7J Electrical Circuits

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



!hat do the following symbols represent"

#ircuit $ymbols



Measuring #urrent



• %n electrical current is a flow ofcharge.

• &his charge comes from electrons.

'lectrical #urrent



• %n electron has a charge of

.*+,-). coulombs.

(,.,,,/,,,/,,,/,,,/,,,/,,,/* #)

•

0ow many electrons do you need tohae a coulomb of charge"

'+tension



• '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



• '+plain the term 4resistance.4

• '+plain the changes to the currentwhen bulbs are added to circuits.

Objecties



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



• 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



•

Use a flow model to describeresistance and e+plain why thelamps are brighter in some

circuits than others.

Objecties



;nestigating #ells in $eries



Modelling 'lectric #urrent

#ell

Bulb

$witch

5esistor

9ump

&ap

9addle!heel

<low #ontrol



• &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



• $tate how to connect a oltmeter.

• '+plain the term 4potentialdifference.=

• 5ecognise the potential differenceacross a component is a measure ofthe energy transferred.

Objecties



•

9otential Difference

<inal >9'

;nitial >9'

9otentialDifference




.2 :

.2 :, :

, :

pd



Measuring 9otential Difference



• &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




1.5 V



1.5 V



1.5 V 1.5 V



3 V 3 V



4.5 V

9 V



3 V 3 V



?#onclude which two metals giethe largest potential difference.

?'+plain your results in terms ofmetal reactiity.

Objecties



:erbal &ennis

$coring , 7 2 7 @, 7 A, 7 >ame

&opics'lectrical #ircuit #omponents

#urrent


'nergy

:erbal &ennis



'nergy 'lectricity

3000 W 1200 W900 W

100 W 50 W



• Define the term 4power.=

• Make connections between the

power rating and current usedby appliances.

Objecties



• &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



. 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



9 O & ' E & ; % C D D #

O D $ C ! O C F G ; 9 U

! % & % 5 G B # $ < # 5

' ' D $ C % $ H & < U 5

5 I ; & ; I % 9 M ' ; '

; U $ ; 9 C J 5 U 5 : E

' H C # O M 9 O E ' E &

! O 0 U ! > C M E E B >

E U C B M # 9 $ O # & C

D C < $ D ' : ; # ' E D

$ ' 5 F B C M > ! < O U

# $ $ # G C M # ' ! M 9

9

O

!

'

5

9 O & ' E & ; % C D

I

F

F

E

RE

N

C

ED ' : ; # '

# O M 9 O E ' E &

#

U

5

5

'

E

&

#

'

C

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H

O

U

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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



• $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!



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!



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



Microwae• ,,, H of electrical energy is

transformed to ,, H of heat energyin food/ and ,, H of heat energy in

the surroundings.

$ankey Diagrams

k



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



$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



'lectrical $afety



• #omplete ;ncomplete #ircuits.

• $eries and 9arallel #ircuits

• %mmeter and :oltmeter 5eadings.

• 0ow #urrent #hanges in $eries#ircuits when Bulbs are %dded.

$cience8

7J Electrical Circuits

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