Writing Lab Reports
Purpose
The purpose of a scientific report is to make the results available to others. The contents of a laboratory notebook are rarely suitable for communicating the aims, procedures and results to another scientist, so publishing scientific papers is the normal way of making the outcomes of scientific investigations available to others.
General advice
A report is intended to communicate specific information to a specific audience. It's important to decide on the purpose of the report and be consistent with this purpose from the title through to the conclusion. For example, is the report giving a value for the acceleration due to gravity, or describing a new way of measuring g?
A good tip is to write with your audience in mind. For the reports you will write as part of your degree program you should assume your audience is an undergraduate at about the same level as yourself, but who has never seen or heard about the experiment that you performed.
A report represents your final considered opinion on an experiment, and for professional scientists, is the only thing that most readers will see of your work. For this reason, it has to be absolutely correct.
Note: The report should include a full explanation of the estimate of precision. This is where your laboratory reports will differ from a standard scientific report.
Structure
The report should be a continuous piece of prose. Extra information such as tables, figures and appendices should be referenced in the text ('figure 1', 'table 1', etc.) and included in the report as close to the reference as convenient.
A report should consist of:
- Title
The title should clearly indicate what the report is about, without being too long. Don't use the short titles used in the laboratory to identify the experiment. For example, 'Young's modulus' doesn't even tell the reader if the report is a theoretical calculation or the result of an experiment.
- Abstract
The abstract is often the most widely read part of a paper and should be a summary of the entire report, including numerical results. It should set out the aims, results and principal conclusions in a few sentences. Despite being the first main content of a report, it is often the last thing to be written. This is because it is a summary of what was actually said in the report, not what was originally planned to say, which may have changed through the various drafts and revisions.
- Introduction
The introduction should describe the purpose of the experiment, give enough 'background' to set the scene, and set the experiment in the context of physics as a whole. You don't need to describe the apparatus in detail but you could mention the general principles.
- Theory and description of the apparatus
These may be two sections or a single section. It can be difficult to choose which to describe first - the theory may not be clear without a description of the apparatus but the operation of the apparatus may not be clear without a description of the theory.
- Procedure
Experimental reports are usually written in the passive voice, i.e. 'the length was measured'. Although rarer, it could also be written as 'I measured the length'. Note that the past tense is always used.
Mathematical equations should be included as part of the grammatical structure of the sentence:
'The area, A, is given by
(6), where a and b are the x-coordinated of the two wires.'
The (6) is used where the equation is referred to in the text of the report.
Theory can be summarised in the procedure section, but well-known equations don't need to be derived. - Results
The results section should not consist solely of numbers. It should be written in normal paragraphs, and include critical values and a description of how the results were analysed. Results of the error analysis should also be presented and incorporated into an overall uncertainty for the final results. All numerical data should be in S.I. units with the correct abbreviations.
Your reports will differ from a standard scientific paper in two ways: Firstly, the original results should be included in a table in an appendix. This allows a marker to check your calculations. All readings relevant to the final result should be included, including calibrations, etc. Secondly, full details of the calculation of the errors is also given in an appendix.
- Conclusions
The conclusion is the other main section of the paper that is likely to be widely read. Give your final numerical results here along with their uncertainties. Compare these if possible with values obtained by other authors, and make substantiated comments on any discrepancies. State conclusions about other relevant information given by the experiment, describe any major difficulties and give suggestions for improving the experiment.
- References
Give references to textbooks and papers that you mention in your work. A well-known piece of theory doesn't need to be repeated but a reference can be given so that readers can look it up. References are usually collected at the end of the text before the appendices. The reference should have the following format:
- Serial number. This is the number given when the material is referred to in the text, e.g. [5].
- Author(s) surnames and initials.
- Title. The title of a book should be given, including the edition number if applicable. For a journal, the title of the article, the title of the journal and volume number should be given.
- Date of publication.
- The page numbers. This should be the specific pages for a book, or the page range for an article in a journal.
- Appendices
Some material is placed in appendices to avoid breaking the flow of the report, e.g. algebraic details of theory. A reference should be made in the main text ('See appendix 1') so that the reader knows that the extra material is available.
- Graphs and diagrams
These should be referred to as 'figures' and numbered consecutively. Each figure should be placed in the text at an appropriate place with a short caption and referred to by number in the text.
Diagrams should be neatly hand drawn or computer generated. Labelling should be linked to the diagram using short lines and arrowheads, rather than being drawn directly on the diagram itself.
Graphs should have the axes at an appropriate scale and properly labelled. Error bars should be shown if applicable. The controlled (or independent) variable is normally along the x axis and the dependent variable along the y axis, although this is not a hard and fast rule. For example, if we were plotting light intensity against water depth it would make more sense for the vertical axis to be used for depth (with zero at the top) and the horizontal axis for light intensity.
Other resources
- An example of the grading sheet for lab reports is available.
- University advice on citing references using the Harvard system can be found here (pdf, 99 kB) and here (pdf, 77 kB).