7j electrical circuits
TRANSCRIPT
8/16/2019 7J Electrical Circuits
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• Draw proper circuit diagrams ofworking electrical circuits usingcorrect circuit symbols.
• Make electrical circuits from circuitdiagrams (and recognise thestandard circuit symbols).
• Be able to set up simple series
circuits.• Use an ammeter correctly tomeasure current in a series circuit.
Objecties
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!hat do the following symbols represent"
#ircuit $ymbols
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Measuring #urrent
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• %n electrical current is a flow ofcharge.
• &his charge comes from electrons.
'lectrical #urrent
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• %n electron has a charge of
.*+,-). coulombs.
(,.,,,/,,,/,,,/,,,/,,,/,,,/* #)
•
0ow many electrons do you need tohae a coulomb of charge"
'+tension
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• 'lectricity is a flow of electrons.
• */12,/,,,/,,,/,,,/,,,/,,,electrons make up coulomb.
• One amp ( %) is e3ual to onecoulomb passing a single point in thecircuit eery second.
• &herefore/ for a current %/*/12,/,,,/,,,/,,,/,,,/,,,electrons must pass a point eerysecond.
'lectrical #urrent
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• '+plain the term 4resistance.4
• '+plain the changes to the currentwhen bulbs are added to circuits.
Objecties
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5esistance• %ll components in electrical circuits
hae 66666666 7 een the 66668• $ome components/ like 66666/ hae a 6666 resistance. &he 6666 wire in the
6666666 makes it harder for thecurrent to flow.
• 9utting more bulbs in 66666 willincrease the resistance and 666666the current.
!ords thin thick increase decrease highlow resistance wires bulbs filament
series
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• Use ariable resistors to alter thebrightness of bulbs.• Draw circuit diagram with current
labelled for low resistance.
• '+tension Draw circuit diagram withcurrent labelled for mediumresistance.
•
Draw circuit diagram with currentlabelled for high resistance.
:ariable 5esistors
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•
Use a flow model to describeresistance and e+plain why thelamps are brighter in some
circuits than others.
Objecties
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;nestigating #ells in $eries
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Modelling 'lectric #urrent
#ell
Bulb
$witch
5esistor
9ump
&ap
9addle!heel
<low #ontrol
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• &he 666666 in a circuit is a measure of
how much 66666666 is flowing.• #urrent is measured in 6666.
• % higher current means more 666666 is
flowing past a point eery 666666.• &he total current entering a 666666
must 66666 the total current 6666666a junction.
!ords second junction e+iting currentcharge amps e3ual electricity
#urrent
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• $tate how to connect a oltmeter.
• '+plain the term 4potentialdifference.=
• 5ecognise the potential differenceacross a component is a measure ofthe energy transferred.
Objecties
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•
9otential Difference
<inal >9'
;nitial >9'
9otentialDifference
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9otential Difference
.2 :
.2 :, :
, :
pd
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Measuring 9otential Difference
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• &he 666666666 666666666 of a
component is a measure of how much 66666 is 666666666 in the component.
• &he potential difference across the
6666 must 66666 the 666 of thepotential differences across thecomponents in a 666666 circuit.
!ords series cel l transferred energye3ual sum potential difference
9otential Difference
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1.5 V 1.5 V
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3 V 3 V
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4.5 V
9 V
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3 V 3 V
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?#onclude which two metals giethe largest potential difference.
?'+plain your results in terms ofmetal reactiity.
Objecties
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:erbal &ennis
$coring , 7 2 7 @, 7 A, 7 >ame
&opics'lectrical #ircuit #omponents
#urrent
9otential Difference
'nergy
:erbal &ennis
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'nergy 'lectricity
3000 W 1200 W900 W
100 W 50 W
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• Define the term 4power.=
• Make connections between the
power rating and current usedby appliances.
Objecties
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• &he O!C measures
how much power thescience building uses.
• 9ower is a measure
of how much energy istransferred each
second.
•
;t is measured in!atts/ or
joules per second.
'nergy 'lectricity
#lick 9icture for&rue or <alse
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. 0ow many joules of energy are
transferred each second for thefollowing appliances"
a. @,, ! teleision.
b. ,, ! microwae.c. 1. k! kettle.
1. 0ow much energy would each of theaboe appliances use in one minute"
@. 0ow much energy would each of theaboe appliances use in one hour"
A. !hat e3uation links power/ energy/ and
time"
9ower
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•
'+plain the law of conserationof energy.
• #onstruct $ankey diagrams to
show energy transfers.
• '+plain what is meant by
dissipated energy.
Objecties
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• $ankey diagrams show how much energy is
transformed to each different type ofenergy.
$ankey Diagrams
e.g. Light Bulb
100 JElectrical Eerg!
90 J"eat Eerg!
10 JLight Eerg!
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90 J"eat Eerg!
10 JLight Eerg!
10#Light Eerg!
90#"eat Eerg!
• $ankey diagrams can also be used
showing percentages.
$ankey Diagrams
e.g. Light Bulb
100 JElectrical Eerg!Electrical Eerg!
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Back to Back• Iou will compete as pairs.
• One of you will instruct the other todraw a $ankey diagram of the appliance
shown on the board.• Iou must do this erbally only.
• &he first pair to finish will draw their
completed diagram on the board.
$ankey Diagrams
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Microwae• ,,, H of electrical energy is
transformed to ,, H of heat energyin food/ and ,, H of heat energy in
the surroundings.
$ankey Diagrams
k
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Gettle• ,,, H of electrical energy is
transformed to , H of heat energyin the water/ and 1, H of heat energy
in the surroundings.
$ankey Diagrams
k
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$tereo• 2, H of electrical energy is
transformed to , H of light energy/, H of sound energy/ , H of kinetic
energy/ and 1, H of heat energy.
$ankey Diagrams
'l l f
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'lectrical $afety