KS 4 Energy transfers and Efficiency Boardworks Ltd

KS 4 Energy transfers and Efficiency © Boardworks Ltd 2003

Machines change energy from one form to another Device Input energy Output energy Dynamo kinetic electrical Solar cell light electrical Catapult elastic kinetic Bulb electrical light © Boardworks Ltd 2003

More… Device Input energy Output energy Microphone sound Loudspeaker electrical sound Pendulum gravitational kinetic Motor electrical kinetic electrical © Boardworks Ltd 2003

More… Device Input energy Output energy Kettle electrical heat Wind-up car elastic kinetic Coal fire chemical heat Fan electrical kinetic © 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. © Boardworks Ltd 2003

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

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

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

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

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

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

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%. Energy efficient light bulbs are more efficient than normal aste less energy, and more light bulbs because they w____ lectrical energy that they are supplied with is of the e______ ight energy and not h___. converted into l___ eat There is a formula that allows you to calculate the efficiency of a device or of a process. © 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) © Boardworks Ltd 2003

Efficiency for a bulb If you have a filament bulb and it is supplied with 100 J of electrical energy which it converts to 45 J of light energy. a) How much energy is wasted? 55 J b) In what form is the energy wasted? heat c) What is the efficiency of the bulb? Efficiency = Useful Total = 45 J/100 J = 0. 45 or 45% © Boardworks Ltd 2003

Efficiency for a radio If you have a radio and it is supplied with 300 J of electrical energy which it converts to 96 J of sound energy. a) How much energy is wasted? 204 J b) In what form is the energy wasted? heat c) What is the efficiency of the radio? Efficiency = Useful Total = 96 J/300 J = 0. 32 or 32% © Boardworks Ltd 2003

Efficiency for a TV If you have a television and it converts 2 000 J of electrical energy into useful energy at an efficiency of 65%, a) What useful energy do get from a TV? Light and sound b) How much useful energy do you get? Efficiency = Useful Total Useful = Efficiency x total = 0. 65 x 2 000 J = 1 300 J © 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 © 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 © Boardworks Ltd 2003

In what form is energy wasted for all electrical devices? A. Heat B. Electrical

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