Why is it wrong to say that energy is ‘lost’? Lesson link Why is it wrong to say that energy is ‘lost’?

Draw a line under last lesson’s work and write today’s title in your book... 27/11/2018 c/w Efficiency

Learning Objectives Developing Explain ways of reducing unwanted energy transfer Securing Recall and use the efficiency equation (Efficiency= useful energy transferred by device/total energy supplied to device) Exceeding Explain how efficiency can be increased

Engage Why did the Tin-Man need extra oil in order to move? ‘Lubrication’ means to coat a surface so that friction between that surface and another is reduced Explain how lubricating a motor will reduce wasted energy By lubricating a motor, friction is reduced so less energy is wasted as heat!

Here is an infrared image of a house showing where heat energy is dissipated (more red=more energy). Where is heat energy wasted in a home? Discuss with your partner ways we can reduce this dissipation of heat energy By lubricating a motor, friction is reduced so less energy is wasted as heat!

Engage Here we have two adjacent houses, write a small paragraph describing the difference between then and explain what changes the house on the left must have done!

Efficiency Efficiency is how well a device transfers supplied energy into useful energy. For example, we provide light bulbs with electrical energy to produce light energy. So a bulb that produces lots of light without much heat would be very efficient indeed! Standard: Price 60p Energy Saving: Price 120p Explain which bulb type we should all be using by comparing a standard bulb (left) with an ‘energy saving’ bulb using the data shown.

Calculating Efficiency Efficiency is how well a device transfers supplied energy into useful energy. So in order to calculate the efficiency (as a percentage) all you have to do is divide the useful energy transferred by the total supplied! Efficiency (%) = Useful Energy Transferred Total Energy Supplied Calculate the efficiency of this standard bulb This is a Sankey diagram and is used to represent the energy transfer taking place!

Calculate the efficiency of this standard bulb The total energy supplied is the energy coming in. In this case it is 100J of Electrical Energy The useful energy here is the light energy as we don’t want the heat! So this is 10J Useful! Note: the total energy may sometime be called ‘input’ and the useful energy may be called ‘output’ As efficiency= useful / total = 10J/ 100J = 0.1 (aka 10%)!

Time to practice… Complete all the questions on the sheet provided. Make sure to show all your workings!

Exam Practice 1a) A lamp has a label attached saying that it has an efficiency of 20%. Explain what this means. (2 marks) .......................................................................................................................................................................................................... b) Draw a labelled Sankey diagram for the lamp. (3 marks)

Exam Practice 1a) A lamp has a label attached saying that it has an efficiency of 20%. Explain what this means. (2 marks) Only 20% of the total energy is transferred into light energy, the rest is wasted as heat energy b) Draw a labelled Sankey diagram for the lamp. (3 marks) See board

Learning Objectives Developing Explain ways of reducing unwanted energy transfer Securing Recall and use the efficiency equation (Efficiency= useful energy transferred by device/total energy supplied to device) Exceeding Explain how efficiency can be increased

Independent Study Write a letter to a house-owner to inform them of changes that they can make that would increase the efficiency of their household. Explain the science behind your suggestions