Sunday, June 22, 2008

Lab classes

I actually started writing this back in April of 2007 ... see bottom of article for references to the prompting articles and some more recent ones. That put it on my list of things to do looking back at my first year of blogging. Also, if you have not already done so, take a look at the previous article and reply to the poll question about recording lab data.

I think I have a pretty clear idea of the main objectives and how to achieve them in my calc-based physics lectures, but I will resist the temptation to outline them here. However, my feeling for the main objectives of the corresponding first year lab classes is another matter. OK, I think I know what the important ones are, but I can't identify one or two that should be emphasized above all others and it seems impossible to get the students to make all of them a priority. Is it because they have their own idea of what the lab goals are? Do those skills, subtle as they sometimes are, appear too mundane? Is it the challenge of critical thinking? Is it because they look at each lab as something like a science fair project back in elementary school? Or are my priorities wrong?

Side thought:
One way to find out what the students think is to simply ask them that question this fall. (Might even be good to ask them what they think the purpose of the lecture class is!) But right now I am using this question along with my own musings on the subject in the hope it will clarify my view of the lab.

The subject here is the first year physics lab (or chemistry lab), not one of the advanced labs taken by a physics, engineering, or chemistry major. However, I would love to get your short list of things that students don't know when they take a junior-level physics or engineering lab if you have experience teaching one of these. I learned one of those details from a lab TA at a nearby engineering college and have incorporated it into my assessment at several points.

OBJECTIVES:

Technical writing will be taken up in a separate article.

So which one or two of the following items do you think is most important, or is there something I left off of my list? Feel free to add any other thoughts you might have.

1. Making the measurements correctly.
I am always surprised how many students don't want to use all of the information available on a ruler yet blame the instrument for their own lack of care. (I'll bet real money that this is why they prefer digital devices despite the fact that all of the same digits are on the analog device.) I think one of the most important objectives is to understand the importance of getting the most out of whatever tools are available.

2. Recording the measurements.
Part of this is the simple skill of writing down the value (in ink) that was measured, but the other part is estimating the uncertainty and using the uncertainty and significant figures to tell someone else how carefully you think the measurement was done. High on the list has to be the basic step of reporting a measured value in a way that clearly indicates its reliability (and its units, of course). Is this something you specifically test on lab exams?

3. Following directions.
Some labs have a rather detailed procedure that needs to be executed step by step if the equipment is to work properly. I'd say that half of the procedural questions I get in the lab are answered in the lab manual, indicating that it has not been read and/or read with comprehension.

4. Design your own experiment.
Our labs are not as "cook book" as those in first semester chemistry, but they leave no room for student creativity -- primarily to avoid major student blunders that would make the work impossible to grade and keep the student from learning anything about the phenomenon being studied. Do any of you do this, or do it as part of a practical lab exam (e.g. design a set of circuit experiments to figure out what is inside this black box)?

5. Critical thinking with uncertainties.
A related, and exceptionally challenging problem, is getting across the idea of what criteria must be met for an experiment to "agree" with a prediction or a known value, or to establish that some effect (e.g friction) is or is not present at a significant level. I think this last one is particularly difficult because so many first-semester lab experiments don't work all that well in the hands of amateurs, so I push it mainly in the second semester.

6. Learn from mistakes.
Probably the most irritating thing to me are the students who make the same kinds of mistakes all year, often as a result of failing to prepare for lab or simply being in a hurry to get out and "get away with" doing the least amount of work possible. Do you ramp up the grading penalties as the semester goes on?

7. Hands on experience with the phenomenon.
Sometimes we want them to simply experience the phenomenon, as a way of reinforcing or illustrating what goes on in lecture. They really like these labs when they are tightly linked to lecture in a "studio physics" style of learning, much more so than a corresponding demonstration in lecture. Should there be more emphasis on this, or would that hurt their preparation for advanced labs in engineering?

8. Respect the limitations of digital meters.
Students (including those in my generation, who did not grow up with calculators) have a near-religious belief in the perfection of any number generated by a digital device. They do not know their calculators use BCD arithmetic with guard digits to hide their inherent flaws from view in trivial calculations. They do not know that calculations done by their computer running a program written in C++ (or any other language) use a different system with different flaws. Thus they think that every digit displayed by a multimeter is 100% reliable, like the mark on a ruler. They don't even suspect that those numbers are actually raw data from an analog physics experiment, so they are stunned when they don't round to the value displayed when you select a different range on the meter. This is one thing that I plan to explore in more detail during our initial lab in physics 2 this year.


***


Background articles from out in the blog world, mostly circa the spring of 2007 ...

A few of the problems I suspect originate with student perceptions of our labs as an extension of ones done in elementary school or high school could benefit from the kinds of reforms Chad Orzel proposed for the physics-major curriculum, which were centered on the introductory physics class I teach. I also like Chad's succinct rant and more detailed critique of remarks from some silly philosopher who thought labs are not real classes. Not only do I agree with some commenters that labs are more work than "real courses", I insist on teaching a certain lab to be sure students are forced learn certain skills. And I am a theorist, not an experimentalist, thus proving that a theorist is not a philosopher.

I suppose the reason that the Playground Philosopher doesn't like labs is tied into preferring thought to action. But would you prefer to drive over a bridge designed by an engineer who used pure thought to come up with the strength of the steel being used, or one who used a measured value and had done enough measurements to have a gut understanding that there are uncertainties in that measure value, no matter what the data book says?

Other critiques of that philosophical position were written by Dr. Stemwedel Labs and learning science and in Chad Orzel' third article about Labs and Learning. A related thought also appears in Chad's article listing "to plan and carry out a simple experiment" as number 1 on the list of skills every physicist should have.

There were articles by Female Science Professor on using basic methods rather than automation in the lab as well as a related one by Professor Orzel on whether to automate data taking. I find that automation (e.g. some of the PASCO sensor systems) hides what has gone on in the measurement but makes it easy to do a many-part experiment in a practical time frame.

Chad Orzel wrote about reforming intro labs in a comment responding to one of the earlier parts of a 5 series on altering the approach in the intro lab.

I'll also link to a March 2007 by Female Science Professor about 100% men in labs. It's not specifically germane to this particular topic, but I have noticed that it is really important to watch who gets paired up with a female student in the lab. There are way too many guys who lack any clue about what they are doing but possess massive amounts of bluff that convinces their lab partner they know what they are doing. Young men are more immune to this than young women, although anyone who lacks confidence is likely to fall for it. Ideally, I put the clueless guys together and let them bluff each other.

Link forward added:
I wrote more about the subject in this last paragraph in an article published in July 2008.

3 comments:

Astroprof said...

Hmm. You raise good questions. I have been thinking of revamping our intro physics labs for a while. But, part of that requires knowing what we want the students to get from the labs. I am thinking that for a beginning class, getting hands on experience with phenomena to reinforce the lecture is the most important, going hand-in-hand with following directions. I would love for them to make measurements and record them properly and to handle uncertainties correctly. I try to get that across to them, but I put a lot of that off until later.

Doctor Pion said...

That is the problem, I think: wanting too much from the lab, but not having an obvious criteria to narrow the focus so the students can try to perfect a few skills each semester.

Doctor Pion said...

Not actually about labs, but nanoscale views wrote a good article about what makes an experiment 'good'. Some of those features apply to a good choice for a lab and provide a different perspective on the learning objectives for a lab. Ideally, we want to get our students started down the path where they can judge if an experiment is 'good' or not.