one else shall disturb. Your responsibility includes keeping it in proper order. You will use equipment and parts stored in trays or drawers in an orderly fashion. Keep it in that order, for your own convenience, and out of consideration for other students who will follow you.

Keep your work area uncluttered. Store all instruments and components not actively in use in their proper place, away from your work area, or in the special storage cabinets.

You may need other equipment and components stored in a different area from your work station, perhaps in drawers or bins, or on shelves in the stockroom. Return these to their proper place immediately when you have finished with them.

Don't make unauthorized modifications to the equipment.

Don't use any kind of tape, markers, or ink on laboratory equipment.

Report damaged equipment or components to the laboratory instructor, for prompt repair or replacement.

[An E-prime document.]


Document © 1996, 2010 By Dr. Donald E. Simanek, Lock Haven University of Pennsylvania. It may not be sold or used commercially for profit without permission of the author. Teachers may freely use this document and distribute it to students without charge provided it includes this copyright notice.

The author welcomes suggestions for additions and improvement. Send to: this address:


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