Research in Engineering Education Symposium 2011 - rees2009

Universidad Politécnica de Madrid (UPM) Página 47 de 957
was to check whether students were able to apply Kirchhoff’s current and voltage laws in
the presence of some irrelevant and possibly confusing information. For a correct answer,
the students simply needed to infer IA = IB = 0.3 A from KCL, and UA = 0.5 UC from KVL and
the fact that bulbs A and B are identical. While our main interest was how well students
would do on task (c), we wanted to know the number of students who answered the
previous two tasks correctly as a baseline for interpreting this result. For task (c), students
needed to check the validity of the inference from the given data for each statement
separately. In order to do so for statement X, they needed to recognize that data for a
single load (i.e. a single point on the load line) was not sufficient to conclude whether the
battery could be considered an ideal source or not. As for statement Y, however, a
comparison of the resistances (i.e. the ratios of voltage to current) for bulb A (or B) and
bulb C was possible and yielded different outcomes (0.5 UC/ 0.3 A versus UC/0.5 A),
thereby allowing the conclusion that statement Y was indeed correct.
Figure 2: Circuit diagram in quiz question on applicability of model assumptions
All three tasks were given in multiple-choice format with an (open-ended) request to
explain the reasoning used. In task (a) the distracters were 0.2 A (i.e. IC – IB) and 0.5 A (i.e.
IC), as well as the range between these values (but ≠ 0.3 A) and the statement that an
answer was not possible. In task (b) the distracters were “less than 0.5 UC”, “between 0.5
UC and UC”, “equal to UC”, and “greater than UC”. In task (c) the four choices were
“statement X”, “statement Y”, “both statements”, or “neither”.
Of the 314 students who participated in the quiz, about 82% correctly determined the
current through bulb A (task (a)). About 50% of the students correctly compared the
voltage across bulb A to that across bulb C (task (b)). Of the students who answered both
these tasks correctly (corresponding to 46% of the total), about a quarter (23%) decided
that only statement Y could be inferred from the data presented. An additional 14% did so
for statements X and Y. Unfortunately, only about a third of the students gave an
explanation for their answers. Very roughly about half of the explanations associated with
the correct answer accounted for the different ratios for voltage and current in a way that
could be interpreted as correct. Most of the others, as well as most of the explanations
associated with incorrect answers, referred to statements X and Y as facts that they had
learned to be generally true or untrue. It may be said that these students misinterpreted
Proceedings of Research in Engineering Education Symposium 2011
Madrid, 4 th - 7 th October 2011