Graphs

Some might:Compare efficient and inefficient devices

Energy efficiencymost should :Apply the conservation of energy to a range of appliancesCalculate the efficiency of a range of devices all must:Identify useful and waste energy typesRecall the 8 common types of energyBy the end of this lesson... Energy typesSound energyHeat energyChemical energyLight energyGravitational potential energyElectrical energy

Kinetic energy

Key wordPronunciationDefinitionConservation of energykon-ser-vey-shuhEnergy can neither be created or destroyed during a transfer of energy.Recall the 8 common types of energyApply the conservation of energy to a range of appliancesAllMost

Elastic potential energy

Learning objectives

Calculate the efficiency of a range of devices Example

100 Jelectrical25 Jlight75 JHeatCalculating efficiencyIdentify useful and waste energy typesLearning objectivesAllMost

Sankey Diagrams

Sankey diagrams summarise all the energy transfers taking place in a process. The thicker the line or arrow, the greater the amount of energy involved.

The Sankey diagram for an electric lamp below shows that most of the electrical energy is transferred as heat rather than light.

Mr Powell 2008IndexEfficiency?

How do the Sankey diagrams show which light bulb is more efficient? Describe two devices and diagrams which explain this point.Ordinary electric lamps contain a thin metal filament that glows when electricity passes through it. However, most of the electrical energy is transferred as heat energy instead of light energy.

Modern energy-saving lamps work in a different way. They transfer a greater proportion of electrical energy as light energy. Mr Powell 2008IndexSankey diagrams

10 Joules electrical energy1 square is 1 joule of energy7 squares = 7 joules3 squares = 3 joules

Sankey DiagramsHow to draw you Sankey Diagram

GET GRAPH PAPERGLUE IT INTO YOUR BOOK!Step 1) start with a blank piece of graph paper.7

Sankey DiagramsThe height of the box represents the amount of energy that is put in.Step 2) Draw a box to represent the input energy. Emphasise that it doesnt matter how long the box is.8

Sankey DiagramsThe height of the next box represents the amount of useful energy. Step 3) Draw a second box to represent the useful energy.9

Sankey Diagrams

The height of the final box represents the amount of wasted energy. But we rotate it to show that it is wasted energy.Step 4) We draw another box to represent the wasted energy, however, we rotate it around to show it is wasted. I liken this to a toilet, our waste goes downwards.10

Sankey Diagrams

Finally we add arrows to our boxes and label the diagram.Input EnergyUseful Output EnergyWasted Output EnergyStep 5) Complete the arrows and add labels.11Energy TransfersElectrical Energy10 JoulesLightEnergy8 JoulesHeatEnergy2 JoulesUsefulWastedInputThere is still 10 joules of energy available, but it now appears differently.Now for an example, an energy efficient light bulb.Now compare with a real example.12

Electrical Energy10 joulesLight Energy8 joulesHeat Energy2 joulesAn energy efficient light bulb with an input energy of 10 joules, useful output of 8 joules and a wasted output of 2 joules.What about energy?Again I asked students where they think the boxes should go.13

Electrical Energy10 joulesLight Energy8 joulesHeat Energy2 joulesWhat makes a good sankey?Arrows are labelled with input and output energies.Straight lines, drawn with a ruler.Boxes are the correct width.The wasted energy is labelled.Emphasise what makes a good sankey and what you would expect from their work.14

What is wrong?

1:301:291:281:271:261:251:241:231:221:211:201:191:181:171:161:151:141:131:121:111:101:091:081:071:061:051:041:031:021:011:000:590:580:570:560:550:540:530:520:510:500:490:480:470:460:450:440:430:420:410:400:390:380:370:360:350:340:330:320:310:300:290:280:270:260:250:240:230:220:210:200:190:180:170:160:150:140:130:120:110:100:090:080:070:060:050:040:030:020:01End1:30Mistakes: no units, not drawn with a ruler, drawn in pen rather than pencil, incorrect title, if this was for a light bulb then the wasted energy is in the wrong place, arrow sizes are incorrect, labels are not fully completed.15

Arrows are labelled with input and output energies.Straight lines, drawn with a ruler.Boxes are the correct width.The wasted energy is labelled.An example of a good sankey. Show this slide and emphasise that sankey diagrams dont have to be coloured in. I would also leave this slide up whilst students work on their sankey diagrams, as a reference point.161. Draw 3 Sankey diagrams for any of the objects that you calculated energy efficiency for. Complete the questions on the next slide in your bookssSankey Diagrams

This diagram represents energy transfer by the drill motor. The manufacturer claims the drill motor has an efficiency of 0.35. The drill motor is supplied with 3000 J of electrical energy when the hole is drilled.

What form of energy does A represent?

What does B represent and what forms of energy are included in it?

What is the useful energy transferred by the drill motor used for?

What is the useful energy from the drill motor?

What is the energy wasted by the drill?Electricalwasted thermal / soundKinetic0.35x 3000J = 1050J(1-0.35) x 3000J = 1950JMr Powell 2008Index