A guide to writing a Physics 106/109 Lab Report This document contains a guide to what is expected of your lab report. You should read this carefully and follow the advice contained herein if you want to write better reports. If you have any questions at all, please email either your lab TA or me (Robert Schmitz). You can find email addresses on Blackboard.
Your report must:
– Be 100% your own work – Be typed, printed and fit on a single page – Have your graded lab data sheet attached – Follow the specific outline in the syllabus (Introduction, Results and Conclusion). – Be submitted at the start of the next lab session. Late reports will receive a grade penalty.
Before you print the report, run it through a spell/grammar checker and carefully read it through to see if you have made common errors such as omitting units.
If you haven’t yet done so, please take a moment to read through the example lab report, which is also on Blackboard. In this document I will use that example extensively to illustrate what is expected of you.
BEFORE YOU EVEN GO TO LAB
Here’s a tip: your report will be better if you know what questions you will be answering before you even do the lab. Read the lab first, making a note of where in the actual lab you will be calculating the values that correspond to the questions. Keep notes as you go along, such as what the answers to the various report questions are. It will be much easier than trying to work out everything by yourself afterwards.
Each of your reports will contain a header. In the example it looks like this:
Lab 11: Simple Harmonic Motion Julie Jones
September 9, 2016
Lab Partner: John Jackson Lab TA: Robert Schmitz
The format of yours doesn’t have to be identical to the above, but it needs to contain the same information. If you had more than one lab partner, record all their names. If you are unsure of your TA name (such as if you are attending lab on a different day) you can either ask them before you leave or check the schedule on Blackboard.
The introduction is where you describe what you did, why you did it and how you did it. This should include a brief statement of theory as it applies to that lab, a brief description of the experiment itself and some link between the two.
Here is the introduction from the example lab:
When a mass is hung from a spring Hooke’s Law tells us it will stretch by an amount inversely proportional to the spring constant, k, which is a characteristic of the spring. Furthermore, if pulled down and released, the mass (m) will oscillate at angular frequency ω2 = k/m. In this lab we hung masses from a spring to first determine the spring constant, then allowed the masses to oscillate so we could compare our measured and theoretical angular frequencies.
The first two sentences here concisely state the theory. Note that there is economy in word choice; for instance Hooke’s Law itself is not stated (see below) nor does the introduction spend time defining such things as ‘displacement’ or ‘spring’. Very often reports include unnecessary definitions or explanations that only serve to suggest that the writer was unsure of their material.
The third sentence in the example introduction includes both the experimental description and the intent of the lab. Again, less is more here. Your challenge is not just to say it, but to say it concisely.
Common mistakes made in the Introduction: – Including unnecessary equations. In rare cases they may be appropriate, but for most labs they are not. You should never include equations that are already on your data sheet (since that’s why they are on the data sheet), such as with Hooke’s Law in this example. If you do feel an equation is required, embed it in a sentence like the example did for the angular velocity equation, rather than putting it on a separate line. – Including results. That’s why there is a Results section! – Making it way too long. The vast majority of labs lend themselves to introductions of a few sentences at most. If yours is much longer than the one in the example lab, it may already be too long.
Every lab contains three or four multi-part questions at the end, clearly labeled as the questions you need to include in your report. Your result section will (only) contain the answers to these questions. Each question should get its own paragraph and all parts of the question should be answered in that paragraph.
Some of the questions will be very straightforward, simply asking for values (“What was your calculated mass?”). Often they will be more complex, requiring you to do some analysis or give an opinion (“Why do you think the image you observed is not as large as the calculated image
size?”). The better you understood the lab as you did it (and the better notes you took) the better your answers to these questions will be.
Let’s look at the results section of the example lab:
The measured value of our spring constant was 145 ± 1.85 N/m. The uncertainty in our result was due to measurement uncertainty; the meter stick was marked in millimeters, which limited our accuracy to ±1 mm.
The 0.8 kg mass had an expected angular velocity of 13.5 ± 0.2 rad/s and our measured value was 13.6 ± 0.3 rad/s. The 1.3 kg mass had an expected angular velocity of 10.6 ± 0.1 rad/s and our measured value was 10.7 ± 0.2 rad/s. The 1.7 kg mass had an expected angular velocity of 9.2 ± 0.1 rad/s and our measured value was 9.3 ± 0.2 rad/s. In all cases the expected and measured values agreed within the uncertainties.
All three masses oscillated at frequencies slightly higher than the calculated values. This may be an indication that the spring is not completely ideal. However the differences between the measured and calculated frequencies are very small compared to the values themselves therefore if the spring is not ideal the deviation is minimal.
You may wonder what the questions they were answering were. Here they are:
1. What was your measured value of the spring constant? What factors contributed to the uncertainties in your result?
2. Report the calculated and measured angular frequencies for all three masses. Are they in agreement? Comment on a possible reason for any discrepancies.
3. Do you think the spring you used in this experiment is an ideal spring? Why or why not?
As you no doubt noted when you read the example, this lab was quite successful for the students and the spring acted more or less exactly as they expected. This doesn’t necessarily mean they had an easier time writing their report, since good reports can be written about bad data. In other words, even if Julie and John had a very non-ideal spring that gave unusual angular frequency results they would still have been able to answer all the required questions and write a good report.
Let’s look at the specific questions themselves.
1. The second portion of Question 1 asks about uncertainties in their spring constant calculations. Note that their response includes some elaboration. As a result their grade will be higher than if they simply wrote something like “The only uncertainty was measurement uncertainty”. While your answers for the questions should be concise, they should at the same time demonstrate an understanding of what is being asked.
2. When comparing results, you’ll never want to say things are simply “in agreement” with each other (or the reverse). You’ll need to consider uncertainties as Julie did here. Similarly avoid subjective words such as ‘big’ or ‘small’ to describe results. Always compared your results with
theory and consider the uncertainties in such comparisons. Because of how close her values were Julie did not answer the last portion of this question about discrepancies. This is fine; sometimes questions may have optional parts like this. Most of the time though you’ll need to answer every part of every question, so be sure you understand why you are skipping a part if you choose to.
3. This question tests understanding of what ‘ideal’ means with respect to a spring, and requires you to give an opinion in your answer. This is a good example of how your report will be better if you understand the theory behind the lab. A (very) poor answer to this question would be “Yes.” or “No.”
Common mistakes made in the Results: – Not answering the questions exactly as asked. Read your responses carefully and make sure you answer each part of every question. – Not formatting it correctly. There should be exactly as many paragraphs as there are questions (which will be three or four only). – It’s too long. If you’ve written more than about a half page, you may have written too much. – Omitting units. This is a big one, and almost every student loses points for unit errors at some point during the semester. Check and double-check before handing it in. – Reporting too much or too little accuracy. Don’t round values too much or not round them at all. This mistake rarely makes it past the lab itself (your TA will catch accuracy errors on your data sheet) but in general you should report values with as many significant digits as your data. – Spelling and/or grammar errors. Every word processor has a spelling and grammar checker: use it!
Here is where you summarize your results and include some sort of closing statement about your experiences with the lab. Here’s the example conclusion:
The spring followed Hooke’s Law closely and when we used our calculated spring constant to predict oscillation angular frequencies we found they agreed within uncertainties to the measured frequencies. We concluded the spring used in this lab is very close to ideal.
Note that this conclusion doesn’t include any (numeric) results, such as the spring constant itself. This is a stylistic choice I made when writing it, and sometimes you may feel it is appropriate to restate the principle result from your experiment.
However there is a cardinal rule you never want to break with the conclusion: Never include new material in the conclusion. If it was relevant, it would have been included in the results section, so don’t feel obliged to shoehorn it in here.
A good rule of thumb for the conclusion is this: it should serve as a good summary of the results for those that don’t want to read the results. In other words you should be able to get a good idea of your experiment by reading just your introduction and conclusion and skipping the results entirely. Try this for the example lab, and see if you agree. Now try the same for your lab report. Does it make sense? If not, then you may want to make some changes.
Before you hand in your lab, read it. Many tiny errors in reports can be caught with a quick read through.
Also ask yourself whether the report effectively demonstrates what you did, how you did it and what your results were? For instance the example report corresponds to a nonexistent lab but when you read it you have a good idea as to what the lab asked them to do and in what order.
Your report should do the same. If someone who hasn’t done the lab reads your report and can’t work out what you did or what your results were then your report probably needs more work.
Lastly be sure to attach your graded data sheet to your report before you hand it in. Labs without data will not be graded until you provide the data, which means they’ll be late. Don’t let this happen to you.
Nobody is perfect, and we all make mistakes. If you lose points in your report your TA will clearly explain why and you should avoid making the same mistakes in the future.
Students that do well in lab prepare in advance, pay attention during the lab itself, follow the guidelines in this document when writing their report and learn from their mistakes. For these students their report grades typically improve as the semester continues. If you follow this advice yours should as well.