Course Description
Physics U600 –
Advanced Physics Lab-1 – Summer 2009
Don Heiman,
Northeastern University, 5/22/09
Introduction
Experiments in the
Advanced Physics Lab-1 course are substantially different from those in
introductory physics laboratory courses -- they go beyond the simple
demonstration of basic physical principles. More advanced physics concepts will
be explored by in-depth analysis of the data. Check out Feynman’s
1937 lab report.
Among the main
goals of the course are:
(1)
Become intimately
familiar with each apparatus in order to collect precise as well as accurate
data;
(2)
Determine the uncertainties
in the both measured and final values; and
(3)
Look for
deviations from initial expectations and basic theory in these "real
life" systems. Historically, these unexpected results have led many
researchers to new discoveries, even Noble awards.
Although many of the experiments are given as cookbook recipes
to be followed item-by-item, you are expected to continually ask yourself
questions about your observations. Even chefs
experiment with new ingredients and techniques while periodically tasting the
results. In a similar vein, a successful experimental scientist continually
asks, "why is that happening" or "what if I do this." All the while
the scientist periodically examines the results. A mentor of mine at MIT,
Dr. Si Foner the inventor of the modern magnetometer,
cautioned against taking too many sequential steps. Instead, his experience
taught him to: (i)
take a few steps; (ii) look (plot) at
what is happening; then (iii)
determine what to do in the next few steps. Thus, it is essential to plot
data as it is taken so that strategic decisions can be made quickly and
errors discovered. Incidentally, behavioral scientists have found evidence that
people learn better by not seeing answers clearly at first, rather it is often
better to see things not so clearly at first so that the brain gropes for
preliminary answers along the way. This groping leads to stronger neural
connections in the brain. Be prepared to be frustrated at various times during
these experiments, as this is closer to reality and increases your
problem-solving ability.
Experiments
Six of the
following experiments will be performed during the semester. Experiments
will be performed by groups of 2 students. Since there is not enough
apparatus to accommodate all groups doing the same experiment, different
experiments will be conducted simultaneously.
The Driven Harmonic Oscillator -- A horizontal sliding mass and
spring system is mechanically driven by a reciprocating motor.
Measurements of the amplitude versus frequency lead to determination of the
resonance frequency and damping.
Coupled Electrical Oscillators -- This experiment explores the
properties of a single LRC oscillator circuit and studies what happens when two
such oscillators are coupled and allowed to exchange energy.
Acoustics and Fourier
Transform -- A
variety of sound waves will be recorded as a function of time in order to
mathematically obtain their Fourier spectra. The harmonic components of
various sounds and musical instruments will be investigated.
Nanomagnetism -- Ferromagnetic
particles smaller than ~100 nm are no longer able to sustain their
ferromagnetic moment at room temperature due to thermal fluctuations. Rather,
they become superparamagnetic at low
temperature. The superparmagnetic
properties of magnetic nanoparticles will be measured as a function of
temperature in a SQUID magnetometer.
Hall
Effect -- This
Lab demonstrates the Hall effect in a semiconductor
and uses it to measure the carrier type (electrons or holes) and carrier
concentration in a doped semiconductor wafer.
The carrier mobility is determined from the measured resistivity.
Fuel
Cell -- The objective of this
experiment is to study the efficiencies of converting energy between light,
chemical and electrical. The apparatus uses: (1) a photovoltaic (PV) solar cell
to convert light energy into electrical energy; (2) an electrolyzer
to convert electrical energy into chemical energy by splitting water into
hydrogen and oxygen; and (3) a hydrogen fuel cell to convert chemical energy
into electrical energy.
Speed of Light -- This experiment introduces optical
communication apparatus. A high frequency voltage pulser
and diode laser generate nanosecond light pulses. Using a high bandwidth
photodiode and 500 MHz storage scope, the time of flight of individual light
pulses will be measured as a function of distance. Several different
materials will be inserted into the beam path to determine the speed of light
in these media, including water and glass optical fibers.
Ruby
Spectroscopy -- The energy levels of chromium in a ruby crystal are
investigated using the technique of absorption
and photoluminescence (PL) spectroscopy.
First, the spectrum of light absorption of the Cr ions will be measured
with a spectrometer. Second, a laser is used to excite the Cr ions and the
emitted fluorescence spectrum is analyzed.
Finally, the excitation laser is pulsed and the fluorescence lifetime of
the Cr ions is determined.
Faraday Rotation -- An optical system will be constructed
which is capable of measuring the rotation of optical polarization to a
sensitivity of 10 microradians (1/1000 degree).
Linearly polarized light passing through a sample material experiences rotation
of the polarization vector when a magnetic field is applied. The rotation
angle is proportional to the magnetic field and the constant of proportionality
is the Verdet constant. This constant will be measured for glass and
water.
Lab Notebook
A new bound notebook is
required. Thin spiral bound or research notebooks are acceptable.
All raw data
is to be recorded in the notebook or file as it is taken. Set up tables with appropriate columns.
It is usually a good idea to leave room for additional columns on the right for
analyzed data. You may find that after taking a few data points the table
is insufficient. In that case, simply begin a new table with a better set
of columns and insert the previous data -- never erase seemingly unwanted data,
as in hindsight it may be useful.
Plot appropriate data as it is taken. These initial plots can be very crude.
This allows you to see where additional data points are needed and which data
points need to be retaken.
Lab Reports
Each student must submit a separate printed Lab Report. Include
diagrams of the apparatus, tables and appropriate plots. The following
“publication” format below is required:
Title
Author, Course, Date
Abstract
Brief summary, 1 short
paragraph, < 8 sentences
State: (1) what you did and (2) what you found
Include final values with uncertainties and expected
values
I. Introduction (1 or 2 paragraphs)
·
briefly state the
physics underlying the experiment (what is being tested)
II. Apparatus
·
diagrams or
sketches of important apparatus (label items and describe in the text)
·
list equipment
components (model numbers and brief specifications)
III.
Procedures, Results, and Conclusions
Because
there are several parts of each experiment, it is often better to discuss the
procedures, results and conclusions of each part before going on to the next
part. For each part of the experiment include the following.
·
describe the
experimental procedures (in your own words)
·
discuss
calibrations, etc., if required
·
plots showing
relevant results (label each figure, e.g. Fig. 3, with caption)
-- curve fit the data to theory whenever possible
-- include only one example of many repeated measurements unless noteworthy
-- put error bars on all data points; if there are 5 or more points use one
typical error bar
·
report final values,
uncertainties, and units
in a table
·
discuss the
comparison of theory and experiment (are they within the uncertainties)
·
what could be
done better if you had more time or equipment
(See the example
Lab Report on Faraday
Rotation. Note that this report is much more
extensive than required for this class.)