Do now! Can you finish the questions you started last lesson?
Energy transfer (change) A lamp turns electrical energy into heat and light energy
Sankey Diagram A Sankey diagram helps to show how much light and heat energy is produced
Sankey Diagram The thickness of each arrow is drawn to scale to show the amount of energy
Sankey Diagram Notice that the total amount of energy before is equal to the total amount of energy after (conservation of energy)
Efficiency Although the total energy out is the same, not all of it is useful.
Efficiency Efficiency is defined as Efficiency (%) = useful energy outputx 100 total energy input
Example Efficiency = 75 x 100 = 15% 500
Energy efficient light bulb Efficiency = 75 x 100 = 75% 100 That’s much better!
More complex examples
You then did some questions!
Thermal energy transfer
Can you quickly and quietly gather around Mr Porter?
Thermal Energy Transfer
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
Heat can travel by Conduction Metals are good conductors of heat Why ?
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
Heat can travel by Conduction Most gases are poor conductors of heat (insulators) Why ?
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.
Heat can travel by Convection
A hot fluid expands, so is less dense, so rises. Cold fluid takes its place. A convection current can be formed.
Examples of Convection
Heat cannot travel in solids by convection. Why ?
There’s one other way! ¡Uno mas!
Infrared radiation
Heat can travel by infrared radiation (“Hot light”!)
Infrared radiation Infrared radiation can travel through a vacuum (and through air)
Infrared radiation Black objects are good absorbers of infrared radiation.
Infrared radiation Shiny objects reflect infrared radiation. Nottingham Forest winning the champions league in 1979
Infrared radiation Which would cool fastest? 100°C Shiny!
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!
Infrared radiation Black objects are good EMITTERS of IR radiation 100°C Shiny!
Brain maps again!
Few words Colours Pictures
Brain map Mr Porter will put the Powerpoint on loop. Can you brain-map the information?