Learning Aims: To deepen and widen students’ knowledge about the simple electric circuit. Materials: Black boxes with four connectors (that are mutually interconnected in different ways inside each box using wires or resistors), bulbs, batteries (or some other convenient source of DC voltage), leads. Suggestions for use: We divide the class into groups of three. Each group has all the necessary equipment ready on their table. We hand them out the Black box’s secret worksheet and let the students perform their own experiments in a guided discovery/inquiry way. At the beginning they should answer introductory questions that should update their knowledge necessary for independent investigation. In accordance with the principles of inquiry based learning students first draw possible ways of interconnection, then they propose a procedure for investigation and, finally, they perform an experiment to reveal the internal structure of the boxes. They use a power source, wires and a bulb to indicate the current (yes or not, strong or less strong) through a selected path. During the independent investigation the teacher observes and by asking questions moderates the individual work of the students. (In case of a less advanced class, the questions are answered one by one and the correctness of the answers of different groups is checked in the form of a class-wide discussion). After the experiments are finished, the contents of the black boxes are revealed – the students check the correctness of their investigations and in case they have made a mistake they try to analyze the cause of the mistake. Possible Questions: What internal connection corresponds to the situation when the bulb lights up? What internal connection corresponds to the situation when the bulb lights up but it shines dimmer than in the previous case? When is the brightness of a bulb connected in an electric circuit lower and when higher? What internal connection corresponds to the situation when the bulb does not shine at all? What is understood by the term “black box”? Where can we find black boxes in everyday life?