Before starting the activities of Direct Circuit Electricity unit students should have prior knowledge of:

• Some electrostatics: the matter consists of two kinds of electric charge and that at least some negative charge can be moved from one object to another leaving the first positively charged and the second negatively charged. Once the charges stopped moving we explore the electrostatic forces between them (Coulomb´s law), the concept of potential difference (voltage).
• Phenomenon of electric current, the physical quantity of electric current.
• The schematic symbols for basic circuit elements. A circuit sketch.
• The set of designed activities do not cover all the topics concerning direct electric circuit. The activities presented here were selected and designed with regard to their potential towards IBSE and they do not to cover the entire topic of direct electric current. Nevertheless, there are some concepts that are needed within the activities (like power, energy delivered to the circuit, electromotive force) and hence they should be introduced before the activity starts within a theoretical lesson.

In the unit students are introduced to the following scientific concepts and ideas:

• In order to have stable electric current we need a closed electric circuit with certain elements.
• There are materials that conduct electric current. They can differ according to their ability to conduct electric current.
• The amount of electric current can be measured by ammeter, voltage can be measured by a voltmeter, how to connect ammeter and voltmeter into the circuit. We can use ICT tools (current and voltage) sensors for measurement. Electric current is the same at all places of the simple circuit.
• The concept of resistance and Ohm´s law. There are many elements that can be a part of the circuit. They can behave differently when connected in a direct electric circuit.
• The resistance depends on temperature. This relationship can be increasing (metal conductors) and decreasing (semiconductors). This relationship can be used for designing a thermometer.
• Theoretical model of electric circuit based on the concept of surface charges. Resistors in series and parallel.
• Electricity and human body. Ohm´s Law for a human body.
• The concept of power and energy delivered to the circuit. These concepts basic introduction is not a part of the activities. Their introduction must be done within a lesson before the activity 9 (Intriguing behaviour of bulbs). Electric current delivers energy (power) to the circuit (e.g. to the bulb). The energy delivered determines the bulb brightness.
• The concept of electrochemical cell (primary and secondary) and a battery made of a connection of several cells.
• The concept of terminal voltage (compared to the electromotive force) and its dependence on the current flowing through the circuit. The concept of internal resistance.
• Power transferred from the battery to the load. Power transfer efficiency. Theoretical model of the battery behaviour.
• Batteries connected in series and parallel. Emf and internal resistance of these batteries.
• The properties of battery. Battery capacity. Energy supplied by the battery. Other important parameters.
• Everyday use of batteries. Environmental aspects of battery disposal.
• Alternative electric sources (fuel cell, photovoltaic cell)

The detailed explanation of the model of electric circuit can be found in the articles:
Haertl, H.: The electric Circuit as a System: A New Approach, Eur.J.Sci.Educ., 1982, vol.4, No.1, 45-55
Sherwood, B., A., Chabay, R., W. A unified treatment of electrostatics and circuits, available at <http://matterandinteractions.org/Content/Articles/circuit.pdf>