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:
- A statement of the objectives of the experiment.
- An outline of the procedures you followed.
- Sketch or diagram of the equipment, showing the setup with
major pieces of equipment unambiguously identified.
- List of the equipment.
- 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.
- All of the raw data in table form, clearly labeled
including estimates of experimental uncertainties.
- All formulae used. Try to derive or justify (by reference)
the ones you use.
- Analysis of the data, including sample calculations,
and final results with errors derived or justified using some sort of
statistical analysis.
- Graphical representation of results.
- Conclusions and discussion of the experiment.
- 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.
Results.
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.