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?