Lillian C. McDermott
29
History
3/15/10
or as a post-test in standard lecture/laboratory courses.
Performance by high school
physics teachers and university science (non-physics) faculty has also been at about 15%.
When given to graduate TAs and physics post-docs, the success rate has been about 70%.
We have identified several specific difficulties.
The two most common and
persistent are (1) the apparent belief that the battery is a constant current source and (2)
the apparent belief that current is “used up” in a circuit.
Individuals who made this error
often could state that “current is conserved.”
Although some could use a memorized
formula (such as Ohm’s Law) to rank bulb brightness, they had not developed a
conceptual model that they could apply to a variety of electric circuits.
68
The poor
performance of the UW introductory physics students has been confirmed at other
universities, including Harvard, where Eric Mazur found that students who could apply
Kirchhoff’s Rules to complex circuits often did poorly on qualitative questions on much
simpler circuits.
69
The findings reported above were in marked contrast to the results from K-12
teachers on similar problems after they had worked through the
Electric Circuits
module
in
Physics by Inquiry.
The process of model building
in
PbI
begins
with having the
students explore the behavior of batteries and bulbs.
They determine the conditions for a
bulb to light and construct an operational definition for a complete circuit.
Using
brightness as an indicator that there is a flow of something in the circuit, they draw
inferences from their observations to construct the concepts of current and resistance.
They use inductive and deductive reasoning to derive a set of rules that enable them to
predict bulb brightness in many resistive circuits.
As they apply their model for current to
circuits of increasing complexity, the need for other concepts (
e.g.,
potential difference)
becomes apparent.
The concepts of power and energy are introduced to account for later
observations.
(We follow Arnold Arons’ maxim, “the idea first, the name afterwards.”)
Thus, the students gradually develop a conceptual model that enables them to predict and
explain the brightness of bulbs in all resistive circuits.
Virtually all K-12 teachers who
have worked through this material in
PbI
have done very well (~ 100 %) on the post-test
shown in the following diagram.
68
Although bulbs are non-ohmic devices, application of Ohm’s Law gives the correct ranking.
69
E. Mazur,
Peer Instruction: A User’s Manual
(Prentice Hall, Upper Saddle River, NJ, 1997), pp. 5-7.
Lillian C. McDermott
30
History
3/15/10
Assessment of student learning
Virtually all teachers (K-12) develop a model that they
can apply to relatively complicated dc circuits.
A
B
C
D
E
E > A = B > C = D
Post-test on resistive electric circuits.
As in most of our research, there are important implications for instruction.
For
scientific concepts to be useful to students, they should be able to apply them to actual
objects and events.
The pretest on electric circuits is one of many questions that
demonstrated that science and engineering majors who can readily manipulate formulas
often cannot do the reasoning required to apply them correctly.
Given the constraints of
large class size, extensive coverage, and rapid pace of an introductory physics course, we
wondered what we could do to improve student learning.
We were interested in evolution,
not revolution, knowing full well that a radical change in instruction was not possible.
In
1990 the opportunity arose to try a research-based approach to address the problem.
B.
Initiation of Tutorials
The tutorial project was an outcome of the 1990
Entry Level Initiative
(
ELI
) by the
UW Provost (Laurel Wilkening) to improve the introductory courses.
Proposals were
solicited from four Departments:
Physics, Chemistry, Mathematics, and Psychology.
The
ELI
would provide ongoing funding on a competitive basis. I was on the
ad hoc
faculty
committee that met with the Chair to decide what we should do.
Peter was the graduate
student representative.
We decided to focus on the calculus-based course.
One suggestion
was to make the associated laboratory a co-requisite, instead of an independent entity.
Another idea was to replace one of the four weekly lectures in that course with small
sections led by TAs.
I remember stating emphatically that, if we were going to have
small-group instruction, it should offer more than mini-lectures and practice in solving
