You should write a section on the theory behind your experiment. Do not mix your results or interpretation into this section, which should be 2-4 pages. Experimental Methods and Procedures Include at least one clear diagram of the experimental setup. Be sure to describe your experimental methods in detail. The length of this section will depend on the experiment that you did, but as a guideline, it should be between 3 to 5 pages.
Detailed figures add a lot to the clarity of such descriptions.
Results Tables are great for summarizing results. In some cases, graphs are preferable to tables, since they make it much easier to see relationships in the data. In fact, a lot of students miss important observations because they don't bother to graph their data. Be sure to include a discussion of how you estimated your experimental uncertainties in the raw data and how you propagated these uncertainties into your final results. Discussion and Interpretation I prefer to have the interpretation of the results in a separate section from the results themselves, since it explicitly separates what you measured from your interpretation.