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Tracking
through =
modern
physics =
laboratory
Mark F. Masters, Timothy T. Grove, and David P. Maloney
Supported by DUE #0127078 from the National Science
Foundation
Abstract
=
We
developed an innovative approach to the modern physics laboratory <=
span
style=3D'position:absolute;top:28.49%;left:10.86%;width:96.62%;height:4.0%=
'>course
that allows different students to pursue different lines of research. Students
follow a “track” in which they conduct a sequence of
![](3D"slide0003_image003.gif")
The
traditional modern physics lab
ØStudents w=
ork
individually (or in small groups) on classic
experiments.
<=
span
style=3D'font-size:133%'>ØThe investigations are in no particular order. &#=
13;
<=
span
style=3D'font-size:133%'>ØStudent learning is gauged through lab reports.
Example Student Investigations=
Millikan Oil Drop Experiment&=
#13;
ØX-ray diffraction
ØFranck-Hertz Experiment
ØGamma Ray Spectroscopy
ØHall Effect
ØDoppler Shift of Light
Problems
with the traditional modern lab
=
<=
span
style=3D'position:absolute;top:15.25%;left:14.41%;width:79.4%;height:4.0%'=
>•Random
order of conceptually and physically unrelated experiments
with varying non-similar equipment.
=
<=
span
style=3D'position:absolute;top:27.25%;left:14.41%;width:93.82%;height:4.0%=
'>ØLeads to the students developing a minimalistic
approach to laboratory – “tell me what I need to
know, how to do it, and how to tell you about it.”
<=
span
style=3D'visibility:hidden'>Ø
<=
span
style=3D'position:absolute;top:43.25%;left:14.41%;width:86.7%;height:4.0%'=
>ØLeads to cook-book style procedures (to get stud=
ents
through the investigation and keep the equipment safe).
<=
span
style=3D'visibility:hidden'>Ø
<=
span
style=3D'position:absolute;top:55.25%;left:14.41%;width:91.01%;height:4.0%=
'>ØIf the instructor tells the student what to meas=
ure,
how to measure it, and what graphs and analysis should be
made, it is hard to gauge the student’s learning.
Does the student understand the physical concepts or
has the student only learned how to follow the directions?
<=
span
style=3D'visibility:hidden'>Ø
<=
span
style=3D'mso-special-format:bullet;position:absolute;left:-3.68%;font-fami=
ly:
Wingdings'>ØKnowledge learned in one lab is of no great use =
in
following labs.
Problems
with the traditional modern lab
=
ØUnless
the instructor is very aggressive, students borrow information without
necessarily understanding it. The
internet is robust with good and bad information concerning these
experiments.
Ø
ØRe-phrasing
(parroting) introductory material from the lab write up is not
the same as understanding it.
1)
•Since the experiments are classic, there is =
an
overabundance of information which may or may not =
be
accurate.
•Students tend to
concentrate more on the measured
values rather than the data’s meaning and an
understanding of the physics.
•<=
/span>
•Student’s do not
understand the rationale to cookbook data analysis. They follow the instructi=
ons,
but they give little thought as to why the analysis is done that
way.
•Students wish to compa=
re
to accepted values as opposed to doing error analysis.
=
ØStudents believe that any measurement within 5% =
of
the accepted value is excellent no matter the accuracy and precis=
ion of
the equipment.
II)
1)
Problems
with the traditional modern lab
How
we approached the Problem
•<=
/span>Rather
than have a series of independent, unrelated experiments that each
student completes, we chose to have “tracks.”
•<=
/span>Tracks
are a series of closely related investigations. Typically the investigations
have a common conceptual core.
•The
initial investigations are designed either to provide the students with a
conceptual background to the investigation through a simple mechanical
analog or to provide insight in how a key piece of equipment operates.
•<=
/span>We
provide the students with a series of guiding questions that they <=
span
style=3D'position:absolute;top:59.75%;left:11.98%;width:93.63%;height:4.0%=
'>might
be asked for a single investigation. They are provided with some background
information, but there are NO SPECIFIC DIRECTIONS on what
to do. We expect them to do =
some
research and think.
•<=
/span>Rather
than allow the students to hide behind a written report, we require
poster sessions. The depth o=
f a
student’s knowledge is obviously revealed in an interactive
exchange.
•Students gain expertise
with a particular technique and set of equipment
•The earliest experimen=
ts
don’t use expensive equipment which allows us to move
away from cook-book write-ups without endangering the equipment.
•Knowledge from one
experiment is useful in future investigations.
•Students will repeat an
experiment if their initial performance is unsatisfactory.
•Students gain
independence.
Six different tracks (currently)
=
1.Nuclear Physics=
3;
2.Molecular
Spectroscopy
3.Atomic
Spectroscopy
4.Fourier Analysis a=
nd
Fourier Spectroscopy
5.Resonance (ESR and
NMR)
6.Lasers
=
•Students are not
personally exposed to a wide array of phenomenon and =
techniques
except through discussion with other students
Under Development: Raman Spectrosc=
opy
and Laser Frequency Doubling
Molecular =
Spectroscopy
Spectrometer
Construction
of a spectrograph
1/2m
monochromator
Cs
Dimer spectroscopyAtomic
Spectroscopy
Fabry-Perot
Externally
locked diode laser
Spectrometer
Excitation
of Rb vapor
Fourier
Analysis
Driven
Oscillators
Michelson
Interferometer
Doppler
shift of light
Fourier
Spectroscopy
Resonance
Physics
Driven
Oscillators
LRC
circuits
Electron
Spin Resonance
Nuclear Magnetic ResonanceLaser
Physics
Sound
resonance
HeNe
Laser (aligning cavity)
Nitrogen pumped dye =
=
laser
=
Spectroscopy
of Iodine moleculesTracks Develop=
ed
Nuclear
Physics Track
Mechanical
Analog of ½ life
Histograms
of pulse heights
Gamma
ray spectroscopy
Measurement
of Cs ½ life
Example,
The Nuclear Physics Track
•<=
/span>Histograms of pulse heights.
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ØPulses due =
to
gamma rays are created using a scintillator, photomultiplier, and <=
/span>a gamma ray source.
ØAn oscillos=
cope
(set to single event trigger) interfaced with a computer, records <=
/span>several hundred pulses.
ØA histogram=
is
made of the number of events vs. each pulse height.
Ø
•<=
/span>Introduction to the Multichannel Analyzer and
Beer’s Law.
ØThe gamma r=
ay
pulses are now sent to a multichannel analyzer which performs the task of the oscilloscope and computer. Students perform gamma ray spectroscopy.
ØMultiple sh=
eets
of material (paper, lead, aluminum) are placed between the <=
span
style=3D'position:absolute;top:56.99%;left:15.35%;width:94.38%;height:3.5%=
'>source and the detector. Students study how peaks in the
histogram change as a func=
tion
of material thickness.
Ø
•<=
/span>Mechanical equivalent of nuclear decay.
ØA plastic t=
ray
(with a small hole) is filled with ball bearings and vigorously shaken.
ØThe time fo=
r a
particular ball bearing to exit through the hole is random.
ØThe number =
of
ball bearings in the tray is exponentially related to time.
Ø
•<=
/span>Half life of Cs
Poster
Sessions rather than of Lab Reports
Posters
serve four purposes:
1.Provide an assessment of how well each student
understands his/her investigation and track.
2.Provide professors with insight into student
misconceptions of the physics
3.Reveals
“holes” in student understanding of introductory materi=
al.
4.Provides information about each track to the stude=
nts
doing other tracks.
5.
Proces=
s of
poster sessions
•<=
/span>To alleviate student concerns about the first post=
er
session we instituted a pre-poster session. Students prepare a poster and then professors ask
questions. In the pre-poster
session students do not
answer the questions. This a=
llows
students to gauge their own understanding without any embarrassment; only the student knows whether he/s=
he
could answer the questions. =
All
students attend this pre-p=
oster
session.
=
•
•<=
/span>The first poster presentations involve only the st=
udents
who performed that particular experiment and the professors.
Now the students have to answer questions to the best of their
abilities.
•<=
/span>Professors questions tend to delve into the
student’s understanding.
•<=
/span>In later poster sessions (3), students observe the
professors asking questions, and in the last session, students ask questions first (then the
professors).
•<=
/span>Students learn what questions to ask.
<=
/span>
•<=
/span>As there is a quiz at the end of each open session,
students are motivated to ask each other questions.
Our
observations
•<=
/span>Poster sessions are an effective method for determ=
ining
student understanding.
=
;
=
<=
span
style=3D'font-size:89%'>Ø We
(professors) easily expose borrowed information that is not =
understood.
=
Ø We
feel that this method is a much better gauge than lab reports despite the use of laboratory time.
•
•<=
/span>Students are unprepared for lab.
<=
span
style=3D'font-size:89%'>ØThey don’t understand uncertainties nor the
importance of repeatability.
<=
span
style=3D'font-size:89%'>ØFundamentals of first and second semester physics =
have
been forgotten.
•<=
/span>Many students are willing to be passive rather than
active learners.
=
ØThe students do not want to think about the physic=
al
concepts involved in their
investigation.
<=
/span>
<=
span
style=3D'font-size:89%'>ØThe students do not want to think about what they =
are
measuring.
•Students, while initially resistant to the process=
, find
it refreshing to have labora=
tories
which are not solely following directions.&#=
13;
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