Fall 2000

Physics 516 / 616 - Intermediate / Advanced Laboratory
Laboratory Write-Ups

No piece of scientific work can be considered as finished until the experiment is described and the results and pertinent thoughts of the worker are recorded on paper in such a way as to be intelligible to qualified people. One generally finds that at least as much effort is required in this phase of an experiment as is necessary in its planning and execution. It is not a simple matter to express oneself in a style which is logical, unambiguous, comprehensive, and relevant. To achieve such a style, one must devote a great deal of persistent effort to the writing, and must develop a critical attitude toward one's own work.

These, then, are the objectives in the write-up: first the reader must be oriented so that he or she may readily understand your presentation. This may be done through a proper Introduction, which forms a link between the reader's broad general knowledge of physics and the specific experiment upon which you wish to report. The next section, which we might call Experimental, should tell the reader in relevant detail what was done, the procedures, the observations, the precautions and the conditions under which the experiment was performed. This might be followed with a section called Results, which presents the results in such a way that the reader can grasp them quickly and easily. Finally, you may conclude with a part on Discussion and Conclusions.

The following is a list of what is expected in a laboratory report:

  1. A statement of the objectives of the experiment.
  2. An outline of the procedures you followed.
  3. Sketch or diagram of the equipment, showing the setup with major pieces of equipment unambiguously identified.
  4. List of the equipment.
  5. A discussion of the measurements you performed and your observations in performing these measurements. Also a discussion of how you know what the uncertainties on the measurements are.
  6. All of the raw data in table form, clearly labeled including estimates of experimental uncertainties.
  7. All formulae used. Try to derive or justify (by reference) the ones you use.
  8. Analysis of the data, including sample calculations, and final results with errors derived or justified using some sort of statistical analysis.
  9. Graphical representation of results.
  10. Conclusions and discussion of the experiment.
  11. List of references.

Below, a more detailed examination of some of the various sections is given.

The Introduction

One of the main functions of the Introduction is to motive the reader. Remember that the prime objective in scientific writing is to inform the reader of something which he or she wants to know. In the Introduction you must influence the reader by telling why, if one is to understand the subject to which your write-up is a contribution, one must read and understand your paper. The Introduction has a further function: it should provide an orientation to prepare the reader for the information you are about to give. This may be accomplished by a brief but broad review of other work which has led up to your own, its significance (where it fits into the overall subject of physics), and perhaps a very short statement of the contribution to the field which might be expected from your own work, i.e., what you hoped to show by undertaking the work. It is obvious that one has a wide choice in his approach to these objectives; the choice involves not only what is to be included in the Introduction but what is to be postponed to the body of the paper, or indeed left out altogether.

It is helpful to notice the kinds of things which writers include in the Introduction by reading the scientific literature. An excellent place to begin your reading of Introductions is in "The American Journal of Physics". Current issues are on the shelves on the second floor in the Science and Engineering Library . Notice, during your reading, the opening sentences. A good opening sentence should form a bond between the reader's past experience and the work you intend to present.

Experimental Section.

In this section describe in language as simple as possible, but logically organized, what you did. You cannot describe (nor does the reader want to know!) everything that you did. Some details - like the need to dust off the equipment or find an extension cord to plug it in - are not necessary in a formal lab report, even though they might be written down in your notebook. You should abstract those things which were significant, keeping in mind the primary objective of informing the reader of what he or she must know to understand the experiment. This takes a great deal of thought and judgment. It may be appropriate to discuss the pros and cons of the particular apparatus and method used in this lab, in terms of their suitability for detecting the phenomenon being studied and for obtaining a desired accuracy and precision.


Your data may be presented in several ways, but rarely in the exact order as you took them. Your objective must always be clarity and comprehensiveness. If the data are few in number perhaps a tabular form will be the most satisfactory. Be sure that you lead the reader from the description of the experiment into the presentation of the data. Tables should be numbered, so one can refer to them in the text, should have a suitable heading which make the table intelligible without the necessity of flipping back through the text, and should have a heading for each column.

It is usually wise to represent the data with a curve. In this case the individual experimental points with their error bars should be shown, together with a smooth curve representing the relation between the coordinates. Number all graphs so they can be referred to in the text, label the graph in such a way that it is intelligible without the necessity of flipping back through the text, and label both axes. Sometimes the curve will be the best smooth curve through the experimental points; sometimes it will be the curve given by the theory being tested with the experimental points for comparison. Sometimes both will be shown. Graphs should be scaled in such a way that the curve occupies a good fraction of the sheet of graph paper, i.e., is neither an almost horizontal or vertical line nor all concentrated in one corner of the sheet of graph paper.

Discussion and Conclusions.

This is the "pay off" of the experiment. Here you will be concerned with your success in demonstrating whether or not the theory being tested coincides with the facts. Experimental error then becomes a prime consideration and you must determine by logical means the dependability of your data so they may be compared intelligently with the predictions of the theory. Here, too, the shortcomings of your experiment should be discussed, together with their effects on the results. You may wish, also, to discuss the implications of the theory which is supported by your experimental results in explaining an aspect of the physical world.

General Hints.

One must keep firmly in mind in scientific writing that the overriding objective is to inform the reader, i.e., to formulate the same thoughts in the mind of the reader as those which were in the mind of the writer. This means that the writing must have logical structure.

The logically of a paper or write-up is easily tested. Each sentence should inform the reader of something he or she should know in order to understand the experiment and to find its results useful, all in a manner so clear and in such simple language that the reader cannot be mistaken, provided, of course, he or she reads the words exactly as they are. Each sentence should follow naturally from the sentence before, that is, should be demanded by it. A rough rule-of-thumb test is to put your pencil on an arbitrary period and notice whether any statement made before that tacitly assumes something which you will only tell the reader afterward. If so, there is a non-sequitur in your writing.

Ambiguities are among the most difficult faults to eliminate. Short sentences are helpful. Proper qualifying adjectives and adverbs are essential. In the end the elimination of ambiguities depends upon your skill as a writer in "putting yourself in the shoes" of the reader to anticipate and remove each potentially ambiguous point by choice of organization, a clarifying sentence, an adjective inserted in the right place, or other means. Having a classmate or instructor read your draft and make suggestions before you turn in the formal report may be helpful, both for removing ambiguities and for improving overall organization.

Practical considerations and Record keeping.

The data which you take and the notes you wish to make during the execution of the experiment must be entered directly into your notebook. This is standard laboratory procedure, not only in universities but also in industrial and government laboratories. In fact, many times lab notebooks are important pieces of evidence in patent disputes. So get in the habit of keeping an accurate, dated record of everything you do in the lab. Your notebook should be so detailed that it would allow you to reconstruct your experimental set-up and procedure, even after time has passed.

Late Penalty.

There will be a penalty of five points per day for lab reports turned in after the due date.