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P1 4.5 – Questions and answers 1 Why is the voltage increased before electricity is sent through the National Grid? A Increasing voltage reduces the current, which reduces the amount of energy wasted as heat. © Pearson Education Ltd 2011. Copying permitted for purchasing institution only. This material is not copyright free. This document may have been altered from the original. P1 4.5 – Questions and answers 2 Why is the voltage then reduced before electricity is supplied to homes? A Lower voltages are safer. © Pearson Education Ltd 2011. Copying permitted for purchasing institution only. This material is not copyright free. This document may have been altered from the original. P1 4.5 – Questions and answers 3 Look at Figure 1. The transformers are labelled A–D. For each transformer, say whether it is a step-up or step-down transformer. A A is a step-up transformer; the others are all step-down transformers. © Pearson Education Ltd 2011. Copying permitted for purchasing institution only. This material is not copyright free. This document may have been altered from the original. P1 4.5 – Questions and answers 4 Which of these electricity supplies provides the most power: 2 A at 230 V or 18 A at 20 V? Explain your answer. A 2 A at 230 V (this provides 460 W while 18 A at 20 V provides 360 W). © Pearson Education Ltd 2011. Copying permitted for purchasing institution only. This material is not copyright free. This document may have been altered from the original. P1 4.5 – Questions and answers 5 A step-down transformer halves the voltages of the electricity supplies in question 4. What will the new currents be? A Double the values given: 4 A and 36 A. © Pearson Education Ltd 2011. Copying permitted for purchasing institution only. This material is not copyright free. This document may have been altered from the original. P1 4.5 – Questions and answers 6 An advert for solar cells claims that any electricity that the homeowner does not use can be sold to the National Grid. Explain why this claim is not entirely correct. A If a house is not already connected to the National Grid (because it is in a remote location), it may not be economic to connect it; electricity cannot be sold if there is no connection. © Pearson Education Ltd 2011. Copying permitted for purchasing institution only. This material is not copyright free. This document may have been altered from the original. P1 4.5 – Questions and answers 7 What are the advantages and disadvantages of burying power cables underground? A Advantages: does not cause visual pollution, protected from the weather; disadvantages: more insulation is needed, it is more expensive to install, and it is harder to find faults. © Pearson Education Ltd 2011. Copying permitted for purchasing institution only. This material is not copyright free. This document may have been altered from the original. P1 4.5 – Questions and answers 8 Explain why the following statement is partly correct and partly incorrect: ‘A step-up transformer increases the energy provided by the electricity supply.’ Use data from Figure 1 to support your answer. A A step-up transformer increases the voltage of the supply, and reduces the current. The amount of energy wasted as heat depends on the current, so by increasing the voltage the transformer has reduced wasted energy and so increased the amount of energy that is usable. However, the total energy (including wasted energy) remains the same because the power (energy per second) depends on both current and voltage. © Pearson Education Ltd 2011. Copying permitted for purchasing institution only. This material is not copyright free. This document may have been altered from the original.