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New TopicDo some revision for
tomorrow’s exam whilst you are waiting
Last lesson
Measuring the energy content of two fuelsYou will move to the next experiment at the appropriate signal.
Energy Content of two fuelsFuel Initial
mass (g)
Final mass (g)
Mass of fuel used (g)
Initial temp of water (°C)
Final temp of water (°C)
Temp rise of water (°C)
Energy released (J)
Energy released per gram of fuel (J/g)
Wax
Ethanol
Volume of water (cm3) x 4.2 x temp rise
Energy ÷ mass
Then write three sentences saying what you have discovered, and suggesting two ways the experiment could be improved.
Today’s lesson
• Sankey diagrams
• Efficiency
• What is electricity?
Wasted Energy
Wasted Energy
Can you read carefully (in silence) pages 132 and 133 of your book?
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
Energy efficient light bulb
Efficiency = 75 x 100 = 75%
100 That’s much better!
More complex examples
Let’s try the questions on pages 132 and 133
What is electricity?
Stand up!
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cell
energy
electron
lamp
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cell
energy
electron
lamp
Can you copy this please?