All of the energy going into a device is either transferred or stored. Some gets wasted in every transfer. There are unwanted energy transfers to the surroundings. Explore 1

Have a look at these appliances and work out the missing numbers. Input Output Electricity 200 W x 20 min = 120 kJ Light = 15 J Sound = ? Heating = 100 J Television Input Output Electricity 1500 W x 4 min = 3600 J Movement = 500 J Heating = ? Sound = 100 J Hair dryer Input Output Electricity 500 W x 10 min = 300 kJ Movement = 50 kJ Heating = 240 kJ Sound = ? kJ Vacuum cleaner Explore SS1 2

Air conditioner Electric drill Washing machine SS1 Input Output Electricity 4000 W x 24 min = 5000 kJ Movement ? Heating 4000 kJ Sound 50 kJ Input Output Electricity 600 W x 2 min = 72 kJ Movement = 60 kJ Sound = 3 kJ Heating = ? Electric drill Input Output Electricity 3000 W x 100 min = 18 000 kJ Heating = 15 000 kJ Sound = 1000 kJ Movement = ? Washing machine SS1 Explore

The more energy transferred that is useful energy, the more efficient the device is. On the previous slides the RED numbers show wasted energy transfers. Explore

Rate the devices on their efficiency. You might have seen energy efficiency ratings on a new fridge or washing machine. Rate the devices on their efficiency. Explore SS1

Sankey diagrams makes things much clearer. Energy output Transferred by heating 100 kJ Energy input (transferred electrically) 2 kJ Transferred by light 15 kJ Sankey diagram for a television. Transferred by sound 5 kJ Explain

You can see that the largest arrow is heating. This is wasted energy. Transferred by heating 100 kJ Energy input (transferred electrically) 2 kJ Transferred by light 15 kJ This television is not very energy efficient. What percentage of the energy input gets wasted? Transferred by sound 5 kJ Explain 7 7

Let’s look at the different types of light bulb Let’s look at the different types of light bulb. Draw Sankey diagrams for each one and calculate their efficiency. Output energy Normal light bulb – 20 W for 10 min Energy transferred by light = 2 kJ Input energy (transferred electrically) = 12 kJ Energy transferred by heat= ?kJ Output energy LED light bulb Energy transferred by light= 11 kJ Input energy (transferred electrically) 12 kJ Energy transferred by heat= ?kJ Elaborate SS2