KS4 Energy transfers

Transducers change energy from one form to another Device Input energy Output energy Dynamo Solar cell Catapult Bulb kinetic electrical light electrical elastic kinetic electrical light

Device Input energy Output energy Microphone Loudspeaker Pendulum Transducers 2: Device Input energy Output energy Microphone Loudspeaker Pendulum Motor sound electrical electrical sound gravitational kinetic electrical kinetic

Device Input energy Output energy Kettle Wind-up car Coal fire Fan Transducers 3: Device Input energy Output energy Kettle Wind-up car Coal fire Fan electrical heat elastic kinetic chemical heat electrical kinetic

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.

Wasted energy You need to remember that whenever energy is changed from one form to another, some energy is always ______. wasted In what two forms is energy usually wasted? 1._________ 2._________ Heat Sound 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.

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

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

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

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

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

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

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%. 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 There is a formula that allows you to calculate the efficiency of a device or of a process.

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)

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. How much energy is wasted? In what form is the energy wasted? What is the efficiency of the bulb? 55J Efficiency = Useful Total = 45J/100J = 0.45 or 45% heat

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. How much energy is wasted? In what form is the energy wasted? What is the efficiency of the radio? 204J Efficiency = Useful Total = 96J/300J = 0.32 or 32% heat

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%, What useful energy do get from a TV? How much useful energy do you get? Efficiency = Useful Total Useful = Efficiency x total = 0.65 x 2 000J = 1 300J Light and sound

Assuming no energy is lost by air resistance!!! Falling objects When an object falls in a gravitational field: Gravitational Potential Energy (GPE) at the top equals the Kinetic Energy (KE) of the object just before it hits the ground. So if a diver has 4 000J of GPE on top of a cliff, how much KE will she have just before she hits the sea? _________ Assuming no energy is lost by air resistance!!!  4 000J

In which two forms is energy usually wasted? Sound and light Heat and sound Heat and light Light and chemical 

What is the intended energy transfer for a Bunsen burner? Sound  light Heat  chemical Chemical  light Chemical  heat 

What is the energy change for a falling rock? Kinetic  gravitational Gravitational  kinetic Kinetic  speed Mass  speed 

In what form is energy wasted for all electrical devices? Heat Electrical Sound Light 

If a plant converts 200J of light energy into 140J of chemical energy by photosynthesis, what is the efficiency of the process? 30J 30% 70J 70% 