Preliminary Studies on Students' Understanding of Electricity and Magnetism for the Development of a Model Dased Diagnostic Instrument

ness versus their experience. The question we posed was: You have learned that charges of same type repel and that charges of different types attract. All objects in the world are made up of atoms, which consist of positive nuclei and negative electrons. If positive and negative charges attract each other, will the nuclei and electrons collide and land on each other? All students stated that they would not collide. The data suggests that a natural collision of the nuclei and the electrons were considered counter intuitive to begin with. However, after stating so, some would speculate that if they do collide then it would result in a nuclear reaction. The E field of the nuclei keeping the electrons away from it seems to be a common belief. This suggests a lack of understanding of the principles but a possible model a ‘shield’ to prevent collision. Other ideas include electrons repelling each other and driving them far apart from the nucleus and arguing that the atom as a whole is neutral. Classical mechanics was also used, stating that centrifugal force keeps the electrons away. Analogies were also given: Electrons orbiting the nucleus are similar to the moon orbiting the earth. An interesting revelation though is that in a similar analogy, one student states that: “Electrons maintain an orbit just as the gravitational pull of the sun does not pull the earth towards it.” It seems that the student is suppressing the effect of the central force in place of the orbital (tangential) motion. The weakening of the Coulomb force due to the presence of neutrons in the nucleus was also stated. Quantum ideas were explicitly stated only once. Given the question (context) considered, we see how the students respond, sometimes moving across domains (solar system analogies and classical mechanics) and sometimes using day-to-day common knowledge (such as nuclear reactions) and ideas from the same concept settings such as the E fields. We also see that they tend to disregard well-known principles somewhat knowingly to explain another. We note that this type of study yields a collection of ideas