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© Boardworks Ltd 2003 KS4 Energy transfers and Efficiency.

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Presentation on theme: "© Boardworks Ltd 2003 KS4 Energy transfers and Efficiency."— Presentation transcript:

1 © Boardworks Ltd 2003 KS4 Energy transfers and Efficiency

2 © Boardworks Ltd 2003 Machines change energy from one form to another DeviceInput energy Output energy Dynamo Solar cell Catapult Bulb kinetic electrical lightelectrical elastickinetic electricallight

3 © Boardworks Ltd 2003 More… DeviceInput energy Output energy Microphone Loudspeaker Pendulum Motor sound electrical sound gravitational kinetic electricalkinetic

4 © Boardworks Ltd 2003 DeviceInput energy Output energy Kettle Wind-up car Coal fire Fan electrical heat elastickinetic chemical heat electricalkinetic More…

5 © Boardworks Ltd 2003 Transferring energy “Energy can neither be created or destroyed, just changed in form.” You need to be able to give examples of devices that perform specific energy changes. You need to be able to describe the energy changes for a given device. You need to remember that whenever energy is changed from one form to another, some energy is always wasted.

6 © Boardworks Ltd 2003 Wasted energy You need to remember that whenever energy is changed from one form to another, some energy is always ______. In what two forms is energy usually wasted? 1._________ 2._________ Sound Heat wasted If you can hear a device that is not designed to make noise then energy is wasted as sound. If a device gets warm and it is not designed to get warm then energy is wasted as heat.

7 © Boardworks Ltd 2003 Wasted sound energy Can you name some devices that waste energy as sound? _____________ Hairdryer Washing machine Car engine Computer Microwave Bunsen burner Wind turbine Dish washer

8 © Boardworks Ltd 2003 Wasted heat energy Can you name some devices that waste energy as heat? _____________ Computer Turbine Motor Transformer Any electrical device Television Radio Car engine

9 © Boardworks Ltd 2003 What happens to wasted energy? Wasted e_____ spreads out (d_______) into the s_________. This makes the energy harder to r____. Remember energy can not be c______ or d_______. What happens to the wasted energy you get whenever energy is changed from one form to another? This is why it is important to r_____ the amount of wasted energy there is. reated estroyed nergyissipated urroundings e-use educe

10 © Boardworks Ltd 2003 Television electrical light sound heat What are the main energy transfers for a television (don’t forget the wasted energy)?

11 © Boardworks Ltd 2003 Car engine chemical kinetic sound heat What are the main energy transfers for a car engine (don’t forget the wasted energy)?

12 © Boardworks Ltd 2003 Radio electrical sound heat What are the main energy transfers for a radio (don’t forget the wasted energy)?

13 © Boardworks Ltd 2003 Efficiency Efficiency is a measure of how good a device is at changing energy from one form to another. All devices waste energy, so the efficiency of a device is never 100%. There is a formula that allows you to calculate the efficiency of a device or of a process. Energy efficient light bulbs are more efficient than normal light bulbs because they w____ less energy, and more of the e______ energy that they are supplied with is converted into l___ energy and not h___. aste lectrical ight eat

14 © Boardworks Ltd 2003 The efficiency formula We can express efficiency mathematically using the equation: Efficiency= Useful energy out Total energy in The efficiency formula is unusual because it has no units. It is a number between 0 and 1 or a percentage. Useful energy measured in Joules (J) Total energy measured in Joules (J)

15 © Boardworks Ltd 2003 Efficiency for a bulb If you have a filament bulb and it is supplied with 100J of electrical energy which it converts to 45J of light energy. a)How much energy is wasted? b)In what form is the energy wasted? c)What is the efficiency of the bulb? Efficiency= Useful Total = 45J/100J = 0.45 or 45% 55J heat

16 © Boardworks Ltd 2003 Efficiency for a radio If you have a radio and it is supplied with 300J of electrical energy which it converts to 96J of sound energy. a)How much energy is wasted? b)In what form is the energy wasted? c)What is the efficiency of the radio? Efficiency= Useful Total = 96J/300J = 0.32 or 32% 204J heat

17 © Boardworks Ltd 2003 Efficiency for a TV If you have a television and it converts 2 000J of electrical energy into useful energy at an efficiency of 65%, a)What useful energy do get from a TV? b)How much useful energy do you get? Efficiency = Useful Total Useful = Efficiency x total = 0.65 x 2 000J = 1 300J Light and sound

18 © Boardworks Ltd 2003 In which two forms is energy usually wasted? A.Sound and light B.Heat and sound C.Heat and light D.Light and chemical

19 © Boardworks Ltd 2003 What is the intended energy transfer for a Bunsen burner? A.Sound  light B.Heat  chemical C.Chemical  light D.Chemical  heat

20 © Boardworks Ltd 2003 In what form is energy wasted for all electrical devices? A.Heat B.Electrical C.Sound D.Light

21 © Boardworks Ltd 2003 If a plant converts 200J of light energy into 140J of chemical energy by photosynthesis, what is the efficiency of the process? A.30J B.30% C.70J D.70%


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