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Do now! Can you finish the questions you started last lesson?
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Energy transfer (change) A lamp turns electrical energy into heat and light energy
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Sankey Diagram A Sankey diagram helps to show how much light and heat energy is produced
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Sankey Diagram The thickness of each arrow is drawn to scale to show the amount of energy
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Sankey Diagram Notice that the total amount of energy before is equal to the total amount of energy after (conservation of energy)
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Efficiency Although the total energy out is the same, not all of it is useful.
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Efficiency Efficiency is defined as Efficiency (%) = useful energy outputx 100 total energy input
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Example Efficiency = 75 x 100 = 15% 500
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Energy efficient light bulb Efficiency = 75 x 100 = 75% 100 That’s much better!
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More complex examples
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You then did some questions!
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Thermal energy transfer
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Can you quickly and quietly gather around Mr Porter?
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Thermal Energy Transfer
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Heat can travel by Conduction Hot particles vibrate more, so collide with adjacent particles. The heat energy travels from hot to cooler areas. hot cold
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Heat can travel by Conduction Metals are good conductors of heat Why ?
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Heat can travel by Conduction Metals are good conductors of heat They have free electrons that can move from atom to atom carrying thermal energy too
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Heat can travel by Conduction Most gases are poor conductors of heat (insulators) Why ?
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Heat can travel by Conduction Gases are poor conductors of heat (insulators) The atoms are too far apart for the vibrations to be passed easily.
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Heat can travel by Convection
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A hot fluid expands, so is less dense, so rises. Cold fluid takes its place. A convection current can be formed.
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Examples of Convection
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Heat cannot travel in solids by convection. Why ?
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There’s one other way! ¡Uno mas!
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Infrared radiation
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Heat can travel by infrared radiation (“Hot light”!)
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Infrared radiation Infrared radiation can travel through a vacuum (and through air)
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Infrared radiation Black objects are good absorbers of infrared radiation.
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Infrared radiation Shiny objects reflect infrared radiation. Nottingham Forest winning the champions league in 1979
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Infrared radiation Which would cool fastest? 100°C Shiny!
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Let’s try! 1. Carefully fill two cans with boiling water. 2. Take their temperature every 5 minutes, filling in the table Mr Porter has just given you. Whilst you’re doing that you can do a brain map of the previous pages!
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Infrared radiation Black objects are good EMITTERS of IR radiation 100°C Shiny!
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Brain maps again!
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Few words Colours Pictures
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Brain map Mr Porter will put the Powerpoint on loop. Can you brain-map the information?
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