Laboratory reporting is an acquired skill. Below some remarks that are general to the lab reports, with some examples based on the first experiment with Michelson's Interferometer.

Contents:

1. Logging the Experimental Data
2. Laboratory Report Writing
3. Common Mistakes and How To Avoid Them!

Logging the Experimental Data

• First, you need to log carefully all details of the setup, the experimental conditions, and the procedures you followed. Note the time-of-day for the various measurements, and all relevant environmental and experimental information (e.g. atmospheric pressure in the Michelson-Morley experiment, thickness of the windows of the pressure cell, length and its uncertainty of the cell, etc., etc.). This is absolutely crucial if you later on want to analyze the data, reconstruct what went awry, or deduct and estimate possible sources of errors.
• It is strongly recommended to read the lab note some days before doing the experimentation, and to try to understand the purpose and procedures in advance. A way to do this is to go over the next laboratory with your partner at the end of the current laboratory session. Discuss what the quantities are that you want to find, and all measurements and input numbers needed towards the final result. Estimate which data inputs are most critical in terms of precision of the final result.
• During the lab you should check your data regularly with back-of-the-envelop calculations to see if the results obtained are within expectations, and not wildly off.
• Have the TA sign-off on your data in your logbook before leaving the lab.

Laboratory Report Writing

• Follow the basic rule of dividing the report up in concise sections. e.g.:
  Title (plus Author, date), Abstract, Introduction (history, goals), Experimental Setup (apparatus description and sketch), Data Taking (data tables, procedures, uncertainty estimates, etc.), Data Analysis (calculations and derivations), Result(s) and Discussion (results and significance, comparisons with other results), Summary, Acknowledgements, and Bibliography (all references used).
• Show UNDERSTANDING: Why does the experiment work, what is its underlying physics principle, its function, its goal? Why is the instrument built and used as it is? What are the advantages of the meths used? What is so elegant about the principles used? e.g. for the first laboratory (the Michelson Interferometer) discuss and answer the following:
  • Why use a laser?
  • Why a half-silvered mirror? Need it be exactly at 45^°? What is the ideal transmissivity?
  • Why split the beam in the first place?
  • What is the function of the lens?
  • How can the knob read mm's and still show a regular screw thread? (a regular thread has a speed of order 0.5 mm)
  • ....etc....
• Derive the physics formulae used, and/or explain where they come from; e.g.: l = 2d_m/m .
• Discuss both STATISTICAL and SYSTEMATIC errors! Read the error analysis handout!). Estimate the dominant source(s) of error and try to minimize your experimental error (or at least indicate how you would, if you were to re-do your experiment).
  Any discrepancy between a generally accepted value and your measurement is NOT AN ERROR but either an indication that you have not fully understood all sources of error in your measurement, OR that you made a new discovery! Don't come up with non-sensical speculations of why your result doesn't agree with the accepted value. Do not artificially increase the error estimate on your measured value to make it agree!
  e.g.:
  In the first lab the micrometer knob is not very well calibrated: the shift in the moveable mirror is not precisely the shift indicated by the knob! (Never trust a knob!) Also, there is probably some play in the mechanism: changing the direction of turning will often lead to very different results (in terms of fringes/mm). Such "play" can be avoided by consistently turning the knob during measurement in one direction only!
• Discuss the procedure only shortly, do not copy the manual (but you may refer to it); I know what is in the handout myself! Do discuss, in your own words, the principle of operation of the setup and/or problems you experienced. e.g.:

  ``the Michelson interferometer measures differences in pathlengths to a fraction of a fringe (that is, to a fraction of a wavelength) by comparing an "undisturbed" wave, with one that is "perturbed", e.g. by the insertion of a pressure cell whose pressure can be varied. In this way very precise measurements of distance differences can be made ...etc...''.

• Check spelling and syntax. This works best if you use a Word Processor. If you haven't used one yet, start now: you'll quickly experience the many advantages, and not only for physics! Computers are reasonably cheap nowadays (below $900 for a starter model), and students have access to computers in the main library and the many SINC sites on campus (ask the relevant offices, or the undergraduate studies office in the main library for access requirements and computer accounts).
• For data analysis and graphing you may want to use a Spreadsheet program. This allows for sophisticated plots and even for linear or polynomial fits to data sets. Be prepared to spend a significant amount of time in learning to use such a program if you haven't before!

Common Mistakes and How To Avoid Them!

• State clearly and succinctly what the idea of the measurement is. What is the physical principle behind it? And how did you apply it to measure the quantity you are interested in? Do not need to give a long, historical introduction.
• When you explain the setup, do not enumerate the equipment, but describe its functionality and use. Discuss why this is the only, best, or simplest way to measure the quantity of interest.
• State (and derive if requested) every formula you use in your evaluation and then list the values you insert insert (with their uncertainties), otherwise we will probably be unable to tell what you have done.
• You should apply error propagation formulas. However, don't apply them blindly, and make sure the uncertainties in your measurements are sensible. Record the uncertainties in your data together with the data itself.
  Note, that the deviation of your results from the theoretical or the accepted value is not the error in your measurement!
• Use units throughout your calculations, and not only for results! This helps to trace mistakes in the calculations: if there are different units on the two sides of an equality, something is clearly wrong.
• If you have problems or questions, by all means, see the TA during his lab or office hours! Don't wait until it is too late.