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MODELS OF ELECTRICITY Scientists used models to help them understand a process. Each part of the model represents something in real life. A good model fits with the facts. You are going to compare the ‘coal truck model’ and the ‘supermarket’ model of electricity and decide which one you think is best. Facts about electricity Electricity carries energy to make things work. This flow of energy is called an electric current. You need a complete circuit to transfer energy from a battery to make a lamp light. The current is the same on both sides of the lamp. There is a voltage (change in energy) across any part of a circuit where energy is entering or where energy is exiting the circuit. The coal truck model This model shows a coal mine and a power station. There is a single-track railway between the mine and the power station. Coal trucks run along the railway. The coal trucks can move quickly or slowly along the track. At the coal mine, the coal trucks are filled with coal. The coal trucks run along the tracks and deliver the coal to the power station. The empty coal trucks then return to the coal mine to be filled with coal again. -22- Read the description of the ‘coal truck’ model carefully and study the diagram. Then answer the following questions: 1. In the ‘coal truck’ model, what represents: (i) the circuit? ___________________ (ii) the battery? ___________________ (iii) the lamp? ___________________ (iv) the energy? ___________________ 2. The moving trucks represent the current. When the truck speeds up, does the current increase or decrease? _______________________________________________________________ 3. Do you think there is anything in the model about voltage? Explain your answer. _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ Extension task 4. Do you think this is a good model? Explain your answer. _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ -23- The supermarket model Imagine that a new supermarket has just opened and it is so busy that a special system of delivering bread from the nearby bakery has been set up with a chain of delivery vans. Complete the ‘cut and stick’ exercise and then fill in the blanks on the passage about the ‘supermarket’ model. -24- Supermarkets and electric circuits 1. The bakery is like the _______________ in the circuit. 2. The vans are like the _______________ in the circuit. 3. The bread the vans are carrying is like the _______________ carried by the _______________ in the wire. 4. The supermarket is like the _______________. Here the bread is passed onto the customers just like the _______________ carried by the charge is transferred to _______________ energy and _______________ energy in the bulb. 5. The empty vans return to the bakery for more bread. This is the same as the _______________ going back to the _______________ for more _______________. 6. If the bakery manager speeds up the vans leaving the bakery, bread arrives quicker at the supermarket. This is like _______________ arriving more quickly at the _______________ in the circuit. 7. If the bakery manager loads more bread onto each van, then more bread is delivered to the supermarket in a certain time. This is like more _______________ being delivered to the _______________ in a certain time in the circuit. 8. The chain of moving vans is like a flow of _______________. In a circuit we call this an _______________ _______________. -25- Electric circuit model Study the diagram of the ‘electric circuit’ model below and then with your partner, compare it to both the ‘coal truck’ model and the ‘supermarket’ model. Which was the better model for you, the ‘coal truck’ model or the ‘supermarket’ model? Explain your answer. -26-