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    Physics Unit 1a Revision (higher tier)

    Energy and electricity

    There are 9 different forms of energy:

    Light Heat Chemical Kinetic (movement) Electrical

    Elastic (Gravitational) potential Nuclear Sound

    Energy is never created or destroyed! Energy is transferred from one form to

    another form. Not all of the energy transferred by a device is useful energy.

    Potential energy is stored energy. All energy will eventually spread out to the

    surroundings as heat.

    Sample Question (taken from June 08 paper):

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    Sankey

    agramsandefficiency

    Sankey diagramsare ays frepresentingthedifferentenergy

    transformationsthattakeplacein

    differentelectricaldevices. hestart

    ofthesankey diagramshowsthetotal

    energy goingintothedevice. hediagramthensplitsoffintodifferent

    sizedarrowstorepresenttheother

    energy transfersthattakeplace,the

    iggerthearrowthelargertheenergy.

    heenergy enteringthedevicemust

    equaltheenergy leavingthedevice.

    oknowhowgoodadeviceisattransferringenergy youneedto eableto

    calculatetheefficiency. odothat youneedtousethefollowingequation

    whichwillbegivenintheexam)

    Sofortheaboveexampletheanswerwouldbe

    he closertheefficiency isto themoreusefulenergy thedeviceis

    transferring.Soforthelightbulbexamplewegotanefficiency of.1,sothe

    lightbulbisntvery goodandtransferringusefulenergy.

    EXAM TIP: Ifasankey diagramquestion comesupseenextpage)hereaquick

    way toanswerit. heefficiency willalwaysbeadecimalbetween and1e.g.

    .2, .8etc. Oncethatpartisdonetherestis justamatterofmatchingthe

    numberswiththearrowssizes,thesmallestnumberismatchedtothesmallest

    arrow,thebiggernumberismatchedtothebiggestarrowetc. Youshouldnow

    beabletoanswerthisquestionwithoutany difficulties.

    amplesankey diagramfora

    lightbulb

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    Sample Question (taken from November 08 paper):

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    Powerandelectricity bills

    Powerismeasuredinwatts W)anditistheamountofenergy transferredin

    onesecond.Soa 6 W bulbtransfers 6 oulesofenergy every second.

    oknowhowmuchelectricalenergy youhaveused, youneedtomultiplethe

    powerofthedeviceby thenumberofhoursithasbeenonfor.Soifthebulb

    hasbeenonfor 5 hoursthenithasuse 3 Watt-hoursofenergy. owever,

    theelectricity companiesusekilowatt-hours kWh)toworkout yourbill.

    Sothebulbwouldthenhaveused .3 kilowatt-hoursofelectricalenergy.

    lectricity companies charge youforevery kilowatt-hourofelectricity youuse.

    So,forexample,ifanelectricity company changes you10pperkilowatt-hourofelectricity usedthenthebulbhas cost you:

    Sample

    uestiontakenfrom March09paper):

    nergy! "

    )

    Power!W)

    #ime

    !s)

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    Heat transfer

    Heat can be transfer by $ methods

    Conduction:%

    ccurs in solids and felt by direct physical contact. The heat

    travels by the vibration of the atoms. & n metals, the heat also moves by the

    movement of free electrons or ions. Heat flows from the warm area to the cold

    area.

    Convection: % ccurs in liquids and gases. This happens because when an area

    gets hotter the particles move further apart, i.e. that area expands. Thismakes that area lighter than the surroundings so it then rises.

    'hen it then

    starts to cool that particles move closer together again and it will fall. & n short

    the hotter section expands and rises, the cool part falls. This motion is called

    convection currents.

    Radiation: All ob(

    ects do it. & t can travel through empty space (vacuum) and

    travels in waves. This heat radiation is called infrared radiation.

    You can prevent heat loss from ob(

    ects by using insulation. Air is a bad

    conductor of heat but makes a good insulator. For convection you must stop the

    heat from rising e.g. using a lid.

    Trapped air helps to prevent heat loss by conduction and convection.

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    Radiation can be reduced by using light reflective surfaces. RE)

    E)

    BER: Black

    is a good absorber and emitter of radiation but light and reflective surfaces

    and bad absorbers and emitters.

    Sample Question (taken from ) arch 09 paper):

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    Sample Question (taken from June 08 paper):

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    Generating Electricity The way electricity is generated is by

    burning fuels to heat water. This

    water then turns to steam (1). The

    steam then spins the turbine (2) which

    is connected to a generator ( 0 ). The

    generator creates electricity and

    travels to a transformer where the

    voltage is stepped up or increased

    (4). The electricity then travels down

    the electrical lines and then gets stepped down by another transformer and

    enters the home.

    Transformers:1

    hen electricity travels down the power lines some of the

    energy is lost as heat because of friction.2

    f the current was increased theneven more energy would be lost as heat (think about when you rub your hands

    together really fast). So step up transformers are used to increase the voltage

    before it travels down the line, it then gets stepped down at the other end.

    Sample Question (taken from3

    arch 08 paper):

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    Sample Question (taken from November 08 paper):

    Energy resources

    Electricity can be generated from several different resources such as wind,

    water, fossil fuels, light, biomass and nuclear. Some are renewable (can be used

    again) and other are non renewable.

    Fossil fuels are fuels which were made from plants and animals that lived

    millions of years ago. Examples of these fuels are coal, oil and gas.

    Fossil fuels need to be burned in order to be used to generate electricity. This

    is also true for biomass. The other energy resources dont require combustion

    to work but they do involve making a turbine spin except for solar. For solar

    energy the light gets converted directly into electricity.

    Energy type Renewable Causesacid

    rain

    Causesglobal

    warming

    Reliable(will

    always

    work)

    4 ther info

    5ind YES N

    4N

    4N

    4 Free energy source

    5ave YES N

    4N

    4N

    4 Free energy source

    Solar YES N4

    N4

    N4

    Free energy source

    Geothermal YES N4

    N4

    N4

    Free energy source,Creates steam

    Fossil fuels N4

    YES YES YES Needs burningNuclear-fuel is

    uranium/plutonium

    N4

    N4

    N4

    YES High decommissioningcosts, produces

    radioactive waste, no

    other pollution

    Hydroelectric YES N4

    N4

    YES Free energy source,Good for sudden

    electricity demand

    Biomass YES N4

    YES YES Free energy source

    Tidal YES N4 N4 YES Free energy source

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    Sample Question (taken from6

    arch 09 paper):

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    Sample 7 uestion 8 takenfrom March08paper):

    9 owscienceworks

    When carryingoutexperimentsandansweringquestionsbasedoninterpreting

    experiment youneedtoknowthefollowing.

    @ heindependentvariableiswhatis changedduringanexperiment

    Remembering @ ip: Independentstartswith I soitisthevariablethat I change

    @ hedependentvariableiswhat youmeasureintheexperimenti.e.theresults

    @ he controlvariablesarethethings youwanttokeepthesameduringan

    experiment.

    Whenplottingagraphfor yourresults yougenerally

    plotthedependentvariablealongthe y-axisandthe

    independentvariablealongthex-axis

    Yourindependentvariable caneitherbediscrete,

    continuous, categoric orordered.

    Dependent

    variable

    Independent

    variable

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    Continuous variables can be any number 1.2,A.7

    B,

    C.0 etc

    Discrete variables are whole numbers 1, 2,C, 4 etc. An example, you are

    investigating how the number of blades on a wind turbine will affect the speed

    of the spin. So you can have 1, 2, C etc blades but you cant have half a blade

    Categoric variables are things such as colours e.g. red, blue, green.

    D

    rdered variables are like 1st

    , 2nd

    ,C

    rd

    etc

    ***Bar charts are normally only done for categoric and sometimes discrete

    variables

    Experimental procedure

    Prediction:E

    hat you think will happenPlan: How you are going to carry out your experiment

    Conclusion: E hat you have found out from the experiment

    Fair test:E

    hen you make sure each experiment is set up the same way

    Reliable:Fn experiments you usually repeat measurement and take a mean

    (average) to make you data more reliable (trustworthy)

    Sample Question (taken fromG

    arch 09 paper):

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