LEARNING AND UNDERSTANDING KEY  CONCEPTS OF ELECTRICITY

Reinders Duit
Institute for Science Education at the University of Kiel, Germany

Christoph von Rhöneck
Pädagogische Hochschule Ludwigsburg, Germany
 

Introduction

This chapter has two major aims: First, to summarize briefly findings on students' pre- and post-instructional conceptions in the domain of electricity and on their double role in teaching and learning processes, namely to be impediments of learning and also to be the necessary building blocks for students' processes of constructing understanding. Second, to employ the case of learning difficulties in electricity to point to more general aspects of the role of students' pre-instructional conceptions in learning physics.

Electricity is one of the basic areas of physics which are important at all levels of physics teaching. At the primary level young children already gain experience with simple electric circuits. At the following levels electricity is systematically taught and is a significant topic in all kinds of schooling. For reasons of a compressed description this review will not focus on the evolution of students' conceptions with age and over the different levels of education. Instead of this, the different conceptions will be listed and described in a loose sequence
 

Students' conceptions of current, voltage and resistance

Everyday meanings of current

Everyday talk about electricity and electrical appliances is markedly different from physics electricity talk; the basic physics terms of electricity, current, voltage and resistance, for instance, are also used in everyday talk, but in significantly different meanings than in physics. As there are certain differences between languages with regard to the meanings given, for instance, the mentioned basic terms of electricity, it is not possible to provide a conclusion that holds across languages. But it is possible to state that the meanings of words for current in European languages generally are nearer to the meaning of energy than to current as used in physics. In other words, the term current in everyday language includes a broad spectrum of meanings with a certain dominance of energy ideas. Misunderstandings in physics classes, therefore, are likely if the teacher is not aware of these differences between his or her way and the students' way to talk about electrical phenomena.

Linear causal effect between batteries and bulbs

For children at the primary school level who have not received any formal instruction it is suggestive to ask them for a circumscription of their concepts of electric processes. But it is possible to analyze how the children handle batteries and bulbs and which explanations they give in relation to their actions as was done by Tiberghien and Delacôte (1976). The result of this study is that children use very general explanations for the functioning of a simple electric circuit. Usually, they establish a causal connection between the battery and the bulb and explain that there is an agent moving between the battery and the bulb. The agent may be called electricity or electric current. Electricity or current is stored in the battery and may "rest" in wires. The agent is consumed in the bulb, i.e., there is no idea of conservation of electricity among these children. The linear causal effect between battery and bulb does not imply a closed circuit. A significant number of children namely think that one wire between battery and bulb suffices and that the second wire to be found in working circuits in everyday life simply serves to bring more current to the bulb. There are also findings that two kinds of current travel both from the battery to the bulb; sometimes they are called "plus" and "minus" current (see below). In the bulb there is a clash of the two currents, a notion which has been called "clashing current" (Osborne, 1983), or there is some sort of (chemical) reaction that leads to the light the bulb provides.

Research has shown that the consumption of current idea does not vanish through formal instruction. This idea and other students' conceptions may be discussed by means of a test which was administered in five European countries to more than 1200 grade 10 students after instruction in secondary schools (Shipstone et al., 1988). The overall result of this test is that despite different school systems and languages -- approximately the same pattern of learning difficulties is found in these countries.

Consumption of current

The conception that current is consumed remains attractive to students even after instruction. Consumption comprises the two aspects of devaluation and diminution of the electric current. In one of the tasks which refer to the consumption idea three statements are presented to students (in connection with a bulb connected to a battery and the bulb is lit up), and they are asked to indicate the statements as true or false. The result was that only a minority of the whole sample agreed to the conservation of current (statement 3):

1: "The bulb uses all of the electric current. "

2: "The bulb uses up a little of the electric current."

3: "All of the electric current. from the battery to the bulb goes back to the battery."

Hence the consumption of current is still attractive since for many students the conservation of current is at variance to the fact that the battery must become "empty ".

In another task (figure 1) the students were asked to compare the readings of several ammeters. The result was that only about 50% of the students gave the correct answer: I = const = 2A.

 
  . FIGURE 1

Local reasoning

Local reasoning describes the fact that students focus their attention upon one point in the circuit and ignore what is happening elsewhere. An example of local reasoning is that many students are regarding the battery as a constant current source and not as a constant voltage source. The battery as a constant current source delivers a constant current, independent of the circuit which is connected to the battery.

 
 FIGURE 2

In the task of figure 2 local reasoning is related to the concept of current. About 60% of the sample hold that I1 = 0.6A, and 12 = 13 = 0.3A. The currents are divided up at every junction point in the circuit in two equal parts. This division is not influenced by what is lying ahead in the circuit. The students argue that "the current does not know in the junction points what happens afterwards in the circuit". The unusual graphical representation of that task makes clear that many students show a tendency to argue on currents only. The current in a single branch is not perceived as a consequence of the voltage across the resistance in that branch.

Voltage in closed circuits
One of the most difficult concepts in basic electricity is the concept of voltage or of potential difference. Before instruction voltage is related to "strength of a battery" or "intensity or force of the current". Even after instruction students use the voltage concept as having approximately the same properties as the current concept. The next task (figure 3) shows the lack of differentiation between the two concepts.

 
 
 FIGURE 3

About 40% of the sample expect the voltage of 6V across all the pairs of points in the circuit and do not differentiate the two concepts voltage and current in the presented situation.

Sequential reasoning

If in a circuit an element such as a resistor is changed, a special kind of reasoning called sequential reasoning becomes manifest. Sequential reasoning means that the students analyze a circuit in terms of "before" and "after" current "passes" that place. A change at the "beginning" of the circuit influences the elements after, whereas the change "at the end" does not influence the elements situated before. The information of change is transmitted by the electric current. The current in a circuit is influenced by a resistor when it comes to this element and transmits this information in the direction of flow and not in the opposite direction.
A task for showing sequential reasoning is presented in figure 4. About one third of the sample shows sequential reasoning, also in similar and more elaborated tasks. Even students at the university level use sequential reasoning in other situations (Closset, 1983).

 
 FIGURE 4
 
 
 
 FIGURE 5
 
 

Resistance

Some difficulties in connection with the concept of resistance may be discussed according to a task with two branches in parallel (figure 5). The influence of changing the resistance R2 on the different currents I1 12, and I turns out to be extremely complicated for most of the students: Only 20% detect that I1 stays the same and the other currents decrease. 12% use an inverse relation between resistor and current and believe that an increase of R2 leads to an increase of 12. 20% consider the source as a constant current source and tick off that 12 decreases, I1 increases and I stays the same. About 10% use sequential reasoning and predict that all the currents stay the same since the resistor R2 is placed "at the end" of that branch and the change of R does not influence the currents "before" the resistors.

The complicated mixture of incorrect argumentation in the last task denotes that instruction generally leads not to a well defined representation of the concepts used in physics. Often, we find even after instruction elements of pre-instructional conceptions loosely connected to some elements of the concepts taught. Beyond that, research has generally shown that students' conceptions are context specific, i.e., they depend on the concrete task which is presented. If the situation changes from a first exercise to a similar (from the physicist's point of view) exercise, and students' may employ substantial different conceptions to solve the task.

Conceptions may overrun empirical evidences -- on the confirmation bias

It is a well known general finding of research on students' conceptions that the conceptions students hold very much influence what they actually see in experiments. Further, students usually are not "willing" to change their conceptions if their prediction is challenged in just one experiment (Chinn & Brewer, 1993).

 
 
 FIGURE 6

Schlichting (1991) provided a striking example of how students do not see what actually is to be seen but what their conceptions allow them to see, so to speak. He presented the experimental setup shown in Figure 6 to a grade 10 class and asked where the thin wire starts glowing when the circuit is closed. There were three different predictions. (1) The wire will glow first at the left or the fight side depending of the assumption of direction of current flow taken as current enters the wire there. (2) The wire will glow up First in the middle as two kinds of current (see above) will come together in the middle. (3) The wire will simultaneously glow up at all places (the correct view). After the prediction the experiment was carried out. Almost everybody saw what he or she expected.
 
 

As mentioned above many students hold the view that current is consumed in a bulb so that less current is flowing back (according to students' views) to the battery. Gauld (1989) challenged that conception by the experiments shown in figure 7. After a quite difficult and painstaking process he succeeded in convincing his class of about 14 year old students that the same deflections of the ammeters may be best explained by the physics view of current conservation. Three months later he interviewed his students on their conceptions of current flow. Most of them did not use the physics conceptions they obviously had achieved in instruction any more. Asked for the readings of the meters a number of them said that they were different, at least a little, although they all had seen and had agreed upon that the deflections are equal three months before.

 
 
 FIGURE 7

Students' learning processes

Many studies like the above summarized European survey on students' conceptions of electricity (Shipstone et al., 1988) have shown that success of physics instruction on achieving the physics point of view usually is limited (see the list of around 280 studies on learning electricity in Pfundt & Duit, 1994). Most studies draw on data after instruction or on comparing data before and after instruction. But there are also some learning process studies available that allow to follow the details of learning processes of individual learners (see the contributions in Duit, Goldberg, & Niedderer, 1992; for a learning process study in the field of electricity see Schwedes & Schmidt, 1992, in that volume). It becomes obvious in such learning process studies that the learning pathways students follow are very complicated: There are forward and backward movements, there are parallel developments and there are dead end streets also. Usually a development towards the science view becomes visible only after a long time, conceptual development towards the physics view, e.g., of electricity, is a strenuous long lasting process. The studies also reveal that there are often developments that go just in the opposite directions than intended by the teacher.

In a study by Niedderer and Goldberg (1995), for instance, a group of three college students approaching the physics ideas of the above discussed simple electric circuit in a kind of guided inquiry approach was involved. These students first had many difficulties to connect a bulb to a battery in the correct way. It took them around 30 minutes to solve that task. The intention of the teacher was to provide students with concrete experiences to allow them to establish ideas about the electric circuit. The students developed a conception well know from other studies and presented above. They viewed current as a kind of fuel that flows from the battery to the bulb and is consumed there. They referred also to previous knowledge taught in science class on positive and negative charge. They merged these two conceptions (the consumption idea and the notion of plus and minus current) in such a way that they achieved a framework that provided fruitful explanations to them. The teacher initially supported their view and did not become aware that the students' ideas developed in a direction he had not intended and that actually hampered further development towards the physics view. These students were unwilling and unable to change their view which had proven very fruitful and plausible for them. In other words, the guidance and support given by the teacher led them to a conception that happened to be a more serious impediment for further learning than their initial everyday ideas.

Teaching electricity taking students' learning difficulties into account

Of course, research in the field of learning electricity has not been restricted to bringing learning difficulties to light but also to address these difficulties in order to improve teaching and learning. A substantial number or studies have been carried out in which new learning and teaching approaches have been evaluated. It is not possible to provide a comprehensive review of the approaches here. Only some remarks on general findings may be given (see the list of referring studies in Pfundt & Duit, 1994).

Conceptual change

Learning in the research domain under review here generally is seen as an active construction process on the side of the learner on the basis of the already existing knowledge. What the learner already knows has proven the key factor in learning of whatever domain. The sketched view of learning is usually called "constructivist" (Tobin, 1993) denoting that knowledge acquisition is a construction process of the individual within a certain social setting. The term "conceptual change" which is widely used and often stands for constructivist ideas of learning in general denotes that learning science usually involves fundamental restructuring of the already existing, pre-instructional knowledge (Vosniadou, 1994). In other words, the term stands for the fact that usually students pre-instructional, everyday ideas about science phenomena are in stark contrast to the science concepts and principles to be learned.

The term conceptual change is not well chosen as it may be misunderstood. Change does not stand for exchange (or even extinction) of the pre-instructional conceptions for the physics concepts. Research has shown that this is not possible and it has also proven that this is not desirable. As outlined above students usually learn at best a kind of hybrid idea that merges facets of pre-instructional conceptions and physics views. Further, many students' pre-instructional conceptions have proven powerful frameworks in daily life context. This is true, for instance, for the conceptions of electricity presented above. In most daily life concerns they provide sufficient guidance to deal with electrical appliances and they allow fruitful everyday discourse about most electrical issues. The view of exchanging students' pre-instructional everyday conceptions therefore has to be exchanged by a context dependency view: A certain coexistence of both views has to be tolerated; students have to learn in physics classes that the physics view provides more powerful frameworks in certain situations and contexts.

Conceptual change and conceptual change supporting conditions

Conceptual change in the above sense, i.e., in terms of students' learning pathways from certain issues of their pre-instructional conceptions towards the physics concepts has proven to include rational (logical) as well as emotional issues. There are many cases known from the literature that students understand the physics view but do not believe it (Jung, 1993). Conceptual change, therefore, has to be embedded into conditions that support the development of students' ideas. Among these supporting conditions are a classroom climate that allows students to voice their ideas and to exchange their views with other students, and where students' ideas generally are taken as serious attempts to make sense of a certain phenomenon by the teacher. Also students interests and motivation play a key role.

In a study on teaching and learning the basic concepts of electricity (Grob et al., 1994) the significance of the mentioned factors became evident. Girls and boys use a different access to learning physics. The girls tend to distance themselves from physics because their interest is low. This does not mean that they do not learn physics. In the female group of those students who show a steady learning behavior intrinsic motivation is a determinant factor for learning physics. Intrinsic motivation is not subject matter dependent and indicates that these students are generally bright students. The boys find an emotional access to physics via interest and they prove to be good and continuous learners as long as their effort depends on interest.

Discontinuous and continuous learning pathways

Students' pre-instructional conceptions of the electric circuit are undoubtedly in stark contrast to the referring physics concepts. In many new teaching and learning strategies available in the literature instruction starts with elicitation of students' ideas and with establishing their experiences with the phenomena in question. As is the case in the constructivist teaching scheme of the CLIS (Children's Learning in Science) project (Driver, 1989), but in many other approaches also, students carry out experiments (for instance, with batteries and bulbs), and develop and exchange their views of the phenomena investigated. From such a basis the teacher tries to guide students towards the physics view in a step by step procedure. Challenging students' ideas is a crucial part in this period, in other words, cognitive conflicts play a major role. Gauld's (1988) strategy briefly discussed above may be taken as a paradigmatic example. Afterwards the physics view is applied to a number of novel situations. Much emphasis also is given students' reflection of their own learning process in order to make students aware in which way their initial everyday ideas are different from the new physics views. These strategies may be called discontinuous as they deliberately draw on cognitive conflicts.

Cognitive conflict strategies, though generally superior more traditionally oriented approaches (Guzetti & Glass, 1993), bear a number of difficulties. The most important is that it is often difficult to make the students see the conflict. Also it may happen that elicitation and long discussion of students' pre-instructional view may strengthen just this view. Therefore, there is the search for strategies that avoid cognitive conflict, i.e., that start from facets of students pre-instructional conceptions that share at least some basic issues with the physics view already, and from this kernel of conformity proceed towards the physics view via a basically continuous pathway. One kind of such strategies may be called "reinterpretation" (Jung, 1986). Grayson (1996) provides the following example for this strategy (her term is "concept substitution"). Instead of challenging students' view of current consumption as sketched above she provides the following reinterpretation: The view that something is consumed is not wrong at all -- if seen in terms of energy. Energy actually is flowing from the battery to the bulb while current is flowing and is "consumed", i.e., transformed into heat and light.

There are other possibilities of continuous pathways towards the physics view of electric concepts. In these cases instruction initially bypasses students' pre-instructional conceptions of the electric circuit and starts with certain more general schemes or with drawing analogies to domains already familiar to students. The most popular strategy of this kind is to draw on analogies to water circuits of manifold kinds. The problem of this standard analogy of physics instruction is that it may lead to severe misunderstandings if not handled with care. Research namely has shown that students hold basically the same conceptions (which have to be termed wrong from the physics point of view) in both the electric circuit and the water circuit (see Schwedes, 1996, for an approach that addresses these problems).

Student oriented structure of science content

Of course, in all new conceptual change approaches for teaching and learning electricity there are attempts to change the structure of physics content in such a way that the learning difficulties revealed in the many studies available may be adequately addressed. There appear to be three key concerns:

(1) Current flow and energy flow have to be clearly differentiated from the very beginning in order to address students' idea of current consumption which has proven to withstand instruction in a very serious way.

(2) Current and voltage have to be differentiated from an early stage on in order to provide students with a view of the phenomenon of current flow that includes the idea of a flow of something in a circuit and the idea of a driving "force" of that flow but that also allows to distinguish these issues.

(3) In order to address the above discussed "local" and "sequential" reasoning dominating students' views of current flow it is necessary to guide students to a "system view" of the electric circuit (Härtel, 1985) , from an early stage on. Whenever there is a change of some sort in one point of the circuit there are simultaneously changes in other points also. An adequate model would not draw on individually moving charges (or particles) but on a view where all particles are intimately interconnected.

Concluding remarks

The domain of electricity is the field where most research on students' learning difficulties is available. Results of this large body of research clearly show that students' pre-instructional conceptions deeply influence or even determine learning. Most of students conceptions have proven impediments of learning as they are in stark contrast to the physics concepts to be learned.

As students pre-instructional knowledge necessarily has to be the starting point of every learning process the impediments have to be overcome in certain intelligent ways. Also here research has provided valuable approaches tat may lead to more efficient and more pleasing physics teaching and learning for teachers and students alike in the domain of electricity and beyond. Much has been done so far, many valuable ideas are available, yet much more still has to be done.

References

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Section C2, Learning and understanding key concepts of electricity  from: Connecting Research in Physics Education with Teacher Education
An I.C.P.E. Book © International Commission on Physics Education 1997,1998
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