Download - Physics Unit 1a Revision Higher Teir
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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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