LICENCE TO LIGHTING,TEACHER S BOOK

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2 Licence to Lighting Teacher s book Licence to Lighting is a small instructional programme intended for the subject natural and technical science in its first level. By working with elementary teaching in electricity, it is our hope that the pupils will get a basic knowledge of issues such as current path, conductive power, line resistance, series connection and parallel connection, and that they will get an intuitive understanding of the relevant items. The items have not necessarily to be used all of them. Licence to Lighting consists of 8 elementary exercises, which the pupils have to work their way through, before they will obtain the Licence. After having solved the 8 exercises, the pupils can start on the extra exercises, which are part of the programme as well. There are also a few theoretical exercises, which the pupils can solve at home together with their parents. The idea with these home exercises is partly to keep the attention on some important items, partly to inform the parents what their children are working with at school through exercises involving the parents active work, and last but not least, the idea is to open for a dialogue on electricity safety in the homes. The Danish Physics and Chemistry Masters Association has kindly lent us some illustrations from their publication Electricity 7. You can print all the teaching and pupils material in colours from the We thank Inger Wøldike and first class A of Søndermarksskolen at Frederiksberg very much for their help in testing and developing Licence to Lighting. Primary and lower secondary school project Licence to Lighting is the first finished teaching programme from the primary and lower secondary school project, which The Danish Committee for Electrical Training and Education started in August Further information El-Fagets Uddannelsesnævn (The Danish Committee for Electrical Training and Education) Højnæsvej 71 DK-2610 Rødovre Telephone: The project is mentioned at our home page: Project adviser is Mr. Erland Andersen Contact by efu@efu.dk or erland@jyde.dk The Danish Committee for Electrical Training and Education is taking care of the interests of The Danish Electrical Union and the Electrical Contractors Association concerning education, development and teaching material within the electrical trade. 1

3 General comments on Licence to Lighting The idea with this programme is that the pupils - without much instruction - are working their way through the practical exercises and have their exercises looked through by the teacher. When a pupil has obtained his/her Licence to Lighting, he/she may start on the extra exercises, which are generally a little more difficult. The theoretical exercises are supporting what the pupils have worked with in practise. Electricity and safety When working with Licence to Lighting the pupils are only working with batteries and bulbs intended for a very small potential difference. So there are no safety problems and restrictions, as long as they are working with the materials, which are shown in the exercises. However, it will be relevant to make it completely clear to the pupils that they are not to experiment with electricity from a switch, as it can be deadly dangerous. Short about important electricity items Potential difference (voltage) is measured in volts with a voltmeter. If the potential difference is large, the source of energy can easier send current through for instance a wire. Earlier, the potential difference was 220 volts in ordinary switches. Today, the potential difference is changed to 230 volts, and by doing so, we are getting a little more power. The three-phase installations are also changed. Today they are at 400 volts against earlier 380 volts. An ordinary battery is at 1.5 volts. If you put two batteries together in series, the potential difference will be at 3 volts. Three batteries in series will be at 4.5 volts. Current intensity (amperage) is measured in amperes with an ammeter. The electric current in a wire consists of electrons, which are moving from! to +. For historical reasons we are saying that the current is going from + to!. The power is measured in watts with a wattmeter. The bigger power (wattage) an electric device is having, the more current is running through the device. For instance, a boiling plate for 1,000 watts is converting 10 times as much energy per second as a bulb for 100 watts. By multiplying the potential difference by the current intensity, you can find the power. Potential Difference multiplied by Current Intensity = Power Units: (volts) (amperes) = (watts) You can find the energy, which an electric device is converting, by multiplying the power by the time during which the device has been used. Power multiplied by Time = Energy Units: (watts) (hours) = (watt-hours) In practise, watt-hours are too small an entity - instead kilo-watt hours are used, abbreviated kwh, where k stands for kilo, which means 1000, and h stands for hour. We know the word kilo from kilometre = 1000 m and from kg (kilogram) = 1000 g. 2

4 The text on the bulbs, which we have used, is 1.5 volts and 0.09 amperes. The power of the bulbs is 1.5 volts multiplied by 0.09 amperes = 0.35 watts. If the1.5 volt-bulb is put at a higher potential difference - for instance by putting more batteries together in series - the current intensity through the bulb will be higher - more energy will be deposited in the filament of the bulb, and it will burn out. You can measure potential difference as well as current intensity and power directly with measuring instruments, which are used in physics/chemistry. If you will use these measuring instruments, it is a good idea to address the physics/chemistry teacher to get a careful instruction how to use the instruments, so that you can use them correctly. Comments on the individual exercises Licence to Lighting 1 In the first exercise, the pupils have to find out that the bulb is only giving light when the side of the bulb - the screw thread - and the bottom of the bulb are connected to the top (+) of the battery (!). It is important that the circuit is closed - that there is a closed current path - if it is not the case, there will be no current. When the pupils have solved the exercise, you can ask them if the wire has to be held at a specific place of the screw thread, or if it can be placed anywhere on the screw thread. Let a pupil draw the closed current path on the blackboard. Together with the pupils, you can now demonstrate that there will be no current if the current path is not closed. The fact that it is once decided that the current goes from + to!, is without importance at this class level, and therefore not necessary to mention. 3

5 Licence to Lighting 2 In the second exercise, the pupils have to look closer at a bulb. The pupils will see the filament, where the electrical energy is deposited, and they will also have to find out what is written on the bulb. Now, it will be natural to discuss: Potential difference - volts Current intensity - amperes Power - watts The ordinary round batteries used in this programme are at 1.5 volts. In the homes, there are installations for 230 volts and three-phase installations for 400 volts 230 volts as well as 400 volts can be deadly dangerous, so the pupils must under no circumstances work with more than 25 volts alternating current (AC) and 60 volts direct current (DC), and furthermore special regulations are set up regarding the power supply. Licence to Lighting 3 This exercise resembles exercise 1, but in this one the pupils have to put the bottom of the bulb or thread directly on one of the battery poles. The other battery pole is then connected either to bottom or thread with the wire. The closed current path is again indicated at the drawing. 4

6 Licence to Lighting 4 In this exercise, the pupils learn how to use a battery holder and a socket for practical reasons. The wires can be fixed so neither bulb nor battery are rolling away. The closed current path is again indicated at the drawing, this time also through the battery holder (?) and the socket. Licence to Lighting 5 and 6 In exercise 5 the pupils have to make a series connection with 2 bulbs - either both bulbs are giving light or both bulbs are out. In a series connection the bulbs CANNOT be turned on independently. It is not necessary at all at this class level to mention technical terms such as series and parallel connections. In exercise 6 the pupils have to make a parallel connection with 2 bulbs - the bulbs can be turned on and off independently. Therefore, the pupils are not allowed to put two wires end to end in this exercise. Series connection In series connections, the bulbs are either all on or all off. Think of many Christmas tree chains. 5

7 Parallel connection In parallel connections, you can turn all the bulbs on and off independently Think of ordinary house installations Licence to Lighting 7 When the pupils have put together the instruments, let them then control if the bulbs are giving light. Some materials are good conductors, others are bad conductors, and some cannot conduct the electric current at all. Those materials, which cannot conduct the current, are called insulators or non-conductors. Generally, metals are good conductors, and therefore they are used in wires, which are normally made of copper with plastic around. Plastic is a very bad conductor - an insulator. The exercise distinguishes between 3 results: The bulb gives normal light The bulb gives dim light The bulb does not give light at all 1. When a good conductor is put in between the alligator clips, the bulb is giving normal light 2. In some cases, you will see the filament light dimly. A little current is passing through the filament but not enough to make the bulb give normal light. The material which is put in between the clip is able to conduct the current but is neither a good conductor nor an insulator (non-conductor). 3. When the bulb does not give light at all, or the filament does not glow, the pupils have put an insulator (non-conductor) into the circuit. If the pupils have put an ordinary pencil into the circuit, it is possible that the bulb is giving normal light, and also that it does not give light. Wood is an insulator, so if the alligator clips are touching the wood, the bulb will not give light. What we write with is black lead, and black lead is able to conduct the current. If you have dropped the pencil on the floor, the black lead inside the pencil may be broken, and then it cannot conduct the current. 6

8 Licence to Lighting 8 This exercise is meant to remind the pupils of the closed current path - if the current path is not closed, there will be no current, and the bulb will not give light. 7

9 Home exercise 1 (answer) Find a bulb for 230 volts. Write at the drawing what is written on the bulb. Draw the wires which you think are inside the bulb 8

10 Home exercise 2 (answer) Look at the bulbs. 2 of the bulbs are giving light. Are you able to find these 2 bulbs? 9

11 Conversation Sheet 1 10

12 Conversation Sheet 2 11

13 Conversation Sheet 3 12

14 Conversation Sheet 4 13

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16 List of materials 15