1. 7.4 Electric Lives 18 November 2015 You are buying a new TV, washing machine and fridge. What are the most important factors to consider when choosing these household appliances?

2. Aims Look at machines that generate electrical energy and how energy is transferred. [Level 5] Use scientific concepts to explain the relative drying effects of cold and warm moving air. [Level 6] Analyse information from Sankey diagrams to evaluate the efficiency of differing forms of electrical generation. [Level 7]

3. Key words Efficiency rating European energy label Kilowatt (kW) Power Sankey diagram Watt (W)

4. Energy labels All home appliances have a European Energy Label which shows the efficiency of a machine The efficiency rating is at the top of the label People were shocked when they first saw these labels… why?

5. Mains supply Washing machine Water Drum Surroundings Case QUESTION: why could cutting down on the energy transferred as movement and sound reduce the amount of energy used?

6. Mains supply Washing machine Water Drum Surroundings Case QUESTION: would reducing the amount of water used for washing reduce the amount of electricity used?

7. Sankey diagrams Sankey diagrams show that energy transfers take place in a machine The width of each arrow represents how much energy is being transferred Energy is always conserved so the total width of all the arrows must remain the same

9. Power Energy is the ability to do work. Power is how fast the work is being done. The unit of power is the watt (W or the J/s) and the unit of energy is the joule (J) One kilowatt is 1000 W A traditional lightbulb uses 60 J of electrical energy and converts it to heat and light – its power is 60 W

11. Questions Jo has a hairdrier with two settings, hot and cool. The cool setting has a power of 600 W but the hot used 1200 J per second. If it takes five minutes to dry her hair on hot, how long would it take on cool to be more energy efficient?