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Physics Lab

  1. Sep 23, 2009 #1
    Basically I am taking the lab concurrently with the class, unfortunately we learn how to do the lab a few weeks after we do it so its becoming quite depressing. I could probably slide out of it with a B or C and get absolutely nothing out of it. I should have waited to take it butI didnt realize it would be such a problem. Is it better to drop it and take it next semester when I can actually do it or just get a C this semester? They both look like bad but which is worse? At this point its simply demoralizing. I mean it seems pretty ridiculous to get a W for a lab course but a C is not much better. Any advice would be appreciated.
     
  2. jcsd
  3. Sep 23, 2009 #2
    Umm I am from Britain and am studying Physics at university over here, so anthing I say may not be relevant.

    However why do you need to know the stuff in the class? Here we do not have lectures before any laboratory sessions. We merely look at the experiment we are going to do, then go and find out as much about it as possible (this includes leaning the theory behind it if necessary, and also reading any papers which are of similar experiments), we then plan what we are going to do and do it. Obviously you have to have some sort of electronics knowledge and also know about errors analysis. However if you are unsure of this you can just ask a lab demonstator. Infact this is actively encourages as it enhances understanding, although the ability of some of the PhD kiddies is dubious.

    If you did this would you not be able to get the most out of your lab course? If the structure is very different to what I have described above, can you not just go to the module convener and speak to them. They may be willing to give you a copy of the lecture notes in advance of your lab session, they may also be able to move your lab timetable around to be accommodating to the other module. Sorry if this is not much help.
     
  4. Sep 23, 2009 #3

    Choppy

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    This is a chicken & egg issue. On one hand, it's nice to do the lab first, get the practical experience on a particular topic and then have that as a reference for the lectures. On the other hand it's nice to have the background material covered before you start working with a topic on a practical basis.

    Speaking as a person who TA'ed for several years, most of the difficulties students have in the lab aren't so much the specific physics topics under investigation. Rather, they have to do with the experimental process: calculating uncertainties, linearizing data, statistical analysis, etc. This stuff is usually covered in the laboratory manual and it is sometimes left to the student to learn it independently.

    The biggest trick to doing well in labs is to READ AHEAD. When you show up for the lab, you ideally should have read over all aspects of the lab, decided what data you need to take, how you are going to record it an plot it, what your uncertainties are expected to be, and reviewed the relevant chapters in your textbook. Some keen students will already have tables prepared and formulas worked out. If there's something you don't understand, you should attend your professor's or TA's office hours for additional help.
     
  5. Sep 23, 2009 #4
    Hey Choppy,

    What is the standard operating procedure for determining the uncertainty in measurements? For example, if I'm using a balance that measures to 0.0001 g, how do I determine the uncertainty? Should it be provided for that specific instrument by the professor or TA? Or do I just assume that it's 0.00001 +/- ?

    My first (Chem) lab never mentioned uncertainty or statistical analysis at all. The second part of that sequence made a couple of passing references to it at the start, but doesn't seem to be making any reference to it going forward.
     
  6. Sep 23, 2009 #5

    Choppy

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    The uncertainty in a measurement depends on the resolution of the device you're using to make the measurement, the nature of the object/phenomena being measured, and your confidence as an observer.

    What you're talking about in the example above is essentially the resolution of the balance. If that happens to be the limiting factor (ie the factor with the largest uncertainty) in the measurement then you can take that as your uncertainty. However, what if I wanted to use that balance to determine the mass of say, a human being? Continuous biological processes such as respiration, sweating, vibrations from a beating heart, etc. might make it difficult to determine that mass to within 0.1 micrograms. If I record the fluctuating readout over time, I would likely find a distribution of values about some mean. Assuming that these results have a normal distribution I could take the standard deviation, or perhaps 2 standard deviations, as my uncertainty. If this turns out to be 20 micrograms, the increased resolution of my device is no longer the limiting factor.

    This is the kind of thing that should be outlined in your lab manual. If it's not, get your TA or professor to explain it in detail.
     
  7. Sep 24, 2009 #6
    It's absolutely not in the manual; thank you for the explanation. It's a bit confusing, but rather interesting. Amusingly enough, I'd just so happened to watch the first of Dr. Lewin's MIT OpenCourseware lectures last night where he was discussing uncertainty in measurement.
     
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