Using circuit and wiring Diagrams to identify students' mental models of basic electric circuits
2. Research design
The main focus of this study was to find out the extent and nature of the common errors students made in drawing both circuit as well as wiring diagrams. In order to do this, all the drawings made in two tasks and the final examination from a cohort of students were recorded, categorised and analysed.
Who are the students?
The students selected for the study were registered for a Design and Technology module as part of a Bachelor of Education degree at a South African University. This module was a single semester module used to prepare students to teach basic
electricity to primary school pupils. The module was project based and the project used was the construction and wiring of a model doll's house, irutially used as a context to learn electricity and to see the effect of context on performance in the tasks of drawing circuit and wiring diagrams. Context was integrated into the design of the
Figure 7.1.
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Do,;-,:. bv1h 1 ight uc,> ...• YU, / NO A,e,,\.,or,. , ....
Sample test items for the diagnostic phase.
course as a way to improve students' attitudes as well as levels of self-efficacy (Bandura, 1994). Since 61 % of the class was female, the wiring of a house was a context that was chosen to be appealing to female students. The sample size was 1 14, 70 of whom were female and 44 of whom were male. Of these students, 33% (38) had been scholars at educationally disadvantaged schools, while 67% (76) had been scholars at educationally advantaged schools. The distinction in this instance between an advantaged school and a disadvantaged school was made using a government approved data base and ranking system which is determined by the relative wealth of the school itself (Education Management Information Systems, 2006). The
differential education provided under apartheid has resulted in differences in school performance, particularly in mathematics and science, where those students who went to educationally disadvantaged schools perform worse in science and mathematics related disciplines than do those who went to educationally advantaged schools (Perry
& Fleisch, 2006). Typically, the class was made up of students who had had little scientific education at school (72%; 82) compared with those who had taken Physical Science to school exit level (28%; 32).
Programme of instruction and rationale for the tasks given
The programme of instruction was based on conceptual change strategies pioneered by Osborne and Wittrock (1983), Posner, Strike, Hewson and Gertzog (1982) and later developed by Kyle, Abel and Shymansky (1989). Into this were also integrated ideas of Socratic dialogue, particularly when it came to developing opportunities for cognitive conflict. An initial diagnostic phase that required students to predict
whether or not a bulb would light up was designed to elicit preconceived ideas about circuits and the nature of current. Examples of test items are shown in figure 7.1. In order to ensure that the diagrams were understood properly, the light bulb
construction was made explicit in a diagram in the students notes (see for example Shipstone, 1988; Stanton, 1990b). During the diagnostic phase of the Programme, students were asked to predict whether a bulb would light up or not (see sample questions in figure 7.1). Of the cohort, 44% appeared to use unipolar thinking in making these predictions.
The diagnostic phase was followed by a problem solving phase where students were required to design and make a number of circuits using standard equipment. The focus of this phase was the development of an understanding of fundamental electrical concepts such as current, voltage, energy, power and charge through a non- mathematical set of activities. In this phase, students were expected to design, construct and interpret wiring as well as circuit diagrams.
The challenge phase of the programme moved from circuit design and construction to designing wiring diagrams. Several tasks were given, two of which form part of the data collected in this study, namely, the design. of a circuit and wiring diagram for a simple three roomed house and the design of a circuit and wiring diagram for a car. It must be noted that the intended circuit for the car was electrically identical to the intended circuit for the house.
Finally, in the application phase of the programme, students were required to design both circuit and wiring diagrams for a house of their own design and manufacture and then wire it according to these diagrams, producing in the end a finished product, a working electrified dolls house.
3. Results
A total of 246 errors were recorded in two different contexts (the wiring and circuit diagrams for a house, the wiring and circuit diagrams for a model car) as wel1 as in the examination script. Errors were categorised according to similarity and any
evidence of models of electric current as identified in Table 7. I above. These categories are outlined below, grouped according to type as shown in Table 7.2 below.
Error categories in the drawings
Figure 7.2. Unipolar wiring diagram (house).
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Figure 7.3. Examples of Short Circuits used in designing circuit diagrams.
Error A: (41/246) Figure 7.2 shows students drawing the correct parallel circuit diagram, but a wiring diagram that is unipolar.
Error B: (11/246) Drawing the circuit diagram when asked to draw the wiring diagram. Students confuse the circuit and the wiring diagrams, or simply do not understand the difference. Mostly the circuit diagrams drawn were correct.
Error C: (36/246) Figure 7.3 shows short circuit wires present in the Circuit Diagrams.
Error 0: (28/246) Figure 7.4 shows components "left hanging" in the wiring diagrams.
Error E: (24/246) Short circuit wires in the wiring diagram. Similar to error C, the only difference is that the short circuits are shown in the wiring diagrams.
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Figure 7.4. Error D: Components left hanging.
Error F: (6/246) Figure 7.5 shows the main switch is drawn in parallel with the battery. In this error, students drew a switch across the terminals of the power source, effectively causing a short circuit. This actually does work in that when the power source is shorted, everything is switched off. It is however, a poor design from a technological point of view in that the battery will run flat, or the power source over heat and/ or a fuse will blow.
Error G: (I 2/246) Spatial visualisation problems when drawing the wiring diagram. Students who showed this error drew the wiring diagram simply as a set of wires that followed the shape of the house plan. This was taken to mean no
understanding of what was happening in the circuit, apart from the fact that the circuit does need to be integrated into the plan of the house.
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_,,Figure 7.5: Battery is short circuited by a switch.
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Figure 7.6. Example of the correct parallel circuit design and the corresponding series circuit wiring diagram from the same student.
Error H: (36/246) Figure 7 .6 shows the drawing of a simple series circuit as the wiring diagram, while drawing the correct parallel circuit for the circuit diagram.
Error I: (7/246) The student draws the wiring diagram when asked to draw the circuit diagram. This is much like error B, where the circuit diagram is drawn in place of the wiring diagram. This could be that the student is confused about the question.
Error J: (3/246) Wiring diagram more accw-ate than circuit diagram. In some cases, the students drawing of the wiring diagram for the house contained fewer errors than the drawing for the circuit diagram.
Error K: (14/246) Non-functional loops in the circuit.
Error M: (1/246) More than required connections to lamp/ component. In these cases, components were drawn with more than the number of connecting points they actually had.
Error P: (14/246) description.
Error S: (2/246)
Diagrams drawn with no batteries, cells or power of any
Switches for parallel circuit wrongly placed. On two occasions, the switches for each light in a parallel circuit were wrongly placed.
In order to determine common ways of thinking, errors were organised into groups that were similar or that were related to common alternative conceptions identified in the literature. These are shown in Table 7.2.
Table 7.2: Groupings of common error according to Error type
Context House,
Error Common House Car Exam Car& Description of Common Error Group Error (% of (% of (% of Exam Group
Label total) total) total) Combined Type
Unipolar thinking used when
I A 33 9 8 17 drawing the wiring diagram but
not in the circuit diagram Type If
Components "left hanging" in the
D&K 4 27 22 17 Wiring Diagram, non-functional
loops in the circuit Type IIJ
Simple series connection
H 6 24 16 15 portrayed as Wiring Diagram
after a correct parallel circuit diagram has been designed Type IV
Short circuit wires present in C, E&F 43 2 31 27 either the Circuit Diagram or the
Wiring Diagram Other
P,G,B,J,
J,S,M,Y 15 40 23 25
Total% 100 100 100 100
(Actual Number) (82) (68) (96) (246)
X 13 26 8 47 Did not complete
Frequency of common errors
The frequency of common errors recorded in the diagrams is shown in the graph in figure 7.7 below. This graph compares the actual number of errors made in each of the two contexts as well as the examination. The pattern presented here shows a sluft from a large number of errors of category A in the house task to a fewer number in the car task and the examination. However, one can also see a simultaneous rise in
:frequency of errors such as C, D and H, which might be an indication of students' ability to transfer concepts from one context to another.
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A B C D E F GH J K L MP SY X Modelused
Figure 7. 7. Frequency of errors in drawing circuit and wiring diagrams
Types of error
Four dominant types of error emerged from the analysis of the diagrams (Table 7.2).
These types of error are described below. The largest single factor in circuit errors is the use of unipolar thinking in designing wiring diagrams. This amounted to 83/246;
(34% of the total), which is shown in both type I and type Il errors.
Type I errors
The simultaneous representation of unipolar and non-unipolar thinking in the circuit and wiring diagram design accounted for 17% of all the errors made in the three contexts. (Error A: 41./ 246)
Type If errors
In Errors D and K, which showed combined unipolar and completed circuit models (42/246, 17%), students appeared to accommodate elements of unipolar thinking into the design of completed circuits. This is shown in Figure 7.4, where the idea of a closed loop dominated the design of the circuit and components are connected to the loop in a unipolar way.
Type Ill errors
Figure 7.6 shows the simultaneous use of series and parallel circuits to represent the same physical circuit, which made up 15% (36/246) of all the errors.
Type IV errors - short circuits
The drawing of short circuits in multiple ways and contexts was in fact the largest single error recorded. (66/246, 27%) The errors C and E both showed short circuits drawn by the students.