EDSE 732 SECONDARY SCIENCE METHODS
4/17/10
Lesson Plan – Nature of Science
Moritz Huegle
1. Topic of the lesson
Georg Simon Ohm and his discoveries
This lesson will address the nature of science focusing on the life of G.S. Ohm, on his
experiments and discoveries and on the problems he had.
2. Class
The lesson plan is taken from a unit about the concept of the electrical resistance in
physics. It is designed for an eleventh grade physics classroom. The students are
familiar with the connection of current, voltage and resistance as described in Ohm’s
law.
3. Standards
Students evaluate conclusions looking at historic set ups and instruments mainly based
on qualitative data such as instrument malfunction or human error. They also look at the
experimental results of the experiments made many years ago. (Standard P-1.4 and P1.7)
When looking at the technological design of the instruments that were used many years
ago they evaluate them in terms of creativity, materials, time and cost (Standard P-1.8)
4. Objectives
•
Students should be able to understand that scientific laws are different from
mathematical laws and thus not ‘set in stone’
•
Students should be able to explain the use of creativity and imagination in
scientific research
•
Students should be able to understand the importance of fellow scientists as well
as the difficulties that come with them
•
Students should be able to present their results on a transparency in class
•
Students should be able to develop further social competences. They see the
importance of individual effort during group work and respect each other’s
results. They also engage actively in classroom discussions.
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Lesson Plan – Nature of Science
Moritz Huegle
5. Context
The present unit is about the electrical resistance. The definition was introduced earlier.
The last two lessons focused on resistance, voltage and current in series and parallel
circuits. Students examined the quantities in both circuits coming up with the relationship
expressed in Ohm’s law. They used the formula U=R*I to calculate missing quantities in
series and parallel circuits and applied their knowledge to more complex circuits. The
functionality of a current divider, a voltage divider and a potentiometer was addressed in
a jigsaw in the last lesson.
The students can build series and parallel circuits measuring the three important
quantities safely. In addition to that they are able to apply Ohm’s law; they can calculate
current, voltage and resistance and series and parallel circuits. But it is also important
that they not only apply the math using formulas and calculators but also understand the
concept of Ohm’s law. The experiment the students were doing required some creativity
but the outcome was known and the experiments had already been done before.
Scientists as G.S. Ohm often come up with experiments nobody never did before. They
come up with ideas that were knew and thus discovered unknown connections in
science. The importance of creativity and imagination, the opposition some scientists
might encounter and the concept of laws and mathematical descriptions should be clear
to students as well. This lesson will provide the students with the opportunity to get a
general understanding of the topics mentioned above and is designed to sensibilize the
students and to put their understanding of the subject of resistance on a higher level
including it in the bigger picture of science.
The knowledge they gain in this lesson should help them to apply the learnt concepts to
different subjects understanding the physics more deeply.
6. Materials
Items per class
-
classroom with access to at least one computer for every two students
-
model of the torsion balance and transparency with picture and short description
of the torsion balance
Items per student
-
Reading material on the history of Ohm’s law
-
Homework work sheet
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EDSE 732 SECONDARY SCIENCE METHODS
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Lesson Plan – Nature of Science
Moritz Huegle
7. Instructional Sequence
Time
in
Min
Section
Methods
media
Planned process and activities
.
5
Introduction
A student gives a presentation on Georg Simon
Presentation
Ohm focusing on his life and surroundings not
talking about his discoveries
OHP or
Beamer or
Blackboard
5
Introduction
A student presents Georg Ohm’s fellow
Presentation
scientists (e.g. Alessandro Volta, Thomas
Johan Seebeck)
OHP or
Beamer or
Blackboard
15
Discussion
T shows the transparency with the Ohm’s
torsion balance and a short description (see
addendum 10.1)
If possible T would bring a model of the torsion
frontal
instruction
transparency
balance to the lesson
How did Ohm construct this instrument, whose
inventions did he use, did he have a plan how
to build it?
Students are handed some reading material
and encouraged to use the internet for further
information
40
Students read the material on the experiments
Individual
Development
and instruments G.J. Ohm came up with
student work
and
browse the internet for more information and
(possibly
Research
write down notes on the questions (see
partner work)
addendum 10.2)
Work sheet
and computer
20
Collection
The following questions are discussed in class:
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Lesson Plan – Nature of Science
Moritz Huegle
Where do you think did Ohm use creativity and
imagination during his work?
Why was his work not appreciated by other
scientists?
What influences helped or limited Ohm’s work?
5
Homework
Is Ohm’s law really a law? (see addendum
Work sheet
10.3)
8. Assessment
During the discussion the teacher is using formative assessment by addressing the
student’s understanding with questions. The central questions can be seen in the
instructional sequence. The actual questions asked can be modified by more narrow
questions depending on the understanding of the students.
The homework addresses another point bringing some of the aspects discussed in class
together. The students are asked to apply their understanding of physical laws to Ohm’s
law. The homework will be collected at the beginning of the next lesson and reviewed.
9. References
National Science Education Standards (1996)
Retrieved August 23, 2009, from The National Academies Press
Web Site: http://www.nap.edu/openbook.php?record_id=4962
South Carolina Curriculum Standards (2005)
Retrieved August 23, 2009, from South Carolina Department of Education
Web Site: http://ed.sc.gov/agency/Standards-and-
Learning/AcademicStandards/old/cso/standards/science/
http://www.sn.schule.de/~gyfloeha/rt/lex03/ohm.html
http://www.geocities.com/bioelectrochemistry/ohm.htm
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EDSE 732 SECONDARY SCIENCE METHODS
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Lesson Plan – Nature of Science
Moritz Huegle
10. Addendum
10.1. Transparency
The picture shows Ohms torsion balance with which he could measure the current flow in
wires and determine its resistance. For the generation of electricity he used a horseshoeshaped thermo-element made from bismuth with copper rods attached to its legs. If one
end (a) was dipped in a bowl with ice water and the other (b) in boiling water the metal
handle would provide a constant voltage. Two cups of liquid mercury (c d) were used as
electrical switches. The current was passed through the tensioned wire (s). Above the
wire was a magnetic needle (f) suspended from a glass cylinder. The scale was adjusted
before the measurement so that wire and the needle pointed exactly in the north-south
direction. The more current was sent through the wire, the stronger the magnetic needle
was deflected out of the north-south direction. An adjusting device (g) at the top of the
instrument was used to return the deflection of the needle to the north-south direction.
The deflection, which Ohm took as a dimension for the amount of current could be read
out on a scale.
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Lesson Plan – Nature of Science
Moritz Huegle
10.2 Reading material
Source I: (A little history about Ohm - http://ffden2.phys.uaf.edu/211.fall2000.web.projects/Jeremie%20Smith/page2.htm )
Georg Simon Ohm was a German physicist born in Erlangen, Bavaria, on March 16,
1787. As a high school teacher, Ohm started his research with the then recently
invented electric cell, invented by Italian Conte Alessandro Volta. Using equipment of his
own creation, Ohm determined that the current that flows through a wire is proportional
to its cross sectional area and inversely proportional to its length. Using the results of his
experiments, Georg Simon Ohm was able to define the fundamental relationship
between voltage, current, and resistance. These fundamental relationships are of such
great importance, that they represent the true beginning of electrical circuit analysis.
Unfortunately, when Ohm published his finding in 1827, his ideas were dismissed by his
colleagues. Ohm was forced to resign from his high-school teaching position and he
lived in poverty and shame. However, his research efforts gained allot of support outside
of Germany. In 1849, Georg Simon Ohm was finally recognized for his efforts by being
appointed as a professor at the University of Munich.
Source II: (Georg Simon Ohm http://www.geocities.com/bioelectrochemistry/ohm.htm )
As was the custom of the time, he [Georg Simon Ohm] sent the manuscript to King
Wilhelm III of Prussia upon its completion. The King [Wilhelm III of Prussia] liked Georg's
work and on 11 September 1817 he offered Ohm a position at a Jesuit Gymnasium. […]
Luckily, the physics lab was well-equipped, so Ohm devoted himself to learning some
physics. Being the son of a locksmith, Georg had some practical experience with
mechanical equipment. He enjoyed making accurate apparatus and once, after making
one accurate, but simple, device he remarked that, "I feel clearly that only that which is
simple can be great." His claim certainly foreshadowed his later achievements in
simplifying the theory of electric circuits.
This apparatus [torsion balance on the transparency] was used by Ohm. Current flowing
through the metal bar in the center cylinder deflects a magnetized needle suspended
above it. The deflection angle is proportional to the current. The source of electric
potential is a thermocouple (discovered by Seebeck in 1821). The ends of the
thermocouple are heated by steam and cooled by ice-water in the small containers on
the tripods. The use of a thermocouple made the measurement possible; other sources
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Lesson Plan – Nature of Science
Moritz Huegle
of potential available in the 1820's were too unreliable.
As he had done for so much of his life, Ohm continued his private studies reading the
texts of the leading French mathematicians Lagrange, Legendre, Laplace, Biot and
Poisson. In 1820 Oersted discovered electromagnetism, and shortly afterwards,
Becquerel and Barlow began their researches into the conductivity of various metals.
Everywhere experimenters were making new discoveries in the young science of
electricity. Yet there was also much confusion. Terms like 'tension', 'intensity', 'quantity',
and 'exciting force' were used to describe various attributes of electricity, but no one was
clear about the exact meanings of the terms and their relationships. At this same time,
Ohm was becoming depressed. He had taught for many years and now was
overburdened with students. He hadn't landed the university position that all
mathematicians yearn for, and he finally realized that he would never marry. In short, he
felt his life had reached a dead end. In 1825 he decided to renew his outlook and devote
himself to research in electricity.
At first his experiments were conducted for his own educational benefit as were the
private studies he made of the works of the leading mathematicians. To begin his
researches, Ohm started with a series of three experiments. In the first, he measured the
'intensity' of electricity in a wire connected between the terminals of a voltaic pile. To
measure the intensity he measured the deflection in a magnetic needle held over the
wire. (He later improved the method by attaching the needle to a torsion balance.) Ohm
was looking for a relationship between the measured intensity and the length of the wire.
His decision to measure the loss in intensity rather than the intensity itself led him to a
logarithmic relation which held only because of the high internal resistance of the voltaic
pile. The pile was very cumbersome. There was an initial surge of current and the fast
polarization caused the voltage to decrease steadily. He therefore had to devise
elaborate methods for normalizing his data. In the third experiment, Ohm took the advice
of a colleague and replaced the voltaic pile with a thermopile.
In the second of the series of experiments, Ohm determined the lengths of wires, made
from different metals, that gave the same current. Ohm called these various lengths
'equivalent lengths.' Once Ohm put this experimental results together and decided to
consider measuring actual intensity rather than loss in intensity, he was able to phrase
his famous law in the form I = E/R.
The Jesuit Gymnasium of Cologne failed to continue to keep up the high standards that
it had when Ohm began to work there so, by 1825, he decided that he would try again to
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Moritz Huegle
attain the job he really wanted, namely a post in a university. Realising that the way into
such a post would have to be through research publications, he changed his attitude
towards the experimental work he was undertaking and began to systematically work
towards the publication of his results:
"Overburdened with students, finding little appreciation for his conscientious efforts, and
realising that he would never marry, he turned to science both to prove himself to the
world and to have something solid on which to base his petition for a position in a more
stimulating environment."
In fact he had already convinced himself of the truth of what we call today "Ohm's law"
namely the relationship that the current through most materials is directly proportional to
the potential difference applied across the material. The result was not contained in
Ohm's firsts paper published in 1825, however, for this paper examines the decrease in
the electromagnetic force produced by a wire as the length of the wire increased. The
paper deduced mathematical relationships based purely on the experimental evidence
that Ohm had tabulated.
Ohm made only a modest living and as a result, his experimental equipment was
primitive. Despite this, he made his own metal wire, producing a range of thicknesses
and lengths of remarkably consistent quality. For the nine years he spent at the Jesuit's
college, he did considerable experimental research on the nature of electric circuits. He
took considerable pains to be brutally accurate with every detail of his work. Ohm was
afraid that the purely experimental basis of his work would undermine the importance of
his discovery. He tried to state his law theoretically but his rambling mathematical proofs
made him an object of ridicule.
In two important papers in 1826, Ohm gave a mathematical description of conduction in
circuits modelled on Fourier's study of heat conduction. These papers continue Ohm's
deduction of results from experimental evidence and, particularly in the second, he was
able to propose laws which went a long way to explaining results of others working on
galvanic electricity. The second paper certainly is the first step in a comprehensive
theory which Ohm was able to give in his famous book published in the following year.
What is now known as Ohm's law appears in this famous book "Die galvanische Kette,
mathematisch bearbeitet" (The Galvanic Circuit Investigated Mathematically) (1827) in
which he gave his complete theory of electricity.The book begins with the mathematical
background necessary for an understanding of the rest of the work. While his work
greatly influenced the theory and applications of current electricity, it was coldly
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Moritz Huegle
received. We should remark here that such a mathematical background was necessary
for even the leading German physicists to understand the work, for the emphasis at this
time was on a non-mathematical approach to physics. We should also remark that,
despite Ohm's attempts in this introduction, he was not really successful in convincing
the older German physicists that the mathematical approach was the right one. To some
extent, as Caneva explains, this was Ohm's own fault:
"... in neither the introduction nor the body of the work, which contained the more
rigorous development of the theory, did Ohm bring decisively home either the underlying
unity of the whole or the connections between fundamental assumptions and major
deductions. For example, although his theory was conceived as a strict deductive
system based on three fundamental laws, he nowhere indicated precisely which of their
several mathematical and verbal expressions he wished to be taken as the canonical
form."
It is interesting that Ohm's presents his theory as one of contiguous action, a theory
which opposed the concept of action at a distance. Ohm believed that the
communication of electricity occurred between "contiguous particles" which is the term
Ohm himself uses. The paper is concerned with this idea, and in particular with
illustrating the differences in scientific approach between Ohm and that of Fourier and
Navier.
Ohm's famous law states that the flow of current is directly proportional to voltage and
inversely proportional to resistance. Using this law, scientists could for the first time work
out the amounts of current, voltage and resistance in electric currents, and the variations
of one through changes in the others. By altering circuit components such as
resistances, they could then design circuits to perform specific functions. His formulation
of the relationship between current, electromotive force, and resistance, is the basic law
of current flow.
Source III (Georg Simon Ohm http://www.geocities.com/bioelectrochemistry/ohm.htm )
Unfortunately, Ohm's law was met with resistance. Many of his countrymen were used to
experimenting with voltage and current, but they considered these to be entirely
separate phenomena. Now Ohm was claiming a connection between the two. Ohm's
work was also ignored in administrative channels due, perhaps, to his brother, Martin,
who was continually criticizing the ministry of education. The Prussian minister of
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Moritz Huegle
education announced that "a professor who preached such heresies was unworthy to
teach science." Unfortunately, Georg was caught in the ensuing political storm. One
science 'critic' reviewed Ohm's book, claiming that its "sole effort is to detract from the
dignity of nature." This hinted at the Hegelian philosophy that was just then sweeping
German science. Ohm's feeling were hurt, he decided to remain in Berlin and, in March
1828, he formally resigned his position at Cologne. He took some temporary work
teaching mathematics in schools in Berlin.
He accepted a position at Nüremberg in 1833 and although this gave him the title of
professor, it was still not the university post for which he had strived all his life. For
whatever reasons, Ohm's work was accepted abroad before it was in his own country.
Joseph Henry in America recognized that Ohm had cleared away nearly all the
confusion surrounding electrical circuits. His work was eventually recognised in England
by the Royal Society with its award of the Copley Medal in 1841 with the inscription "he
had clarified in a remarkable way what had been previously wrapped in mystery and
confusion." He became a foreign member of the Royal Society in 1842. Other
academies such as those in Berlin and Turin elected him a corresponding member, and
in 1845 he became a full member of the Bavarian Academy.
This belated recognition was welcome but there remains the question of why someone
who today is a household name for his important contribution struggled for so long to
gain acknowledgement. This may have no simple explanation but rather be the result of
a number of different contributary factors. One factor may have been the inwardness of
Ohm's character while another was certainly his mathematical approach to topics which
at that time were studied in his country a non-mathematical way. There was undoubtedly
also personal disputes with the men in power which did Ohm no good at all. He certainly
did not find favour with Johannes Schultz who was an influential figure in the ministry of
education in Berlin, and with Georg Friedrich Pohl, a professor of physics in that city.
Questions:
1. Have you found further information about the function of the torsion balance?
2. Being a teacher do you think that Ohm lived a wealthy live that helped him do his
research?
3. Which resources did he use for his experiments?
4. Did anyone help him with the set up of the experiments, the data collection and
the conclusions?
5. Which difficulties did he face publishing his results?
10.3 Homework
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Lesson Plan – Nature of Science
Moritz Huegle
Read the following discussion between two physicists about Ohm’s law and try to
explain why Ohm’s law is not a physical law that infers from any effects of nature but is
rather a definition formula for an idealized resistance.
Physicist I: Does an experimental verification of Ohm’s law exist?
Physicist II: That is such a dumb question! Everyone knows that the famous physicist
Gerog Simon Ohm approved it a million times in experiments. Even teenagers can verify
it easily in experiments.
Physicist II: Is it actually checked? With which fault tolerances is it checked? How does
such a check work?
Physicist I: It’s not that easy! I take a metallic conductor put a constant voltage at the
ends of the conductor and then I measure the current through the conductor. After that I
increase the voltage by 10% and measure the current again. I will notice that the current
increased by 10%. This shows the proportionality between voltage and current and
Ohm’s law is approved.
Physicist II: Is this still true if I increase the current so much that the conductor heats up
noticeable?
Physicist I: Well, of course not because of the temperature-coefficient of the conductor.
Physicist II: Is this still true if I use a semiconductor instead of a metallic conductor?
Physicist I: Of course not!
Physicist II: Is this still true if a use alternating current?
Physicist I: Of course not because of the self-inductance of the conductor!
Physicist II: Then when does Ohm’s law apply?
Physicist I: Yeah…take a special resistance wire called constantan-wire. It has no
temperature-coefficient at all and you can strictly apply Ohm’s law!
Physicist II: Is this still true if I increase the current so much that the melting point of the
constantan-wire is passed due to the lost heat?
Physicist I: Of course not!
Physicist II: Then when does Ohm’s law apply?
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