The purpose of your college lab reports is for you to practice writing the reports that will compose your career. Science and engineering majors will write many of these reports after they graduate, but very few students with physics requirements will never need to publish a science report in a long career. The lab report is your opportunity to show the lab instructor that you have learned this essential skill and to keep this skill fresh. Because of this, there are some things to keep in mind that will help you out when your report is graded.
Make your lab report easy to follow. Show how you get from one statement to the next. If a value is particularly important, put a box around it. Don't go overboard! We're not looking for reams of paper here; in fact, the shortest reports are often the best reports. Just make sure that someone who hasn't done the lab can understand what you did and how you did it. Including the correct material is required and will gain points, but we disregard extraneous stuff. Pretend your audience is familiar with science generally, but has not performed this experiment. Later, STEM professionals worldwide will read your reports, so pretend you are writing to that audience now.
Believe in your data. Contrary to popular opinion we do not consider how close the value you obtained agrees with the one in "the back of the book" when assigning grades. If you are supposed to verify a law of nature, and you end up disproving it, that's fine, provided that you say that you disprove it. If however, you cannot verify it, but say that you can, we can only assume that you didn't understand the experiment. If your results are completely different than established values, then you have probably measured or calculated something incorrectly. These mistakes will warrant deductions; don't make it worse by altering data or by lying about what your data say.
Follow a well thought-out format for your lab write-up. We don't expect something publishable in the Physics Review Letters, but on the other hand, we don't expect four pages of stream-of-consciousness writing either. A sample 'IMRaD' format follows:
Tell us what your experiment is.
Tell us your name and your partner(s) name(s).
What purpose(s) does this experiment serve to STEM? What hypothesis is the experiment designed to test? All that follows should serve this Introduction.
Describe/illustrate your entire apparatus. Schematic/block diagrams are useful. What sequence(s) of setups/measurements did you perform? Where do you report your data/results (name the table, figure, etc.)? What analysis did you do?
Present and discuss your raw data -- including units and uncertainty estimates where appropriate. Discuss computations, graphs, and other results from the raw data. Record and discuss any expectations and/or independent observations.
Summarize and explain what your data imply (about your purpose and hypothesis). Report physical constants that you measured. Are your results consistent with theory and/or previous measurements? Discuss this and any likely cause(s) of disagreement.
As you are writing your Discussion, it might pay to glance at the Introduction. Did you succeed in what you set out to do? Why or why not? Conversely, you might look in your Discussion for ideas to write in your Introduction. Also review your Data and Results for measured physical constants that are worth emphasizing in your Discussion. Pick the best one that YOU measured to mention prominently.
Mention anything else that you have learned from the lab, even if it doesn't seem to be directly relevant. For example, noticing that Teledeltos paper might be useful in sending pictures by teletype wire. Another suggestion that sound resonance in a tube is similar to a driven RLC circuit might be noteworthy. If someone is paying so much attention to the lab exercises that (s)he notices this sort of thing, this will reflect in his(her) grade. On the other hand, this is not at all mandatory. Most labs are very straightforward with no hidden meaning at all, but, if you see a potential application for an item, a strategy, or a result, this indicates that you have been paying attention. Even if you miss a point your grader was expecting, it is likely that (s)he will substitute points for this evidence that you were engaged.