Learning Aims: Understanding the conduction mechanism in metals in terms of the electrons´ motion Understanding the concept of surface charges on conductors Understanding the role of resistor in a current carrying circuit Understanding that the current is divided at the junction Understanding what is the final resistance of two resistors connected in series (parallel) Materials: • Animations available at http://www.astrophysik.uni-kiel.de/~hhaertel/CLOC_doc/CLOC_doc_uk/index.htm Suggestions for use: This activity is aimed at conceptual understanding of electric circuit through the concept of surface charges. The explanation can be found in Haertl, H.: The electric Circuit as a System: A New Approach, Eur.J.Sci.Educ., 1982, vol.4, No.1, 45-55 Haertl, H.:Conceptual learning of Circuit, available at http://www.astrophysik.uni-kiel.de/~hhaertel/CLOC_doc/CLOC_doc_uk/index.htm Sherwood, B., A., Chabay, R., W. A unified treatment of electrostatics and circuits, available at http://matterandinteractions.org/Content/Articles/circuit.pdf. The activity should be guided by the teacher who carries out an interactive discussion in order to explain the basic mechanism of electric current in a circuit and the related concepts. Within the interactive discussion teacher ask questions and students try to formulate answers. The important point is not to give the answer but try to make students think to come to the answer by themselves. Therefore the questions are formulated to revise the already known facts towards new situations and coherence. Here is a possible scenario how to carry out the activity with the questions and corresponding answers. The first set of questions is aimed at the revision of the already known facts. Possible Questions: When is the object electric? What is an electric power source? How does electric current flow through a conductor? How does electric current flow through a resistor? Why is the voltage on the current-carrying resistor? When do electrons pull together (resistors in series)? How is the current divided in a junction? What is the resistance of two resistors connected in series (parallel)?