7.4 electric lives
Transcript of 7.4 electric lives
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7.4 Electric LivesApril 13, 2023
You are buying a new TV, washing machine and fridge. What are the most important factors to consider
when choosing these household
appliances?
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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]
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Key words
• Efficiency rating
• European energy label
• Kilowatt (kW)
• Power
• Sankey diagram
• Watt (W)
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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?
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Mains supplyWashing
machine
Water
Drum
Surroundings
Case
QUESTION: why could cutting down on the energy transferred as movement and sound reduce the amount of energy used?
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Mains supplyWashing
machine
Water
Drum
Surroundings
Case
QUESTION: would reducing the amount of water used for washing reduce the amount of electricity used?
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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
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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
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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?
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