Invited talk at PLT2000, Stuttgart, September 2000
25 YEARS OF LABORATORY TEACHING AT DELFT
UNIVERSITY OF TECHNOLOGY
E. LAGENDIJK
Department of Applied Physics, Delft University of Technology
Lorentzweg 1, 2628 CJ, The Netherlands
E-mail: e.lagendijk@tnw.tudelft.nl
Abstract
In the sixties, when I was a student at Leiden University, an American professor walked through the
teaching laboratory and remarked in passing: "So, this is the museum!"
Has anything changed since then?
25 years ago, when I started my career as an instructor at Delft University of Technology, the impression of
a museum was not gone. In particular, a deeper look at teaching methods revealed the traditional way of
implementing the teaching laboratory: demonstrations of theory in cookbook style. However, thanks to the
students of the late sixties (those were the days!), the times had changed: open projects had made their
appearance.
I will comment on these changes and how the teaching laboratory looks at present. Although predictions
are difficult, especially if they concern the future, I will also say something about the future of the teaching
laboratory as I see it.
1. From the past to the present
Figure 1 shows two portraits: one of me, the physicist as a young man and one of a first
year student nowadays, both doing the same experiment. Do you see the differences?
This question reminds me of that daily problem in my holiday newspaper Nice Matin:
"Les sept erreurs", which I once tried to solve at breakfast sitting in the sunshine,
croissants within my reach. Rather difficult to find "les erreurs"!
Figure 1. Left: me doing the pendulum experiment
in the sixties, right: one of my students doing it now.
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2. THEORIE
Voor de kinetische energie Ek en de potentiële energie Ep gebruiken
we de volgende uitdrukkingen:
1 2
mv
2
E p = mgh
Ek =
4. INSTRUMENTATIE
De slingeropstelling is afgebeeld in figuur 2.
(1)
(2)
welke als volgt herschreven worden:
2
1
 d 
m 2 

2
 dt 
E p = mg 1 - cos a 
Ek 
(1a)
(2a)
De uitwijkingshoek wordt hierbij uitgedrukt in radialen. De
constante som van Ek en Ep moet gelijk zijn aan de potentiële energie
bij de maximale uitwijking ao, omdat dan de snelheid en dus Ek nul is.
Daarom geldt
(3)
E k + E p = mg  1 - cos  0


dus met behulp van (2a)
E k = mg cos  - cos  0

(4)
Uit formule (4) volgt door gebruik te maken van formule (1a)
2g
d
cos  - cos  0 
=
dt

(5)
Aangezien wij hier da en dt als eindig mogen beschouwen kan voor
(5) ook geschreven worden
d
dt 
(5a)
2g
cos   cos  0 

Als t = 0 gekozen wordt voor een tijdstip waarop a = 0, dan wordt ao
bereikt na ¼T; voor de periode T geldt dus
ao
T =4
d

(6)
2g
cos  - cos  0 

0
De integraal in (6) is niet analytisch op te lossen maar wel met behulp
van reeksontwikkeling te benaderen. Men kan voor ao < /2 het
volgende afleiden:

1
 o  9
 o  
  1 + sin2   +
sin4   +
T = 2
. 4
 2  64
 2   (7)
g


  hogere machts termen
Figuur 2. De slingeropstelling.
Een cilindervormig voorwerp C, dat aan een metaaldraad D is bevestigd, kan slingeringen uitvoeren om het ophangpunt P. Voor de
ophanging kan uit drie constructies gekozen worden, namelijk een
vaste inklemming, een pan-en-mes constructie en een constructie die
speciaal geschikt is voor grote uitwijkingshoeken ("oog om as"). Het
geheel is bevestigd aan een stevige arm S.
Verder zijn aanwezig:
Cilinders (C) met massa's van ongeveer 50, 200 en 800 g.
Vijf metaaldraden met lengten van ongeveer 0,2; 0,4; 0,7; 1,0 en
1,4 m; draaddiameter is 0,5 mm.
Een meetlint met millimeterverdeling.
Een stophorloge.
5. UITVOERING
Metingen: met een kleine uitwijking (sin o  0,1), een massa naar
keuze en een ophanging naar keuze wordt de slingertijd bepaald voor
alle vijf draadlengtes. (Steeds vier keer twintig slingeringen.)
Bij gebruik van pan en mes en de massa van 800 g kan de uitkomst
van de inleidende meting bij l = 1,0 m mede gebruikt worden.
Uitwerking: Eerst wordt een tabel gemaakt van onderstaande gemeten
en berekende grootheden:
(i is weer het nummer van de meting)
de slingerlengte
li
de slingertijd
Ti
de grootheid
Ti2/4
de grootheid
gi (volgens formule (8a))
Vervolgens wordt een grafiek getekend van de grootheid Ti2/4als
functie van li met de volgende schaal: 0,001 s2/mm grafiekenpapier
voor Ti2/4en 5 mm/mm grafiekenpapier voor li.
Uit de richtingscoëfficiënt van de verkregen rechte volgt een waarde
voor de valversnelling, terwijl het "niet door nul gaan" iets kan
zeggen over systematische fouten in de slingerlengte.
Afwijkingen van de rechte dienen verklaard te worden.
Bij een (kleine) uitwijkingshoek ao = 0,2 radiaal, dus
sin ½ao  0,1, krijgt de uitdrukking tussen accolades de waarde
1+
1 1
9
1
.
+ .
+ ... . wat slechts weinig van 1 afwijkt.
4 100 64 10000
Voor oneindig kleine hoeken ao, dus in de limiet ao nadert tot nul,
gaat (7) over in
T = 2

g
ao  0 
(8)
waarbij voor de versnelling van de zwaartekracht volgt
4 2 
ao  0 
(8a)
T2
Figure 2. Part of the labmanual on a first year pendulum experiment in the sixties (only about 2 out
of 5 pages are reproduced here!)
g=
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Een mathematische slinger bestaat uit een puntmassa m, bevestigd aan een stijve massaloze draad die aan zijn
andere uiteinde opgehangen is aan de "vaste wereld". Het systeem puntmassa-draad kan in één vlak vrij
slingeren om het ophangpunt onder invloed van de zwaartekracht, zie figuur 1. Te bewijzen valt dat de
slingertijd T in de limiet van kleine uitwijkingshoek gelijk is aan:

(1)
g
hierin is l de lengte van de slinger en g de versnelling van de zwaartekracht.
Bepaal met behulp van formule 1 de versnelling van de zwaartekracht, gebruikmakend van de aanwezige
apparatuur. Vergelijk uw resultaat met de literatuurwaarde.
T = 2
Figure 3. Part of the labmanual on a first year pendulum experiment today. Only an obvious figure
is missing.
On a closer look, three "erreurs" may be evident. Firstly, the clocks are different, the
newer one being a digital one. This, of course, symbolizes a complete revolution in
measurement technology. In the last 25 years we have gone from analogue to digital. The
second "erreur" which may draw your attention is the pendulum construction, the newer
one being of a less sophisticated design. A pan and knife suspension is missing! This
symbolizes a revolution from demonstration to investigation. A third difference is in the
looks of the student: does anybody of your students wear a jacket and glasses nowadays?
This symbolizes a social revolution: contact lenses for everybody and formal dressing for
nobody.
Let me first comment on the second revolution, which is most important from an
educational point of view: from demonstration to investigation. This revolution becomes
much more obvious if we compare the labmanuals. Figures 2 and 3 show part of the
labmanuals in these two cases. The difference is that the older manual contains a detailed
theory and many cookbook instructions and the newer one contains only one formula and
only two instructions. To be honest, the older experiment not only requested to measure
the gravitational field strength g using small amplitude approximations, but also asked to
verify the large amplitude predictions of the theory, all in one labsession. Nowadays, this
would be a good starting point for a first year labproject. See references 1 and 2.
The difference will become even clearer if you visit our introductory laboratory.
Nowadays in many cases no instruments are put ready on the table. The student should
collect his instruments from a supply room, based on rational considerations, like wanted
accuracy. If you could stay a while, and I invite you to do so, you would also see that the
role of the assistant has changed. Instead of initialing one executed cookbook instruction
after the other, blaming the student if the result is not according to the standard answer,
he discusses the choice of instrumentation and the methods of measurement and data
processing. Questions are for example how many swings the pendulum should make to
get a reasonable uncertainty in the measured pendulum period and how pendulum length
should be varied. Can we do with a graph and a paper-and-pencil method to determine g,
or should we use a least-squares calculation? Yes, there are computers in the room and a
sophisticated plot and regression analysis program is available, Origin in our case,
manifestations of our first, digital revolution.
You might comment that the "he" in the above could be a "she" as well. Alas, one thing
didn't change: like the student, the assistant is still a he in 9 out of 10 cases! All attempts
to attract more females to the sciences, like the governmental campaign "Kies exact"
(Take Science) have failed miserably.
The change in set up is not only reflected in this single experiment, but also in the first
year laboratory as a whole. From a collection of loosely related experiments, some of
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them demonstrating experimental techniques, others demonstrating theoretical concepts,
we switched to a system of connected courses with strong emphasis on the learning of
experimental abilities, followed by free experiments ("projects"). Table 1 shows the first
year laboratory in the late sixties and in the late nineties of the twentieth century.
Table 1. Contents of the first year laboratory for physics students (1 session = 1/2 day in the lab; 1
credit point (cp) = 40 hours of study. One year of study = 42 cp). Not included are related lecture
courses on the use of computers and on electrical and electronic circuitry and instrumentation.
late sixties
late nineties
-
-
A1 Measurement of length I
A2 Measurement of length II
A8 Pyknometer
B3 Calorimetric determination of heat of
solution (or B4: heat of dilution or B5 heat of
neutralization);
- D0 Exercises on electrical instruments and
simple circuits
- D1 Measurements on circuits
- D2 Measurements of resistors in bridge circuits
- D4 Measurements using the compensation
method
- B12 The Peltier effect
- B10 Determination of surface tension
- C1 Interference phenomena
- D9 Magnetic properties of materials
- D11 Measurements on direct current machines
- E11 Determination of viscosity of fluids
- C4 Diffraction phenomena
- C6 Double refraction and polarization
- C23 Reflection, linear and elliptical
polarization
- E1 Determination of shear modulus with
torsion pendulum
- E3 Determination of elasticity modulus from
stress
(19 sessions) (excluding instruction sessions)
Labcourse on the use of computers (7 sessions,
1 cp) (see http://www.tn.tudelft.nl/icg/
cursusbeschrijving/)
- Labcourse on introductory experimentation (9
sessions, 1 cp including instructions and tests
on labsafety and introduction in
experimentation) (see http://www.tn.tudelft.nl/
qdb/tnw1401-pip/default.htm and reference 3)
- Labcourse on electrical and electronic
instrumentation (8 sessions, 2 cp)
- Two labprojects (4+5 sessions, 1+2 cp)
(29 sessions (excluding instruction sessions), 7 cp)
For details about the curriculum as a whole see:
http://www.tn.tudelft.nl/ and click "onderwijs" and
"curriculumoverzicht"
From figure 2 and table 1 the "erreurs" in comparing the sixties to the nineties are very
clear. We use fewer cookbooks and have more structure in the labcourses. The cookbook
didn't vanish completely however. For example, in the course on electrical
instrumentation a significant part consists of precooked exercises on how to use a
multimeter, how to use an oscilloscope, how to build a Wheatstone bridge etc. But the
course is concluded by an experiment, which forces the student to use the knowledge and
the abilities obtained in the previous exercises in a more or less "open" situation.
As table 1 shows, at the end of the first year real project work is included nowadays. The
topics may be classical, like double refraction or pendulum properties, but the educational
method has changed. Of course, this also gives us the opportunity to introduce modern
topics in the first year curriculum like high temperature superconductivity and chaos.
What also has been changed rather drastically is the amount of report writing. A first year
student in the sixties wrote a report on nearly every experiment, about twenty in total. A
first year student nowadays writes only four reports. However, more emphasize is laid on
making notes during the execution of the experiment and the reports are of a more mature
kind, anticipating real publications. To this end, we use Scientific Word, a Windows
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application based on LATEX. We offer a LATEX "style", so that the students can
concentrate on content, not on form.
From table 1 you can also infer the strength of the digital revolution. The labmanual of
the late sixties doesn't mention the computer at all. Computers were present then,
although not in the teaching laboratory but in computational centers, and not to be used
by first year students. The arrival of the PC has changed this radically. The PC is part of
nearly all our experiments now, at first mainly to process data acquired by hand, using
computer algebra (we use Maple) and plot and data-analysis routines like least-squares
calculations (we use Origin) and to write reports (as mentioned, we use Scientific Word).
Students learn the use of these applications in the course on the use of computers. In this
course the student also assembles a PC from components, (partly) installs and learns to
use Windows NT and Linux, learns principles of programming using Java and learns the
use of the web.
Later on, in the second year, the computer is also used for data-acquisition. We use
LabView for this purpose. In the second year we also introduce MatLab, in particular to
perform simulations. In the third year a course on object oriented programming is
planned. The third year also contains a large labproject as a preparation for the "doctoral"
(master's) project in the fourth and fifth year. Table 2 shows the laboratory program of
the second and third year as we expect it to be in 2001.
Table 2. Second and third year physics labcourses expected to be operational at TU Delft in 2001
Second year
Third year
-
-
-
Labcourse on transport phenomena (6 sessions,
1 cp)
Labcourse on data-acquisition and dataprocessing (14 sessions, 3.5 cp)
Course on MatLab and simulation with MatLab
(7+7 sessions, 1+1 cp)
-
Labcourse on wave phenomena (9 sessions, 1.5
cp)
Course on object oriented programming (2 cp)
Labproject (6 cp)
The third revolution, the social one, may seem one of outward appearance only: jackets
and glasses have gone. It is not. In the late sixties, in the spirit of the Paris revolt, students
began to protest against the cookbook. They overtly copied reports because, as they
rightly remarked, the best thing to do to get a high mark was to give precooked answers
to precooked questions. They cried for projects with an emphasis on social context. So
the third revolution was the driving force of the second! The social context has largely
disappeared from our physics teaching laboratory, together with flower power and long
hair, but the projects have stayed. They now mainly serve as a preparation for research
and development in the master's stage and eventually in science and industry. In other
parts of the curriculum there are clear remains of the third revolution as a social
movement in the form of courses on the history, the philosophy, the ethics etc. of science.
2. Into the future
Is the future ours to see? Figure 4 shows the number of students matriculated in Applied
Physics at Delft University of Technology as a function of the year of matriculation.
Linear extrapolation from the year 1987 shows the number to be zero in 2007. That's the
bad news. The figure also shows the percentage of female students. This number is an
educational constant from 1987 within statistical fluctuations. That also is bad news,
because the participation of female students at Dutch universities is increased to about
50% and still slowly increases. The good news is that even if the number of students
drops to zero, about 10% of this number still will be female.
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100
200
80
150
60
100
40
50
20
% female
Number of first year TN students
250
0
0
1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000
year
Figure 3. Matriculation of physics students in Delft (squares, left scale), and participation of females
(triangles, right scale)
There is no corresponding decline in total student numbers at Dutch universities. Other
physics departments also show declining student numbers. So there is a real shift of
interest from physics to other disciplines. We have lost our glamour. No longer good old
Einstein is somebody to be!
So is there any future for our beloved discipline?
The decline is a general phenomenon, not only at Dutch universities but worldwide. And
worldwide is the solution: mix the disciplines or, as some physics hard-liners call it,
muddy the waters. This year, applied physics, chemical technology, material technology
and biotechnology offer a common first year in Delft. As a consequence, the content of
the labcourses in table 1 is shifted towards the other disciplines and one of the labprojects
is sacrificed to give room to labcourses in chemistry etc. Shifts in the theory courses, in
particular those related to the labcourses, are even bigger. Only the future can tell us
whether this will stop the fall of student numbers. In particular, will this "softening"
(from the physicist point of view!) attract more females and more non-natives?
A complication is that at the same time secondary education in Holland undergoes a
major revision in content as well as in method. The content change is one from less
knowledge to more abilities. This means that incoming students have less knowledge of
hard core mathematics and physics. Coulomb's law is no longer an explicit part of the
syllabus! The methodical revision is the introduction of the so-called "study house" as a
(partial) replacement of "frontal teaching". Problem and learner centered learning
replaces content and teacher centered teaching. This may be advantageous for us,
labteachers, because the student is better trained in doing investigations on one's own. So
I expect that the trend to more project work will continue.
It is not difficult to predict that the IT business will go on to boom in the future. More
digital intelligence in less space at lower prices will be available to everybody, stand
alone and via the web. The student simply plugs in, wireless if wanted, to get information
and to process data. Books, publications, lecture notes, manuals, applications for dataacquisition and -processing, all is electronically delivered on demand, not only visually
on screen but also by speech and in any language. The screen will be full of moving
pictures. Interactive simulations and movies will be the rule instead of the exception.
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Communication between learner and teacher will be web-oriented. To get a glimpse of
the future, visit the web sites cited in the references 4 to 7. In the end I expect that the
main task of a lecturer will not be to produce lecture notes and to read these meticulously
at mass meetings. Instead he or she guides the students to good web sites, gives them
problems and assesses their responses using electronic means. Small group teaching and
learning, formal or informal, will blossom, in problem-oriented sessions. These groups
may gather in multi-media surroundings, including web and laboratory facilities to take
integrated courses. This is called the "studio-classroom" concept, see reference 8
So, at last, the frequently announced death of the mass lecture is in sight. Or isn't it? And
the pendulum will only swing on screen. Or won't it?
I think that some of the mass lectures will survive as social gatherings, as appetizers and
activators, with stars as guest lecturers and striking demonstrations, more a play than a
reading. If we do this well and make them widespread by broadcasting them, some of our
glamour may return.
I think, and this may be wishful thinking, that apart from these multimedia courses
accompanied by "master" lectures the teaching laboratory will keep its place by and large
as it is today in Delft. It will give the opportunity to train experimental abilities as a
preparation for research and development. So the pendulum will swing forever not only
on screen but also in a real laboratory and we labteachers will be in need to guide
students in exploring the secrets of nature.
Literature
1. R.A. Nelson, and M.G. Olsson, “The pendulum - Rich physics from a simple
system”, Am. J. Phys., 54, pp. 112-121 (1986)
2. E. Bulur, S.Ö. Aniltürk, and A.M. Ölzer, “Computer analysis of pendulum motion:
An alternative way of collecting experimental data”, Am. J. Phys., 64, pp. 1333-1337
(1996)
3. E. Lagendijk, and E de Wolff, "A computer based teaching Package in Introductory
Experimental Physics", Proceedings of CBLIS '99, Enschede, The Netherlands,
University of Twente
4. A pendulum lab on the screen:
http://monet.physik.unibas.ch/~elmer/pendulum/index.html
5. A lecture course on the screen:
http://physics.harvard.edu/lecturse/lecturesb00.html
6. Java applets on the screen:
http://physicsweb.org/resources
7. Much physics software on the screen:
http://physlink.com/software
8. The studio classroom concept is developed at Renselaer Polytechnic Institute
http://www.ecse.rpi.edu/Courses/Cestudio/index.html. See also
http://cde.rpi.edu/wilson.html
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