Physics 128a: Experimental Physics
Professor Jeffrey D. Richman
Broida Hall 5131, 893-8408
Rich Harding, Developmental Technician, 893-2553, firstname.lastname@example.org
Daniel Duarte, graduate teaching assistant, email@example.com
Alfredo Alexander-Katz, graduate teaching assistant, firstname.lastname@example.org
Welcome to Ph128!
The experiments in Ph 128a will give you the opportunity to observe
some fascinating aspects of light, atomic spectra, sound, and other physical
phenomena. This course will be very different from a typical course in
theoretical physics, where you attend lectures and do homework problems.
Ph128 is much more like doing actual research: you are working with real
equipment, and you and your lab partner have to make things happen. Many
students find this course to be very challenging. Don't feel bad if you
Ph 128 is hard for several reasons. To begin with, many of you have
very little experience working in a laboratory. It's quite different from
reading a textbook! Here is the basic method:
Realize that you are totally confused about everything.
Formulate a set of specific questions.
Formulate a strategy for answering at least one of the questions.
Carry out this strategy.
Go back to 1.
Students who have the most trouble are usually the ones of have done
little or no preparation before coming to the lab. Without preparation,
you have a hard time even formulating specific questions (Step 2). In
most of the experiments, your time in the lab must be used efficiently,
so planning your strategy in advance is extremely important!
Second, there is a lot of theoretical physics involved that you have
not learned in your classes. Before you can understand each experiment,
you will need to do some research on its theoretical aspects. Here are
just a few examples:
If you add a neutron to the nucleus of the hydrogen atom (a single proton),
what effect will this have on the energy levels of the atom? Will it have
any effect at all?
How does a gas laser work? What are the properties of a laser beam?
What determines the speed of sound is a gas? What molecular properties
How is the flow rate of a gas affected by the dimensions of the tube it
is flowing through?
How are diffraction patterns and Fourier transforms related?
What is a hologram?
You will need to do substantial reading on your own just to understand
the theoretical issues underlying your experiments. It is crucial that
you move quickly in each experiment to do this.
To help you do this research, we have a small library of books that
you may check out. In addition, most of the labs have documentation that provide theoretical
background. If you check out a book, you must return it by your next lab period.
Of course, going to the library is also a great idea. Far too few students
make use of that powerful resource.
A third reason this course is difficult is that you will be presented
with a substantial amount of equipment with which you may have very little
familiarity. If you are struggling to figure out how it works, you can
Fiddling around is fine, as long as you are careful not to destroy anything.
If a piece of equipment is not working, either in the state you found it
or because of something you have done, you should report it immediately
so that we can fix or replace it. You will not get in trouble if you break
something, but you will be in trouble if you break something and don?t
tell us. Although it may be quite difficult at first, you will gain
a lot of self-confidence if you learn to open up a manual, find the relevant
section, and figure out what?s going on. While some of the pieces of equipment
can be regarded as "black boxes" without affecting your results, in other
cases, you will not be able to successfully perform the experiment unless
you really understand how the equipment works. This task may involve even
more physics that you don?t already know! In addition, you may also need
to learn some of the eccentricities of the equipment, especially if you
want to get the best precision on your measurement.
fiddle around with it,
read the manuals in addition to fiddling around,
ask for help.
The fourth reason this course is challenging is simply that it is always
hard to get the right answer. I discuss this point in more detail below,
under "Goals of the Course."
You will choose four experiments, spending two weeks on each
one. The list of possible experiments for this quarter is:
Hydrogen/deuterium isotope shift
Properties of laser light
Scattering of light by polystyrene crystals
You will also do a small project in the machine shop to gain some experience
with machining techniques. For your reference, the list of experiments
for Ph 128b is:
Nuclear magnetic resonance
X-ray diffraction crystallography
Quantum Hall effect
Some of the experiments are challenging, and I urge you to do as much
preparation as possible before starting each one. The experiments are also
quite rewarding, however, and I hope that they make some difficult physics
more tangible and immediate to you.
There are important safety issues in some experiments. This is particularly
important in Ph 128b, where we use an X-ray machine and radioactive sources,
but there are also safety issues in some of the Ph 128a experiments.
I require that you start each experiment by doing an assessment of the
safety issues. Please work like a professional and be actively involved
in your own safety:
Look for safety-related information in the lab manual.
Look for safety-related information in the manuals for the equipment.
Ask me, the T.A.?s, or Rich Harding about anything that concerns you.
Record important safety-related information in your logbook.
Usually, it doesn?t take long to inform yourself about safety issues,
and it is well worth the trouble. Some typical examples of safety hazards
If any type of accident occurs, you must report it as soon as possible
to the instructor, Rich Harding, or one of the T.A.s. If for some reason,
there is an emergency and no one is around, you can go to the Physics Department
Office on the third floor and ask someone to call 9-911.
Intense light sources: lasers or gas discharge tubes. Never look directly
into a laser beam. In addition, be careful not to look into a mirror or
other polished surface that may reflect laser light directly into your
eye. When working with lasers, it is always a good idea to keep the level
of your eyes substantially above the level of the laser beam. Avoid looking
directly at gas discharge tubes. In some experiments, we have provided
eye goggles. If you would like a pair but they aren?t around for some reason,
feel free to ask us and we will get some.
Electrical hazards (high voltage);
X-ray machines, radioactive sources (Ph 128b)
THE MOST IMPORTANT RULE OF THIS CLASS, WHICH MUST NOT BE BROKEN IS:
You may work on an experiment after class hours,
but there must always be at least two students together in the room.
The requirements are:
Do four experiments, and keep a good logbook record of each one. The logbooks
should not just be spiral notebooks. Please keep two separate logbooks
to facilitate grading; the T.A.s will grade one while you are using the
other for your next experiment.
Carry out a small project in the machine shop. You will also receive training
in safe machine shop practices.
Give one talk; this will be after the second experiment, and it can be
on either of the first two experiments. You will give this talk jointly
with your lab partner using transparencies and an overhead projector. We
will provide blank write-on transparencies, but you should get your own
pens. The best ones are Staedtler Lumocolor Fine-point permanent pens.
You may also use a computer to generate your talk. You will then need to
use a different kind of transparencies.
Write one abstract. The abstract is about one paragraph long and will be
due after the third experiment. It can be on either of the experiments
that were not the subject of your talk.
Write one full scientific research paper. The paper will be due after you
complete all four experiments, but it may not be on the same experiment
as the one your give your talk on. It may be on the one you have written
your abstract for, but in general you will need to rewrite your abstract.
To determine your final course grades, I will use the following weighting:
Experiments + logbooks: 75%
Abstract and Paper: 17%
Goals of the Class
There are several different goals for this class.
Learn to work in a laboratory. We are trying to train you not just in physics
knowledge, but also in the methods of working scientists in almost any
Be tough-minded and skeptical.
Develop an approach that is systematic, methodical, careful, and organized.
Prepare ahead of time and try to anticipate the issues that you will need
to address. This is extremely helpful in using your time in the lab efficiently.
In many real-world experiments, you have limited access to a shared piece
of equipment, such as an expensive telescope, and preparing yourself in
advance gives you a much better chance to complete your investigation within
the allotted time.
Understand the sources of experimental uncertainty and the limitations
of your apparatus. Effort spent on understanding how your equipment works
is almost always rewarded with more reliable results.
Learn how to record results and how to describe your setup and procedures
so that the conditions under which your results were obtained are completely
Learn proper methods of data analysis.
Learn how to draw conclusions that are specific, meaningful, and justified.
Learn some modern physics. In your classical mechanics and electromagnetism
classes, you are learning physics that was developed about 100 years ago;
in quantum mechanics, you are learning physics from the 1920s and 1930s.
In this class, you will learn some physics that is based on much more recent
work. This will be challenging, since you may not have encountered much
of this physics in your theoretical classes.
Learn skills for giving talks and writing papers. These skill have a very
wide applicability. They are extremely important in any scientific field
and in many non-scientific jobs as well.
Learn to obtain information from many sources, not just a single textbook.
||Sept 28, 30 (29, Oct 1)
||Oct 5, 7 (6, 8)
||Oct 12, 14 (13, 15)
||Oct 19, 21 (20, 22)
||Oct 26, 28 (27, 29)
||Nov 2, 4 (3, 5)
||Expt 3; talks on Nov 4, 5
||Nov 9, 11 (10, 12)
||Nov 16, 18 (17, 19)
||Expt 4; abstract due Nov 18,
||Nov 23, 25 (24, 26x)
||Expt 4 (x=Nov 26 is holiday)
||Nov 30, Dec 2 (1, 3)
||Finals week: paper due Dec
Some important dates:
For the M, W section, the talks will be on Weds, Nov 4
For the T, Th section, the talks will be on Thurs, Nov 5
For the T, Th section, there is one holiday, Thursday, Nov 26. We will
try to work around this problem as best we can, for example, by having
you come in on Friday of the previous week or during the following week.
The papers will be due on Thurs, Dec 10. Note, however, that since you
can write the paper on any experiment expect the one that you give your
talk on, you could in principle hand it in earlier!
J.R. at Fermilab on Oct 22, 23; at SLAC Oct 26-29; at Berkeley Nov 11,
Grading of Logbooks
The logbooks will be due one week after you complete the experiment.
Thus, for the M, W section, the logbooks will be due on the W following
the two week period for the experiment; for the T, Th section, they will
be due on the Th following the two week period for the experiment. The
logbooks will graded on a scale from 1 to 20. Late logbooks will be accepted,
but with 2 points deducted for each day late. If special circumstances
arise, please discuss them with me as soon as possible.
Each group will give a 15 minute talk, which will be followed by 5 to
10 minutes of questions. The talk should contain
All together, you should have 8-12 slides. Please label all plots and give
the units for all quantities. The talks will be timed with a hard cutoff,
so you should practice your talk to
A title slide, with title, authors, and main goals of the experiment.
2-4 of slides on theoretical background.
2-4 slides on the method.
2-4 slides on the results and conclusions.
make sure that it fits into 15 minutes. Sometimes, extra or "backup"
slides are useful during the question period. The talk should be divided
between the two lab partners, with roughly equal time for each student.
The paper should contain the following sections:
Methods and Procedures
Interpretation and Discussion
The abstract is meant to be a stand-alone description of the work-it
should succinctly state what was done and what the results were. It should
not refer to any other section of the paper, and it should not go into
the theory, except perhaps very briefly. An abstract should not read like
an introduction, which contains background information and is not a summary
of the results. You should include the numerical values of important measurements,
with their uncertainties. A person opening up the journal to your article
will read the abstract first. If they are busy, this may be all that they
will ever read!
You should write a section on the theory behind your experiment. Do
not mix your results or interpretation into this section, which should
be 2-4 pages. (If you want to write more, it?s fine with me.)
Experimental Methods and Procedures
Include at least one clear diagram of the experimental setup. Be sure
to describe your experimental methods in detail. The length of this section
will depend on the experiment that you did, but as a guideline, it should
be between 3 to 5 pages. Detailed figures add a lot to the clarity of such
Tables are great for summarizing results. In some cases, graphs are
preferable to tables, since they make it much easier to see relationships
in the data. In fact, a lot of students miss important observations because
they don?t bother to graph their data. Be sure to include a discussion
of how you estimated your experimental uncertainties in the raw data and
how you propagated these uncertainties into your final results.
Discussion and Interpretation
I prefer to have the interpretation of the results in a separate section
from the results themselves, since it explicitly separates what you measured
from your interpretation. This rule may not apply to all situations, so
if there is a strong reason to combine this section with that on Results,
you can do that.
If there are important theoretical or experimental results that you
wish to use in your paper, they should be referenced. In the body of the
text, put a reference number, and
list the references in numerical order in this section.