The Logic of Physics
Dr Judith Pollard and Peter Veitch
Department of Physics and Mathematical Physics
"Reproducing algebra is not the same as understanding the logical structure of a physics argument"
Background | Aims | Process | Evaluation Contact
Background
Most teachers, irrespective of discipline, hope that their students are understanding the subject matter at hand and not merely reproducing material for the sake of passing the subject or course. Unfortunately, assessment methods often fail to discriminate between deep and superficial learning, and since the latter is often easier, assessment can drive students to learn superficially. Many articles and books on learning and teaching exhort teachers to use methods of instruction and assessment that develop and reward deep understanding, but what would these look like? The following is a short account of how this problem was tackled within the Physics discipline.
A large part of the lecture time in a conventional calculus-based subject is devoted to derivation of results by applying general principles of physics to systems of interest. The students’ understanding of these derivations may be tested with an examination question such as:
Use Gauss's law to find the electric field just outside a conducting surface carrying charge density per unit area
Typically, student responses indicate that they do not understand the core concepts or the logical structure of the physics. Furthermore, assessment procedures that do not discriminate between answers given by rote and those based on an understanding of the concepts can perpetuate the problem. Research built on these observations (Pollard, 1993), where students were invited to 'think aloud’ as they worked through some problems, confirmed that most students distorted the logic required to understand and answer the questions and were unaware that they were doing so.
Consequently, we made some simple modifications to the way physics questions for tutorials were structured that encouraged students to explore the concepts of physics and how they are related. This approach is clearly relevant to those subjects, such as mathematics, chemistry and engineering, where students easily fall into the trap of substituting rote learning for understanding.
Aims
To improve:
- The extent to which students understand the logical structure of physics in general, and the logical development of derivations in particular
- The validity of assessment of this aspect of their understanding
Process
Tutorial questions were rewritten such that they required the students to explicitly construct their knowledge in the following ways:
- Identifying the important concepts
- Establishing the relationships between the concepts
- Confronting common misconceptions
- Relating the concepts to reality
- Developing higher level problem-solving skills
We hoped that students working with these new problems would develop strategies of problem-solving and an understanding of the concepts and their logical connections such that they would be able recognise and apply principles in their appropriate context.
The new approach is illustrated by Examples 1 and 2, an old-style question about Gauss's law and its replacement. Gauss’s law states that the net electric flux emerging from any closed surface is equal to the total charge enclosed by the surface divided by
. It can always be used to find the average electric field over a surface, but its real value is that, in situations with appropriate symmetry, it provides a simple way of finding the electric field at a point.
Example 1 is the way questions were previously put:
Use Gauss's law to find the electric field just outside a conducting surface carrying charge density per unit area
It has been replaced by Example 2:
(a) Describe the Gaussian surface used in lectures to derive the electric field near a flat charged plate. Describe two other Gaussian surfaces which could be used instead. Be careful in specifying their position and orientation.
(b) In response to the question:Use Gauss's law to find the electric field just outside a conducting surface carrying charge density per unit area
the following student answer was given:
Comment on whether this answer is satisfactory, and make any improvements you think necessary. (Pollard, 1994, p.4).
Variations on standard exam questions are also possible. By supplying the algebra and asking students to explain the important steps in the derivation, it is possible to assess the students’ knowledge of the logic of the process rather than their ability to recall a rote response
Evaluation
Student responses to a question of the type shown in Example 2 more clearly indicated the level of Physics understanding at which the students were operating. Even when students do not produce a complete answer to this question the subsequent discussion in tutorials encourages them to examine and appreciate the logic in a way which is rarely encouraged by standard textbook problems (details in Pollard, 1993). A study of students trialling the process in tutorials found that it helped middle range students, comprising the large majority of first year physics students, improve their approach. For very good students, deep learning strategies appeared to already be in place. For students who were struggling and committed to a memorisation and regurgitation strategy the new question type may have even been counterproductive, decreasing the effectiveness of their favoured (or only) learning strategy and thereby increasing their sense of being overwhelmed.
Feedback from tutors in the same study was also positive, indicating that the students were aware of the need to probe concepts, and were willing to do so.
The approach is now further embedded in the curriculum and has been more widely adopted.
Acknowledgement: Alistair Blake's observations of his students' responses provided the original inspiration for this work, and he contributed significantly to the evolution of the project documented here.
References
J Pollard, (1993) Developing physics understanding through guided study, in J. Bain, E Lietzow and R. Ross (eds.) Promoting Teaching in Higher Education, (Griffith University) pp. 355 - 370.
J Pollard, (1994) What are we trying to prove in Physics lectures? presented at the 11th Australian Institute of Physics Congress, Brisbane.
Dr Judith Pollard can be contacted on:
Tel: +61 8 8303 5316
Fax: +61 8 8303 4380
E-mail: judith.pollard@adelaide.edu.au
Adelaide University, Australia 5005
Last updated 2/8/01
