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An electric circuit An electric current (I) is mostly the flow of electrons (negatively charged particles) through a material and thus a transfer of electric charge. These negatively charged particles can only move in an electric field, which creates a difference in potential between two points (from a point of high potential energy to one of low potential) if a continuous path is provided for them. The path is called an electric circuit which basically consists of a source a load a switch a transmission system Such a simple electric circuit can be seen in Figure 1 below: battery current (flow of electrons) switch In order to make electrons move, a force must be applied to them. This is known as the electromotive force (e.m.f.) or potential difference. Typical sources of emf are cells, batteries and generators. A load commonly converts the electrical energy from the source into some other forms of energy. For instance, a lamp changes electrical energy into light and heat, or an electric motor changes electrical energy into mechanical energy. So a load can be any electrical device. A continuous path for the electrons to move is usually a loop of insulated copper wire, because copper is a good conductor. A switch is a component that breaks and closes the flow of current. For instance, when you turn on a switch, it closes a gap in the circuit with a strip of conducting material, allowing the current to flow. When the switch is turned off, the gap is opened again. This breaks the circuit and stops the flow of current, because the air that fills the gap is an insulator. In Fig.1 we have seen that depicting the various components in an electric circuit gets more confusing and more complicated the more elements we have in a circuit. To simplify the representation of the circuit, fixed graphical symbols are used. Figure 2 below shows a few examples of symbol standardisation. Wire Connection between wires Battery Light bulb Switch List of words: electric current – elektrischer Strom charge – die Ladung thus – folglich particles – Teilchen elctric field – elektrische Feld to create – schaffen, bilden, herstellen potential difference – Potenzialdifferenz continuous – dauerhaft to provide – bereit stellen electric circuit – Stromkreis path – Pfad, Weg source – die Quelle load – der Verbraucher transmission system – Übertragungssystem wire – der Draht switch – der Schalter force – die Kraft to apply – anlegen electromotive force – elektromotorische Kraft cell – nicht wiederaufladbare Batterie to convert – umwandeln mechanical energy – mechanische Energie device – Gerät, Vorrichtung loop – Schleife insulated – isoliert copper – Kupfer conductor – Leiter component – Bauelement, Bestandteil to break – unterbrechen gap – die Lücke, der Freiraum a strip – ein Streifen insulator – Isolator depict – darstellen various – verschiedenartig to simplify – vereinfachen standardisation - Normung Activities: I)Answer the following questions on the basis of the impulse text. 1)How is electric current defined? 2)What are electrons? 3)What does emf stand for and what is it needed for? 4)Where do electrons move? 5)What different parts does an electric circuit consist of? 6)What is the function of each component in an electric circuit? Give an example each! II)On the basis of Figure 1 draw a simple circuit by using the standard symbols, which are represented in Figure 2. III)Hands-on activity a)Build a simple electric circuit with the materials/components given. b)Write down the instructions! c)Present your circuit board! IV)Match the words on the left with the definitions on the right! (could even be done as a crossword on the basis of HotPotatoes) electric current – charge – particles – an electric field – continuous – to provide – an electric circuit – a source – a load – a battery – to convert – transmission system – device – to insulate – copper – conductor – component – to break – a gap – insulator – a material where electrons can easily flow it is a path where electricity goes through any space; nothing in between it can be re-charged, an accumulator to open, to turn off to cover wires the flow of electrons property of electrons and protons connecting wires permanent to supply a material where electrons can hardly flow an ………… …………. is caused by charged particles conducting metal it converts one form of energy into another one very small parts emf is provided by a ………….. to change into another state an essential part of an electric circuit a load can be any electrical ……………… Sources: Electricity Usborne Publishing Ltd, 1991, ISBN 0860200787 Science and Technology Oxford University Press ISBN 0199101434