FYS 274 Lab: Getting Started
FYS 274 – Physics in the Twentieth Century
Why do we have lab, anyway? You might think it’s just to illustrate class material. That’s a pretty good reason, but not very related to the role laboratories play in the real world. We are more interested in showing you how laboratory observations lead to a description of nature, and in letting you experience how the inherent limitations of laboratory work lead to uncertainty in that description. If you stay focused on these goals as you work through these labs, you are likely to begin wondering how the supposedly “exact” sciences could be so heavily based on laboratory work! Then we will have succeeded, because you will be more skeptical of science in general and more appreciative of the accomplishments of history’s great experimentalists.
We try to keep the focus as much as possible on the lab itself, and less so on the “publication” aspect of professional (especially academic) science. We emphasize the initial recording of experimental data in a laboratory notebook, and the preliminary analysis of that data to determine experimental results. We ask you to develop a style of record-keeping that is practiced in real research laboratories, where it may be as important to establish the chronology of events as it is to describe those events accurately. You may sometimes feel as if we are imposing an arbitrary set of picky rules, but if you make this note taking style a habit, it will serve you well, even if you don’t become a professional scientist.
To keep you aware of the limits of laboratory observation, we ask you to calculate the “uncertainty” in your experimental results. We don’t call it “error analysis”, because that implies you did something wrong. You shouldn’t make errors, but you should be uncertain! We intend that uncertainty analysis be a significant but minor part of your work for each lab. In the past, students have done much more than we now require for this part of the lab, so don’t listen to what they tell you. Just follow the instructions on the pages that follow! If you aren’t sure how they apply in a given situation, ask us to make it clear before you start calculating. Briefly, we ask you
1) to estimate the “measurement uncertainty” once only for each variable that you measure, justifying your estimate
2) to do a “partial uncertainty analysis” for a single data set
3) to use the “standard deviation technique” when instructed to do so. We also require that you do all your analysis in Excel. The physics 108 Excel Tutorial describes this spreadsheet program. There is a link to this tutorial from the physics 108 webpage.
We intend the lab to be interactive. We tried to write this manual in a way that keeps you thinking about what you’re doing, but we also want you to consult freely with lab instructors, the student assistant, and other students. The questions in the lab manual are meant to stimulate such conversation. In some cases there is no single answer, or the answer is beyond the scope of class material. We ask that you answer the questions as you come to them in lab, so it will be easier for you to discuss them with us.
The Lab Notebook
The most important thing to know is that it’s your notebook. You are writing notes in your own words, for you to read and understand later. It’s not a report that you’re writing for the instructor. It’s more like a diary. Each experiment should begin with a title, purpose and your partner’s name. The notebook is supposed to be an accurate record of what happened when you did the lab. That means you write down what you do when you are doing it, not the night before or a few days later. It must be sufficiently detailed to “stand alone”; that is, you or the grader should be able to understand what happened without also having to look at the lab manual. Diagrams are especially helpful in accomplishing this. The notebook is supposed to indicate the order in which things happened. That means it’s strictly chronological. Never leave blank spaces with the idea of coming back later to fill them in. It’s supposed to indicate everything that happened.
Thus you write only in the notebook, never on “scrap paper”. It also means that if you make a mistake, you don’t erase, obliterate, use white-out, or tear out the page – just draw a single line through the mistake or a single cross through the page or section of page that should be ignored. You should still be able to read the supposedly mistaken information – it can happen that the mistake actually tells you something valuable that you’ll want to know later. The notebook is supposed to indicate when things happened, so each page must be dated. Because your notes are strictly chronological, you often need to refer back to something written earlier. That means the pages must be numbered like the pages of a book–if your first experiment ends on page 17, the second begins on page 18, and the last page in the book is page 160 or so. Sometimes you need to refer forward. If you break off an analysis on page 30 and pick it up again five pages later, label the break off point with something like “continued on page 35″ (O.K., in this case you are allowed to write something out of strict chronological order!), and on page 35 write “continued from page 30″. Your conclusion should always restate the purpose of the lab, the final results and whether they agree with each other and/or an accepted value, greatest sources of uncertainty, and suggestions for improvement. Finally, the notebook is supposed to be a permanent record, so use pen only, and never insert loose papers. Use the tape provided in lab to immediately fasten individual computer plots or printouts to separate notebook pages.
There are penalties for late labs that are noted on the Laboratory Grading Guidelines page. A lab turned in less than 19 hours late will receive a 2-point penalty. If the lab is more than 19 hours late it will receive a 5-point penalty for that day and another 5 points for each day beyond the first day. The maximum penalty for a late lab is 20 points. Labs turned in beyond 4 days late will receive a maximum grade of 16/36, however must still be completed in full (in-lab and take home analysis must be completed). Because labs are an important part of an introductory course and there are only 5 lab experiments, you must complete all 5 labs to pass the course!