Review Lab Techniques

Expectations for Physics 121L/131L/122L/132L/123L/133L Lab Reports

The purpose of the physics lab courses is to teach not only physics concepts, but also laboratory techniques of measurements and data analysis and communication skills. A well written lab report is key medium for the communication of laboratory results to the audience – in this case, the laboratory instructor. As lab reports need to vary from week to accommodate the requirements of a particular lab, there is no one way of writing them. However, there are elements of lab reports that are repeated frequently, and have general rules governing their appearance. The student is expected to follow these general rules when turning in a lab report to the instructor. Failure to do so, may result in a lower score/grade on the lab report.

Lab reports should always have the following information on the first page of the lab report: Name, Lab Partner’s Name(s), Date Experiment Performed, Instructor’s Name, Course Number, Section Number and Lab title. Write out the title in words, not just the lab or experiment number. If you are using the instructor provided data sheets, this information or space to fill in this information, is already at the top of the first page.
Data and/or Results tables. Data is displayed in table form. The table should be neat, with straight lines (drawn with a straight edge), a table title (word description, not just “Table 1”), and row and/or column headers labeled completely (ex: “mass, m (g)”). In the body of the table, you record individual values without units (units are found in the row or column headers) and rounded to the appropriate number of significant digits. Let me reiterate this – except in rare cases, only numbers go in the body of a table. The units go in the column (or row) header and apply to the entire column (or row). You can also put a common power of ten in the column (or row) header that applies to the entire column (or row) to more easily express very large or very small numbers. All measurements should be recorded to the appropriate decimal place to reflect the precision of the measuring device. For example, if you can measure to the nearest mm when using a ruler, a length of exactly three cm would be recorded as 3.0 (with ‘(cm)’ in the row/ col. header). Also, numbers with uncertainties should be rounded appropriately following the Rules for reporting experimental values (A-8, Appendix C, 121L/131L lab manual). See Appendix D of the 121L/131L lab manual for a discussion of data tables.
Graphs and/or plots. Graphs and plots should be neat and clear, with nothing on the back of a graph because it may show through the paper. Unless otherwise stated, you must draw your own graph(s) to submit with your lab report. Draw only one graph per page and take up most (or all) of the page in drawing your plot so the data is as spread out. Your axes do not necessarily need to go to ‘zero’. If they don’t, simply show a jagged line to indicate the gap. The graph/plot should have a meaningful word title that describes what is being shown. Both of the plot axes should be labeled (word description, symbol, and units in parenthesis) and numbered. If you are asked to draw a straight line fit, it should be drawn with a straight edge. When drawing a fit to your data, do not obliterate the graphed data points with your fit line (skip over the points if necessary). Unless told otherwise, you do not “connect the dots” when drawing a fit to your data. When calculating the slope of the line, do not use data points because they may not be exactly on the line. Instead, use two easy to read (e.g., located at the intersection of grid lines) and widely spaced points on the line. Draw a small box around each of the two points used to calculate the slope so they can be easily identified. Include your calculation of the slope with your lab report. If the origin is not included in your plot, you can calculate the y-intercept using the equation of a line (y = mx + b; wherem is the slope and b is the y-intercept. Use your value for the slope, m, and a point, xy, on the line.). You may put your slope (and y-intercept) calculation on your graph, in an unused corner, or include it on a separate sheet of paper with your other calculations for the report. Plots and graphs should be drawn on graph paper (unless the instructor allows or instructs you create the plot using a computer program). See Appendix E of the 121L/131L lab manual for a discussion of graphs.
Calculations/Sample calculations. Show a sample of any calculations you are instructed to perform for the lab. You must write out your own calculations and submit them with your lab report. Use your own data in the calculation, not an example shown on the board or in your lab manual. Be sure to include all units and uncertainties (when required) throughout the calculation. Make sure that the final result of the calculation is rounded to the correct number of significant digits if instructed to do so (or always for a number with uncertainty) and includes the appropriate units (always). Do not show simple calculations like averages or unit conversions unless specifically instructed to do so.
Questions. Questions should always be answered in complete sentences (unless they are only calculations or derivations). Questions are not assigned for every lab report.
Conclusion/Summary (1-2 paragraphs). The summary is like the conclusion of a scientific paper. A summary is brief overview – succinct (clearly expressed in few words). The paragraph conveys all the pertinent information without going into great detail. The details are in the data tables, plots, calculations, and the laboratory manual. The summary should start with an introduction sentence of what you did in the lab. What information was sought – what were the objectives of the lab (determine, calculate, and/or plot). What was the specific result or conclusion (the value, or that your data was well fit by a straight line fit as expected)? What does the result mean in terms of the physics? If you did not get the expected result, what things beyond your control might have affected your experiment (do not say “human error” – that tells the reader nothing)?

Some general advice

Always write in complete sentences. If asked to write a paragraph, do so. Do not use bullets or outline form unless you are specifically instructed to do so by the instructor.
Make sure your lab report is complete. Pay attention to the instructor’s lecture and data sheet (or other handouts) to see what elements are required for the lab report. The instructor may vary from the procedure or the requirements listed in the lab manual. If you are unsure of what elements are required in your lab report, ask the instructor. Incomplete or incorrect lab reports will be marked down.
Turn your lab report in on time.
Read the lab manual and any other required background material in detail before you come to class. You may not fully understand all of the details of the equipment until you see it in front of you, but you should have a general understanding of what will be required of you.
Complete the pre-lab early enough ahead of time to ask questions of the instructor (via e-mail, or office hours). Pre-labs are designed to help prepare the students to perform the lab and especially, to complete the lab and lab report within the allotted lab period.

CSU PomonaLast Update 09/20/12Dr. Julie J. Nazareth