do now! can you finish the questions you started last lesson?
TRANSCRIPT
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 output x 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
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 heatThey 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
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
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 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 100°C
Shiny!
Brain maps again!
Brain maps again!
• Few words
• Colours
• Pictures
Brain map
Mr Porter will put the Powerpoint on loop. Can you brain-map the information?