In these experiments, you are dealing
with extremely small "signals" which would not be directly measurable; therefore, clever techniques are needed
in order to amplify the effects of "small perturbations". Careful
consideration of technique and uncertainty will enhance your experience.
We'll all watch a brief, classic movie on this topic. During the viewing, make
detailed notes in your lab notebook. I will collect and examine these
notes.
After I return your (graded) notebooks, with
comments, you will be given a more detailed article from the American
Journal of Physics [D. H. Frisch, J. H.
Smith, Am. J. Phys., 31,
342 (1963)]. After a careful reading, you'll be further prepared to begin doing
science in this course. Towards this end, everyone
will write a summary of the arguments used in this paper. This summary should
provide an outline of how the authors use scientific method and, in particular,
how they deal with possible systematic and random errors. You'll want to be
brief, but thorough!
The acquisition and graphing software packages that
you may have used in your Introductory Physics coursework, "Data
Studio" and "Graphical Analysis", have the advantage of
simplicity (e.g., Graphical Analysis offers clear visual reinforcement of the
iterative nature of the adjustment of fitting parameters in order to achieve a
"best fit"). However, professional work requires that you have much
greater flexibility and control over the data acquisition process, and that
when analyzing data you be able to report statistical uncertainties for each of
your fitting parameters (something that last year's software is not set up to
do). Thus, we introduce you to LabVIEW (the industry standard for data
acquisition and instrumentation control) and KaleidaGraph (which requires the
use of a scripting language for fits involving complicated functional forms,
but which offers the more complete statistical reporting we now require).
Outside of the scheduled meeting time, you should teach yourself
LabVIEW, and should also work through the "Guided Tour of KaleidaGraph" (Chapter 2 of the KaleidaGraph manuals lying
about)
Do not put this off.
During this (three week) round, you may do one or more of the following labs
(or propose your own alternative, as described at the end of this page). Last year,
some students made the mistake of doing no lab work outside of the scheduled
meeting time. Certainly, everyone realized that such behavior would be foolish
for non-laboratory coursework in physics, but because the introductory-level
labs had served a very limited role in the 100-level courses, some remnant of
that mindset must have been preserved. Here, the lab constitutes 25% of your
course grade, so I'm hoping that this is something you'll enjoy putting
significant effort into.
Luckily, you have the benefit of learning from the mistakes of some of last
year's students: make every week count!! Only those who try to actually complete
their work during
the first week are likely to develop a significant, satisfying body of work
over the course of the round. [Once you do complete a lab, the goal is to extend that work in the subsequent weeks.]
Although these experiments do demonstrate some concepts that may be new to
you, they invariably rely upon principles which you have already learned. Use
your introductory text!! You are to use the sorts of physics that you already
know in order to think through how your equipment is intended to operate, to plan your
measurements, and to consider what can be learned. Importantly, the entire process
should be documented in your lab notebook.
[On the use of references: Please provide a clear citation in your notebook,
guiding your reader to the location in a text where you found useful
information. Moreover, please note that it is far from sufficient to merely provide a citation: in your notebook, you must work
through the key arguments and derivations that you have extracted from your
references. Finally, a failure to provide proper citation constitutes plagarism.]
You can't easily measure ultra-small currents,
right? So if you have, say, thirty electrons passing by a detector each minute
... is that a measurable current? For
this lab, you'll want to figure out the operation of a Geiger tube. This labcan
be (if you like) extended in any number of
ways (Radioactive Dating, Range of Alpha Particles, etc.). There are many related
articles available in the literature [e.g.,
P. J. Ouseph, Andrew Mostovych, Am. J. Phys. 46, 742 (1978)], but we do supply a
Phys 105-style write-up, should you desire one.
Want to clearly see that the experimental relationship between energy and momentum requires
relativity?
This lab also uses a Geiger counter, but here it is
incorporated into something like the mass spectrometers you encountered in your
earlier coursework. You'll need to sort out some of the set-up and the
experiment on your own (using what
you learned in Phys 106).
[You should also go to the library and do a citation
search on Jack G. Couch, Terry K. Dorries, Am.
J. Phys. 50, 917 (1982).
Although this is not quite your experiment, it is close enough to make for good
reading.]
You can't "see" an electron, right? Well,
no - not directly. On the other hand, you may be able to see the
"trajectory" of an electron.
Have you ever heard of a cloud chamber? The idea is
to create an environment that is supersaturated with vapor, so that particles
passing through leave "contrails" of the sort airplanes sometimes
leave in the sky. You should read and think carefully about what it means and
takes to create supersaturated conditions; without sufficient understanding,
your chances of success are significantly diminished. Many designs have been
suggested for the construction of cloud chambers. Can you get one to work? It's up to you to learn what's needed to make it
happen!
By studying the effect of fields (e.g., a magnetic
field) upon the "tracks", one can begin to learn about the nature of
the particles that create these tracks.
If you'd prefer to "cut to the chase", we
already have photos of particle tracks taken under well-documented conditions
from a research-grade (bubble) chamber. Careful analysis is aided by several
experimental tools.
Suggested Journal Reading includes
(but is not limited to):
1) American Journal of Physics
2) Review of Scientific Instruments
Again, the laboratory portion of this course is designed to offer flexibility:
those interested in finding their own
experiments to do or apparatus to build will find some nicely accessible
articles in these journals.