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Topic 4

o1 ,Eectricity',Magnetismo

'.''''."'

W 4.1 Magnetisml} 4.2 Electrostatic

0 4.3 Electric Circuits

IJ' 4.4 House Installation and. Electric EnergyI..w"

Magietic Effects and Motors4.5r"

"4.6 Induction and A.C. Generators

4.7 Transducers and, C.R.O

f, •

,..

Maged Louis 4.1 Electricity Magnetism1 You are given an iron bar, a reel of insulated wire, a battery and some wire cutters.

June2000 ~

iran bar reel ofinsulatedwire

battery wire cutters

Fig. 3.1

(a) In the space below, describe how you would make an electromagnet. You may use a" labelled diagram it it helps you to answer the question.

Ha.k~Q COli ~ &i W,'YC::

orDvn"d ~ \Yon baravJ \{ 05Mj w1ter YYyJ~

~ Terrn1~~~ D~ ~ GJ\~

~~ f-o b eo", Y'e c.kcJ...............................................1P. .gg;. ····S··d.. 'r4 .

ty r- '1\

.: ::::::::::::::::::::::::::::::::::::::::::::::::.: :2:::::::::::::: :::::::::::::..'. ::::::::::::::;~;(b) How would you check that your electromagnet actually works?

........... : 1,.. .h.a .ct....Irnn.. !e b.at,) :i. 8:rdf.~ .

..................y. . . ..::boo t···L.t:····~·····adtr.4" '~3F:;~ .

.......................... , ~ .9. ..1. ~ :::=.:..::~

Magcd Louis 4.2 Elcctr icity Magnetism2 . Fig, 7.1 shows one way of using water to generate electricity.

(a) Fill in the missing words in the boxes. r::::' June 20001i"J [4]

reservoir

pipe

(I)

~(Hi) The water rotates the.-,-. b ~......!.U .f.. .. J. f.W..S .

so that the generatorprOduces

I ..·..~~;~~~······energy becauseof its height.

'P. ·E'.•............................

(1/)

.......k':~.£~....~,..... '..~I:.:'. I~ ••

'...

.:.:.:~....::;:: ..:.,..:;-:: .:, :.~energy.

Fig. 7.1

(b) In other places, water is used in different ways to generate electricity.State two of these ways. '

1. .....................................~ = . ..~[ ..s.:".: .2. . . '"·J [2]

3 A Ittborntory tochnician wants to make a resistor of value 64 n, using some resistance wire.Ho tnKOS 1.0 m of this wire. The wire is shown in Fig. 10.1 as AC. He connects up the circuit

ehown. June 2000

(\~A

vuniformresistance

.wire

CA 0.5m

crocodile clip

Flg..10.1

:.

Magcd Louis 4.3 Electricity Magnetism(a)' He connects the crocodile clip at B, which Is 0.5 m from A. [\~

Here are the readings he gets.

voltmeter reading 12 V ..

1:5 A. ammeter reading

Calculate the resistance of wire AS .

.~:::~t12/\.S

-8Sl-

·-1,.ANSWER: resistance of AB = .. n (3)

(b) The laboratory technician now connects the crocodile clip to C, to measure L'1eresistance of 1 m of the wire. The wire has constant thickness.

(I) In the spaces below, write the readings he obtains. Ignore the effects of theresistance of the ammeter, voltmeter and battery.

voltmeter reading ..J.~ V

ammeter reading .9.0'..1:..? A(II) What is the resistance of wire AC?

.. . \.6ANSWER. resistance of AC = n [3]

(c) Use your answer to (b) to answer the following questions.

(I) What Is the resistance per metre of this wire?

~~~ G{~~

~v -eCl~ ~

A~~$;

~ 'l'esld-~~ ~

IS '6 SL

1n..~',5 ca~\ s i m,ekv--

ANSWER: resistance per metre = ....LG. ... illm

(II) What length of wire does the laboratory technician need lor the 64 n resistor?1m ~i6JL ,.X --7 G'-i SL 4

ANSWER: length needed = ~ m [31

Maned Louiso

4 The circuit in Fig. 9.1 is connected up.

4.4 Electricity Magnetism

rNoV. 2000

.20n1

6VlI

-L.

'\, Fig.9.1. .

(a) Calculate the combined resistance of lhe two resistors in Fig. 9.1.

=--=

combined resistanca.e .....~.Q.....o (2J

(b) (i) State the relationship between resistance, p.d. and current by cornpletinq thefollowing equation.

P·d~resistance = _Q;. '(('eN\J

(ii) Calculate the current, /, in Fig. 9.1. State the unit in your answer,

VT _..L... r-.

RGv-- ..,.-..

GO..n. 0.1 A

0.1.. Acurrent = .

[5'

4.5Magcd Louis Electricity Magnetism

(c) Use your answer to (o)(ii) to calculate the p.d. across the 40 [l resistor.State the unit in your answer.

l?'1"- LtO.-SL resi'd''\)r'R~ Lt05L

~-= 0.1 A-V::= 1< I ~L; 0 x: 0, I

..=- . D.. vo l-h

.p.d. = ~ V [3}

(d) The circuit is now used as a potentlaldivlder •.as shown in Fig. 9.2.

20n(

6V'I

-L-

·T40n Vout

Fig. 9.2

Use your answer to (c) to state the value ol Vout • the output voltage ol the potentialdivider. y

VOU1 = X V [1)

Maged Louis 4.6 Elc ct r-ici ty Magnetism5 (af (i) Copper is aC} electrical conductor. What is me ant by a conductor? Nov. 2000 ®

..........\.~ ..a1.L .. ..s \.(.ctr.( ..c CU~ ..(.dtQv.-WJ ..t..£Lo.~(ii) Ebonite, glass and polylhene are electrical insulators. What is meant by an

. insulaior?

.......5.u1 fuVl.Ce.. . .... d.9.... L ..cll9.!¥..d!)<:\1f..>. ...@p<J...~~'1J~[2J

(b) Polythene is easily given a negative charge by rubbing it with a dry woollen cloth.

(i) Fig. 11.1 shows a charqedpolythene rod being heldclose to a suspended charjjcdpolylhene rod.

nylon thread

Complete the phrase,

UI'k h rcMt ,.'"I e c arges i:-:;-; ••••••.••

negativelycharged polythene

Fig. 11.1

(ii) Fig.11.2 shows rod X beingheld near the suspendedcharged polythene rod.

Tick any 01 the following whichmight correclly describe rod X.

----.negativelychargedpolythene

positively charged glass 0negatively charged ebonito 0uncharged copper 0negatively charged polythene 0

Fig. 11.2

[3J-------------------.--~------...----.... ,.

4.7 .Muged Louis Electricity Magnetism

6 "A charged ebonlle rod has negative chiuges all over Its surface. It Is held above three smallpieces "at aluminium fall, one positively charged, one negaUvely charged and oneuncharged. This Is shown in Fig. 6.1. .

ebonlte____________ "~ .•.• / r~dI r---------------------------

June 2001

rf)

j!

, (;;) Ii

posliive

Insulating,g", ,/sheet

no charge, ,",&:t,negative

Fig. 6.1

(a) Put a circle around any of the pieces of aluminium which are attracted by the ebonlterod. " [2]

(b) Ebonite Is an Insulator. What is'rneant by the term insulator?

... ~ .l, 0. $"••• ....,.:a.l.L ..ete.. ..ceJ: ~... f.1. ~ [2J~ .

.<c} Write down the name of anotherlnsulatlnq rnaterlal.

............................................. [1]

7 Three resistors are connected in series between X and Y. When a cell is connected acrossXY, the current at X is 0.1 A, as shown in Fig. 7.1.

June 2001

\D

F/g.7.1

(a) What is the value of the current at Y? .1 A [1 J(b) Calculate VI' the p.d. across the 12 n resistor.

Y,==- R X 1= 12 X 0·1::2.. p.d. across the h n resistor = ..J~.q., v [2J

(c) What Instrument would you use "to measure the p.d. VI?' J+.m.£..~ [lJ

(d) How does the e.m.t. of the cell compare with your answer to part (b)? Tick one box.

e.m.f. of cell Is larger Ihan VI [2Joo

[lJ

e.m.t. of cell Is smaller than V1

e.m.f. of cell Is the same as V1

(e) Calculate the combined resistance of the three res/stars.. "

c.. c: \2 1- S -+ :1 -=2 combined reslstance = .g (1 [21

Maged Louis

B (a) Fig. 8.1 shows a simple transformer.

4.8 Electr-icity Magnetism

core

June 2001

(IJ

callNp turns

callu, turns

Fig. 8.1 Va = V

Complete the following sentences about the transformer.

t ~~'The transformer only works ~$.I~g.;.;.._... _.", f•••••••••••\~r.(] current."

It steps the potential difference up or-down according to the equation

Vp_ Np ..Va - Ns

- cThe core of the transformer Is made at J.CQ.Y.\.: .' [3j

(b) In each of the following examples, state the potential difference Va'

(I)

100 turns 50 turnsVa = 6. V

(II)

80 turns 80 turns"VI = V

(III).

6V~. ¢k=v.80 turns 80 turns

v. = ..-:?~9.....V[4J------------'--------:------------------ -

·Magcd Louis9 . (a) Three metal reds look thesame.

4.9 .Electricity Magnetism

One is made of aluminium.One is.made of unmaqnetlseo iron.One is a permanent magnet.

Nov. 2001

GDescribe how a small bar magnet could show which, rod is

(i) made 01 aluminium,

••••••••••••• •• • ••••• t •••••••••• .Q...... .•......I\..r.y.'••••

.••••.••.••••.•• ! •••••.••••.•••.•.•••••.••••.•.••.•••••••••••••.••••.~•.•••.•••••••••••.••••••.••••••••.•••••••.••.•••••••.•.••.••••.••.••••.•••••.•..••.•••.••••.•••••..••••••••..••••.••.•.•.••..•••••••.••.•••••.•.•••.•••.••.•••••.

(II) made of unmagnetised iron,

...........g. ~ ',"'-"'.v.'- .

.......................................................................................................................................:,(Hi) a permanent magnet.

A '-/.\ I.•• :n _ \.~ o.n~ ~.1.~ ~\ .

.~L d~ ~ ~ " [4]

(b) In an experiment, a steel ball-bearing 'is held up by an .electromagnet,· as shown inFig.6.1.

§ electromagnet

~ steel ball-bearing

Fig.6.1

The electromagnet then releases the ball-bearing, whlch falls to the floor.

(i) From what metal is the core of the electromagnet made?

{l . ~'".:tt..mt11Mtl.~ ~~ ............· lC ~ .

(ii) How is the electromagnet made to work?

...:±l.[.Jl....~~LX.. •••••••• ~s..£~~.ld..."1111 .••." ' •• 1?IJJ '~~.

(I.Ii) What is done to make the electromagnet release toe ball-bearing?

....................~.J:p :. . + [3]-------------'--------------- ._. -- .-

.. ,'

4.H)Maged Louis10 This question 1s about the dangers of electricity,

Elcctl'icity Magnetism

Nov. 2001(8) A builder tries to save money by' nor-fitting fuses or circuit-breakers to the electric

circuits in a house. Why might this be dangerous?

............:, 1h<.-.... J :' .kr..... .J~k :Th.~ .• •••••••••• • •• ••• • • • •••••• •,'w<~ •.•n;...""..-\.... • . ••• ••• •~J~.... . (J....... e.\.f.f... . .

. £U ."u{.'Ce ~e.tt. ~. : ~ ...9..vw.:.f-{~J..~(fj'~J(b) Another builder only has switches like the one shown in Fig. 7.1.. .

Fig.7.1. .

The builder decides it might be dangerous to fit one of these switches in a washroom,where there would be water and steam.

Why might it be dangerous?

····..····..·····,···········±Of·····'x<!· Y..... . . .9.. d.v.~ ~ :.............................. .e cJ.~..':.·: _ .................................da r, •••••• 9.: :efe :.("G~Q.cK [21

(c) A cleaning operator is trained to check the cable 01 a vacuum cleaner for damagebefore it is used.

Why might it be dangerous to use equipment with a damaged cable?

....................................le ~..~ I••?.c.k: .

.................... : ; '";'; (1]

. 4.1 r,Magcd Louis Electricity Magnetism1'1' A student draws the circuit shown in Fig. 9.1. The circuit is intended to be used to measure

the resistance of R, a length of nichrome resistance wire.

·zNov. 2001

\CD

Flg.·9.1(a) The student cannot remember which meters he should use at X and at Y.

(I) Which meter should he show at ·X? Ctf.b..m. J{r. .

(II) Which letter should he put in the circle at X? 6. .(iii) Which meter should he show at Y? VQH·.meif ..(iv) Which letter should he put in the circle at Y? V .

'..,' . . [4 J

(b) (i) What is the component labelled z?-.'~............ i.sfuc .(ii) What is the purpose of Z in the circuit?. ba .§f.(.(9.njy~.0..ih ..~r.~~t

'. lot. c1nQV\.5fA::; ~ ~.sIS tdtnU2 [3J

(c) The student connects the circuit and obtains the grap~ ~hown In Flg.9.2.

4.0lj~~~~~~~~~~~!f~~~p.d.1V 3.0 ., ' .

2.0

1.0 -++__+_hI4_ .+-..f+:l,.+'H.+.H. +.. +-.H.+.+..H.+..t+t+H. +rooM...ffi_ttti

o~~~·[·t~··~:~~:~·~..~·i--H-·~·~..K·~:·H±~~~o 0.1 0.2 0.3 0.40.5 0.60.7 0.8

current! A·Flg.9.2(I) How can the student use the- graph to find the resistance of R 7

..................f!:!!J : .. 0. (E, J¥ .

...............t: er. \/1. ~~ I·~..v:....... . .a .~.~ :ts .v L-1.. \A."-l'... .••.. if ..· J. U CU~ :.R..;;:..}, .

(ii) Calculate the value of R ..

R::::-jL, = l =-5,SLr O.G . resistance R = !;? ~ [4]

(d) The student removes the length of nichrome wire R and replaces it with the same lengthof thinner nichrome wire. .

(i) Will the resistance of this wire be greater than, smaller than or the same as the wirein the rest of the question?

Q r" th................... ,.............•................. .:::J. . . Af!. · ··..·9n .. (if) On Fig. 9.2. sketch a line which the student might obtain when he repeats the

experiment with the thinner wire. [3J

4.13Magcd Louis Electr-icity Magnetism13 Fig. 7.1 illustrates one country's system ror transmitting electricity around the country. from

the power station to people's houses ..June 2002

voltage here22f) V

000000 EII -- ". 1--..IC..-.-;L.:l.

power station step-up grid systemtransformer

step-down step-down housetransformer transformer .

Fig. 7.1

(a) At diflerent points in this system, the voltage is 220 V, 11 000 V or 132000 V. At the threeplaces marked on Fig. 7.1, write In the appropriate value of the voltage. [3J

(b) State one advantage of using hi'gh voltages for the transmission of electricity .

.. s:.s. .

. .................•............. [1J__________ ~L- ---- ----_---- __

14 Ag. 3. ~ shows a vertical wire through a horizontal piece of card. There Is a current down the'>'Jire.

largecurrent

Nov. 2002

Fig. 3.1

cardAg. 3.2 shows the wire and card, viewed from above.

Fig. 3.2

The large circle Is one of the magnetic field lines caused by the current.

On Ag. 3.2,

(a) show the direction of the magnetic field,

(b) carefully draw three more magnetic field lines.

[11

[2]

r,,]aged Louis 4.14 Electr-icity Magnetism15 (a) Fig. 9.1 shows, a circuit that includes three ammeters. The resistance of the ammeters

and the battery can be ignored. . .

June 2002

.----1 ~- -1\~--------, ck.-~-,I~

Fig: 9.1

(I) What Is tho total resistance of the circuit? (Y erf.e..r. ~

R c~ q;( \ 1" R'1 = 2.0 -t-..2 't) resistance = ~.Q n

(ii) Ammeter AI reads 0.2A. Whatdo the other two ammeters read?

.' A2 reads ...Q:? A

<'.2A3 reads :.. A(31

(b) Fig. 9.2 shows tho same components as in (a), but connected differently.

200

Fig. 9.2

(I) What Is the total resistance of tho circuit? Tick one box ...L~ '2 ~..LRc..- T - \0

Rc =- \0

400 D300 D200 010n ~

(iI) Ammeter AI reads 0.8 A. What do the other two ammeters read? Tick theappropriate boxes.

more than 0.8 A a.8A loss than 0.8 A

A2 reads V'

A3 reads ,j/"

[3)

4.15·Magcd Louis Electricity Magnetism16 A student holds ~ polythene rod In one hand and a dry cotton cloth in the other.

dry cottoncloth

Fig. 7.1

"- __ polythenerod

Nov. 2002

(8) How can the student cause the rod to become charged with static electricity?

.........................................ub ~.~ ..:];Q3.f.Jf.\f. [1]

(b) How can the student detect that the rod has become charged?

...J;l.i.~ f~g,e.dg;p.kr):f0J rJe. (Q.pg •./. ~.~ h~.c r..!~. . Dr pfcIL vp fl\,d~

(c) Around the charged rod will be an electric fJeld."

What Is meant by an electric field? '.

............~ l.t \.~ 9. c.g J2.Y.)0r..?~rJ.J..~ ..f.f..d:r.~S ~9.r.~ .••••.••..... ~.IJ...•~~.rb O= ~P.s x:L~. . 0...:.&: ~ ~ [2]

(d) The charged po!ythene rod is brought close to another charged polythene rod that hasbeen suspended from a nylon thread, as shown In Fig. 7.2. .

nylonthread _chargedpolythenerod (..:.)

charged"--- polythenerod (-)

(I) What Is seen to happen to the suspended rod?

.~ f.t.m ~ .:gw.~¥ : .(II) Explain why this happens .

...... .1.. ~tJ c.!.Jt.J. ~.d.. : .. [2]

(e) If the student used a copper rod In (a), lnsteadof the polythene rod, why would he notbe able to charge the rod?

....................(;q?p.. c. :~ Q C. .. .••••••••••••••..••••••••••• ~.... • • :-f.. ••••••• Sl....... aa J. [1]

'" .

Magcd Louis 0 4.160

Electricity Magnetism17 Ago.8.1 shows an electric circuit containing a battery. a 4.7 0 resistor, an ammeter and a

variable resistor with a sliding contact. The variable resistor is set at zero. The ammeter andbattery have such a small resistance that it can be Ignored.

Nov. 2002

variableresistor A

y

4.70

o Fig. 8.1

(a) In what unit do we measure the e.m.f. of the battery? .•..•......\f.. J±~ [1J

(b) Write down the equation that links res/stance, potential difference (p.d.) and current

R~SiSivnCQ <;;;:' 'PoteVl.--n'ct\ d,.,rte.v'e0(Y'€..h-t

(c) The ammeter shows that the current through the 4.7!1 resistor is O.SA.

Calculate the p.d. across the resistor.

V= R r ~'1-X 0,5

p.d. across resistor = ?:.~?y.. [21

(d) The sliding contact of the variable resistor Is moved from X to Y.

(I) What happens to the resistance of the variable resistor?

............................................... R2:>..!:e..trJ rl-.!i. •••. ' .•• (ITa .... .:±9...N!*.i.r.!uy(lI) What happens to the reading on the ammeter?

.........................M .. J.a:J...... . (. ..1:c m.f.rJ.l.D:1.I!.~ .~ 0 - [2)

(e) The variable resistor Is now adjusted to make the total resistance of the circuit 10.0n.What is the resistance' of the variable resistor now?

I~- 4.7 -::::::s.-:;

resistance of variable resistor = ?.~.~ n [2]

4.17 "Magcd Louis Elect'deity Magnetism

18 {e) The apparatus shown In Fig. 10.1 can be used to Indicate when there Is a force on the

cop~rrod,r---', - Nov.2002 h:::J~ hanging copper rod '

'T'" I,

I

mercuryFig. '10.1

(I) Suggest what Is seen to happen to the hanging copper rod when the switch Isclosed. ' '" ,

r\- OV',' ,•••••••••••••••• •• •• •••••••• J••••••• m , e..s., : ....................................................................................................................................

(if) ExplaIn your answer.

£P nti rr J _"k '~ \ .£:.. _......~.~~..L.p .c p~c.ARf.: ~pey.]eM .L:J.l)f.~..J.~

...I/.'()j7j G :-B.d .(iii) The celf Is reversed and the switch closed..~

.." .

CQ1')m Loltcdo r

l3rus hcoli

fb(I) In the boxes, label the various parts at the motor. One part has been labelled as an

example.

(iI) Which part of the motor ensures that the coli keeps rotating when the battery Isconnected?

"Fig. 10.2

.................................. .m.m... ..Q.jJ .c : . .(III). The battery Is reversed. What difference does this make to the motor? "

.......•.•. f.'JJ. .'{g (.... ··f:iik0.···....N.Q .~t.b!.~ frg!):!:i.dack:.Lv tS-e

4.18 . Electricity MagnetismMaged Louis19 (a) Rg. 11.1 shows a reed relay In a simple circuit.

lampflexible Nov. 2002iron reeds

Fig. 11.1

Explain why the Iron reeds touch'each other when switch S Is closed .

.::jhe ~le.cl:o~...-.CUmJ ....~ ..th~ ...(4)\\....~ ... . ~tJR.h~ ...£:e1d .

..£ ~..n. ~e.eJ.s.~.n.eli d;;)..a- ~ .C t..ewl~... was~i .

...p.. .\ar:!l~ ...s evJ~ :ttratd .ea.' .9.llia [4}(b) Fig. 11.2 snows a simple temperature-operated alarm.

warninglamp

Fig. 1~ thermistor,,

When the thermistor Is cold, Its resistance is too high to allow sufficient current tooperate the reed relay. The resistance of the thermistor decreases as the temperatureIncreases. .

Describe what happens to make the warning lamp light as the :alr. temperature changes .

...............W.he t .l)-)~R.ttu.~ J.•r .r. ;/"..~ttl£f.Jl).· h.r:.r ·. ~c,. (e

..............c1:e.c.~ I- •.~. ..•.e...~ CM.«:e. ....fXlZ.<.l.±~ ...ck:e ~.................. JC~~ / ~.t...u..u:r.e~..::fLa.w. i~..~... . , xlhl .....; ~..c: .)c,".~ ·i s:c;;:;> ••••• ~ ••• Rar.~ ~h..t....s; ..t:••••••••••••••••••••••••••••• : •••••••

•••••••••••••••••••••.•••••••••••••••••••••••••••••••••••••••••••• ; •••••••••••••••••••••••••••••• r ••••••••••••••••••••••••••••••••••••• [4]

""'!

Mugcd Louis . 4.19" Electricity Magnetism c\cp.rlf )20 (a) . In an electronic circuit, what is a capacltor designed, to store? ....E(.\~j ...(~~....[1,

(b) The circuit in Fia. n.1 contains u large·valup resistor and a capacitor.

June 2003

~larqc-valuoresistor

6V d.c.

(-capacitor =,=]..'S2

>--.

". Fig. 8.1

(i) Switch Sl is open. Switch S2 is closed and then opened again .

What reading now shows on the voltmeter? ............Q v(ii) S2 is left open and S I is closed and left closed.

Describe what happens to the reading on the voltmeter.

...............R.f<:l.(.\. e,>. ••• '" 6. ..v. f illlj":fum ?&!t.? .

.......................................... ;G..v..~ .(Ill) The circuit in Fig. 8.1 is an example of a simple time-delay circuit.

State one use of a time-delay circuit.

........................~.:e1£cbf.\..(.~-:e,~ ~'rn.a..c. .

..... .Y:e.rt t~F"." .__________ -\-(-J..:.s~c.1.!...lrois::...:e~!C..· v="j.!<j--,-::b~V(~ On (Q.£L _-.l4_1_

q8e,v ~ -hfWi- ~ -)

4.20 .Magcd Louis Electricity Magnetism21 A length of flexible, slack wire is fixed al A and B so that part of it is held vertically

in the field 01 .a horseshoe magnet, us shown in Fig. 9. ~.

June 2003

"

B

Fig. 9.1

Figs. 9.2 and 9.3 each show the same section through the apparatus. The wire between Aand B is not shown. -

, Fig. 9.2 Fig. 9.3

(a) (i) On Fiy. 9.2. draw what the wire might look like when a large curreni passesthrough it. [2)

(ii) Explain why the wire looks like this. ,

.:11/".~." ..ck ..::ku.ffin..::b:a.d~...QY.l ... :tb.u ...w.~.. ~c ~,'e(J~~.ck \.<" .•• .a, Cu.v..~ ~.(aIC0~""Co k.c:1rx. ~~..0. :{;J

(-b) On Fig. 9.3. draw what Ihe wire mighllook like illhe current in (a) is reversed. [1J

,"-l..

Magcd Louis 4.21 Elcctricity Magnetism22 (a) Fig. 11.1 shows a circuit containinq a lamp and a variable resistor.

June 2003

Fig. 11.1.

The circuit does not work. The lamp does not light and altering the setting on thevariable resistor makes no difference.

In the space below. re-draw the diagram, showing a Circuit in which the variable resistormay be used to change the brightness of the lamp. [2J

(b) Fig. 11.2 shows two resistors and an ammeter connected in series to a 6 V d.c. supply.The resistance of the ammeter·is so small that it can be ignored.

80Q'-----'P

+

Fig. 11.2

(i) Calculate the combined resistance of the 8 nand 4 n resistors in series.

R c. -= K\"," \< L r=.- -g -t- l1 :=. \ '2..

combined resistance = .J..b n [2}

(ii) 1. Calculate the current supplied by the 6 V d.c, supply.

current = D.!.5 A .2. State the value of the current

. t' PO f th Ircuit . fit -.5 AIn sec Ion a e ClrcUi u .

recorded by the ammeter D.·.s..Il .in section SR of the circu.it Q.~'2 P.r. .

[5]

(iii) On Fig. 11.2. show a voltmeter connected to measure the potential diHerenceacross the 4 n resistor. [1 J. '.~

234.22 .Magcd LOllis Elcctt-icity Magnetism

(a). The resistance of a piece of wire at constant diameter depends on .its length.

On the axes of Fig. 7.1. sketch a graph to show how the resistance of the wire varieswith length. (2)

Nov. 2003resistance

O~~------------------~--------o length

Flg.7.1

(b) A reel contains 50 m of insulated wire. The ends of the wire are connected to thecircuit shown in Fig. 7.2, so tfiat the resistance of the wire can be found.

+

meter 1

Fig.7.2

(i) What sort of meter is meter 1? : '" .\.t:~ [1]

(II) Complete the sentence: "Meter 1 is measuring the p.;t .M ~~f.ee~across the coil of wire." [1]

(III) What sort of meter is meter 2? .

(Iv) Complete the sentence: "Meter 2"is measuring thein the coil of wire."

.......................... [1]

J'~s~f1.er.\ \ . . .t.!.f. .[1 )

Maged Louis 4.23 Elcct r icity Magnetism

(v) The dials of the meters are shown in Figs.7.3(a) and 7.3(b).

Fig.7.3(a) Fig.7.3(b)

From the readings, calculate the resistance of the coil of wire.____ t\)

V::;2'4,5 V

1 :2 b3'AR~V/I. -z, -:t,5(03 .=- 3s

/\J /lU

resistance of coil = fl..:? ~ (5)

(vi) What is the resistance per metre of the wire?

- ~e-;;-1u~0~ ')~--~ - 50

. aS JL/mresistance per metre = [2]

24 A. B, C and 0 are an aluminium bar, an unmagnetised iron bar and two bar magnets. Testsare periormed to find out which bar is which.Each row of Fig. 8.1 shows what happens when two of the bars are placed endto end.

June 2004I A I I B I repel \€~.I A I I C I attract

I B I I 0 I no effectFig. 8.1

Which bar is which? Complete the lines below.

Bar A is ag..~ .Bar B Is ~.~ .

Bar Cis : f. ..On :.~ ; .. . Bar 0 is ··..·..···~ · AJ. .m}(}:!J.m .

[4]

4.24 -Maged Louis Electricity Magnetism25 Fig.8.1 shows the view, from above, 01 a sheet of cardboard on top of a bar magnet. The

datted line is the outline 01the bar magnet. Nov_ 2003

®

Fig.8.1

(a) Describe how the pattern of the magnetic field round the bar magnet can be shownexperimentally. If you wish, you may draw on Fig.8.1 as well as write on the linesbelow .

...............bf··p.·btb~....~'()9, ....da ~,pr-c;ki~........ .

::::::::::::::::::::::::Q·:;;~:::::;:i.:;;;;;;·:::pL~:···:J::: ..: :.::::iE::;;;;::;{: ..::::::::..............................................................................................................................................................

.................~ ..rn ~ .. rN.v..k ~&ds. ..d.~ ·..·.·······.....................................................................................................................................................

.........................~.q.J? ~ ~.Jt. ..~{( .y.9..~ .

.............................. d..~e.~ : [4J

(b) State how you would identKy the north pole of the magnet.

....................................b tKe. ..d:!kr.aclifXl.~ tw(hS'5 ..S {hk .····.....·····...........···..f~·&~.lrs~ iJ./~~..p;>'rA5..I5. ..Mr1t.. PI

~kj-ea~.

4.25-N/ia~ed Louis Elcct r iciry Magnetism

26 in a -country where the mains electricity supply is 240 V. the transformer in Fig. 12.1 is usedto enable a 6 V lamp to be lit. N 7003

OV •••

@

B

A

'f----- ,,-.

(a) Calculate the number of turns needed on ihe secondary coil if the lamp is to be lit atnormal brightness.

number of turns » •....2.90...... .... [3]

(b) Without further calculation, state the number of secondary turns needed to light. atnormal briqhtnes s,

A

,

Fig.12.1

\:'VpV5~-c>

2110..=--- :=:6"

(i) two identical 6 V lamps in parallel i.e.

number of turns = .....2 . .....

(ii) two identical 6 V lamps in series i.e.

number of turns e Y. .. .B

[2]

4,26J\1agcd Louis Elccrricity Magnetism

27 (a) One coil of a transformer is connected to a toy train set. The other coil is connected to a240 V a.c. mains supply, as shown in Fig. 10.1.

June 2004

240V f\<J)1---<= I·primary coil._________ _ secondary coil

4800 turns ~~ 200 turns

trainset

Fig. 10.1

(i) How can you tell from Fig. 10.1·that the transformer is a step-down transformer?

..........................it ~ ...l.£.$.~ ±v..r.n.s rx 5.:e.cQflckxry.."'J ......... ..1 [1]

(ii) Calculate the voltage at which the toy train 'operates.

V!/V1 s:- f\J -;t.(t01-

240 / V'- .. =- lt~00 / 'lJ)o .

Vz- ss: ~L{ID y"~t.!)..Q

. <~ ~O()

toy train operates at .1. V [3]

(Hi) 1. The voltage of the mains supply is reduced. What happens to the voltagesupplied to the train set? Tick one box.

increasesdecreasesstays the same

o~o

2. An attempt is made to use the train set in a country where the mains supply is110 V. Suggest one difference that might be noticed in the way the toy trainoperates.

,{( ~ ~...................................... .1 Q w.Qf! .

.............. : ~ { L .. ~ .. f2J

Maged Louis 4.27 Electr-icity Magnetism(b) Fig. 10.2 shows an electromagnetic relay being used to operate an electric motor.

pivoted ironarmature power supply

for motor.----0 0.; .

rI

switch

relay core

Fig.10.2

Below are sentences that describe stages of the process by which the circuit works.'\ •..

A The armature pivots and the contacts close.

B The core of the relay is magnetised.

C The switch is closed and the current flows through the coil.

D A current flows through the motor, making it work.

E The core attracts the top part of the armature.

Put the sentences so that the stages are in the correct order. Put the appropriate lettersin the boxes below. One box has been filled in as an example.

Stage 1 is sentence 0Stage 2 is sentence [[]

Stage 3 is sentence [f]Stage 4 is sentence ~

Stage 5 is sentence 11) I-----------------

[3]

4.28 .Maged Louis Electr-icity Magnetism28 (a) The list below contains the names of five different components that might be found in an

electric circuit. . June 2004

capacitor thermistor variable resistorliqht-dependent resistor resistor

Which of these has

(i) a resistance that falls rapidly when the temperature jises,

............................................~. ;.m..".t .C .

(ii) a resistance that changes when a sliding contact is moved,

.......................................v.:Q:r.1.[A,.~k...... . .r. :h.C , .(iii) a high resistance in the dark but a,.~<?wresistance in daylight?

.....................L15hh:- ..d. peno\.e(Jt ...~S··".s±9.:c···················..········[3i

(b) A lamp shines with full brightness when connected to a 12 V battery, as shown inFig.11.1. ...'. -.---1~-~-11------1

.12V0.50A

lamp.Fig. 11.1

(i) 1. Write down the equation that links resistance with p.d. and current.

Q-VfI2. The current in the lamp is 0.50 A. Calculate the resistance of the lamp.

'R:z V(I_ 1210,S

2- 2. y ..-R-. ..2lt -.n.

resistance of lamp = .[4]..

(ii) A resistor is now connected in series with the lamp, as shown in Fig. 11.2.

r------l r-- -11------112V

1.

lampFig.11.~

State what happens to the current in the lamp when the resistor is added.

. ~.~.c. <•.i'.'~ .

2. Explain your answer.

. .(.+.:- ~

3. Suggest what change might be seen in the lamp .

......:1T B.~.~.......k'.r.tLm r. .[3]

Mazed Louis 4.29 Elcctr'icity Magnetismb

29 Two light conducting balls A and a are hanging side by side, as shown in Fi~.1.

J ~ z Nov. 2004

li~

BJFig. 8_1

A and B are given a series of diiferent charges, as indicated in the table below.In the third column of the table, write what is seen to happen in each case.Use the words repulsion or attraction or nothing. as appropriate.

I .

charge on A charge on B what is seen to happen

positive positive .•.... repl).\S Ian

negative negative-, repvd SYol'/..

positive negative ~cti\on -positive I .oltvuctto f"\zero I

negative zero l a:ttrO-WoY)[5J._---------_ .._----- .

30 (a) Two 10 n resistors are connected in series in a circuit, as shown in Fig.9.1.

Nov. 2004

~

zX 3.0A

Fig.9.1

The current at point X is 3.0 A.

(i) State the current at

1_ point Y, 3.\.Q ..A2. point Z 3.r.Q.A

(il) Calculate the combined resistance 01 the two 10n resistors .

.Ke. =- R \ -4: R•..~ \0 -+ 1'0

combined resistance = Q.. __ n[3J

-. '-, --~------- ...

4.30 . M .Maged Louis Elccrr iciry agnctlsm(b) The 100. resistors are now arranged in parallel, as shown in Fig. 9.2.

I~''''l: f/

.<,

"-r . I

/ •.•. IX 3.0A 1.5 A 100.

r II I

z

Y ion...., ..Fig.9.2

(i) The current at X is adjusted to 3.0 A: The current through one resistor is 1 .5A.

1. What is the current at Y? Tick one box.

OA1.5 A

3.0A4.5A

2. State the value of the current at Z ,}.~.Q A

(ii) What is the combined resistance of the two 10n resistors? Tick one box.

on50.

10n20n

D~DD

[3]-----~ ---------,~..--. -......, .•.--~ ..-.-- .-~ •.•. ,.. -

31 (a) (i) What name do we give to the type of material that allows electrical charges to passthrough it? June 2005 r~

...... ·c. C0 ~J .(ii) Give an example of such a material.

...........................t-::1.eta.Q .( ..QS ~.p~j .(iii) What must be done to this type of material in order to make electrical charges pass

through it? ~

.....:ua.pp~~ ....a.n..:e,.rh,t(0cp..d).:±~

.................~....... n... ·Th.C : .(3)

(b) (i) What name do we give to the type of material that does not allow electricalcharges to pass through it?

.................................

...............................f. .. ~.. ".,,,,"UlYV .c : .

(e)

(ii) Give an example of such a material.

( +i'.................................... p. CA.S .$ .. ~

Which of the two types of material in (a)(i) and (b) (i) may be held in the hand andcharged by friction (e.g. by rubbing with a soft cloth)?

......................................f:rJ:~.~~r. [1J

4.31 .Maged Louis Elccti-icity Magnetism32 . The table below shows the potential difference (p.d.) needed at different times during a day

to cause a current of 0.03 A in aparticular thermistor. June 2005

time of day (24-hour clock) 0900 1200 1500 1800--

p.d./V 15.0 9.9 6.3 7.5

resistance In 500 '330 210 250

(a) Calculate the two values missing from the table. You may use the space below for yourworking. Write your answers in the table.

'R=V/l .= ~%r .s- 3.:?u ~0,03

V= '<;: ss: 2\0 X C).OS = 6,3 t'[3]

(b) On Fig. 6.1, plot the four resistance values.

.resistance I Q

time of day

Fig. 6.1[2J

(e) (i) Draw a smooth curve through your points.

(ii) Why do we draw a smooth .curve rather than a series of straight lines joining thepoints?

........ 5.:.!.S·~·~U\·····I··· ,~r: ..o. ~ h<J.n~ J..fu.Q9[~'t(d) The thermistor is a circuit component with a resistance that decreases as the temperature

increases.

(i) From your graph, estimate the time of day when the' temperature was greatest.

- time of day = ..w.-~~....\.SOO Z \=JOD(ii) State the reason for your answer to (d)(i). l \~OOJ

................it- ~?:t.S ~ t ... .+ v:e..$.J~..fuY.\<R .

........................................................... ·..9~h .[2J

IVln<Jcu Louisb

33 The circuit in Fig. 11.1 is connected up.4.32 Electricity Magnetism

June 2005

0·

resistance wire

Fig. 11.1

(a) How does the ..current in the resistance wire compare with the current in the 2nresistor? Tick one box.

smaller 0 same Iv'I' greaterD [1]

(b) A voltmeter connected across the resistance wire shows the same reading as avoltmeter connected across the 2n resistor.

State the value of the resistance of the resistance wire.

2........................................n [1)

(c) Calculate the combined resistance of the wire and the resistor.

Kc = R, + R-z- 2+2

combined resistance = ~ n [2]

(d) The wire and resistor are disconnected and then reconnected in parallel, as shown inFig.11.2.

resistance wire

Fig.11.2

Maged Louis 4.33 Electricity Magnetism. (i) What is the combined resistance of the'wire and resistor in Fig.l1.2? Tick one box.

zero D1Q 02Q D3Q D

(il) The ammeter in Fig.11.1 reads 0.3 A. What is the reading' on the ammeter inFig. 11.2? Tick one box.

zero Dless than 0.3 A D0.3A D.".

more than 0.3 A 0 -,

[2]

(e) Walls in buildings sometimes develop cracks. The width of a crack can be monitored bymeasuring the resistance of a thin wire stretched across the crack and firmly fixed oneither side of the crack, as iilustrated in Fig. 11.3..

Fig.11.3

The wall moves and the crack widens slightly.

State what happens to

~.... .....c..?~~t.~~)..... (i) th~"length of th~ wire, D.

"(ii) the resistance of the wire .1.0 ~ ..-.-,."" " ........•.[2]

Magcd Louis 4.34 Electricity Magnetism34 . Fig. 6.1 shows a reed relay being used to switch on an electric motor when a variable

resistor is adjusted.Nov. 2005

M+ power_ supply

reed ~relay S

. variable resistor

Fig. 6.1.

{a) The variable resistor is set at its greatest resistance and then switch S is closed. Thereeds in the reed relay do not close when this is done.

(i) State two things that happen in the coil of the reed relay.

~(~~: O.Y+ c. 11. .2 ~.. t~~:R:d.J. a.L ..~nd c ..~.L [2J

(ii} State what happens to the two reeds in the reed relay .

......................." ~9'" ."' d....... . L ~cte.cl _ [1]

(b~ The resistance of the variable resistor is slowly decreased. The reeds in the reed relayclose. Fig. 6.2(a) shows how the current in the coil changes with time.

1 .

tfnurrent I . »-:".

coil O-~-' __ --:--~~

o time

Fig.6.2(a)

currentinmotor Fig.6.2(b}

O~-----L-------- --+timeo

On Fig. 6.2(b), draw a line that might show how the current in the motor changes withtime as the variable resistor is adjusted. [4]

_. ----.---

Mugcd Louis 4.35 Electricity Magnetism35' (a) Two magnets are laid on a bench. End A of an unidentified rod is held in turn above

one end of. each magnet, with the results shown in Fig.8.1.Nov. 2005

\D

Fig.8.1

(i) Suggest what the unidentified rod is made from.

t> '" ".- .A "I (l!:) J(ii) ~~~~~..~~~~, i;1~:~,~a;~~~~~n't~~~~~d~\~ld ~;e';'~~~'en~ ...:..... [1J

1. an unmagnetised iron bar, p. 51hAn..3 .(.in...ca..s;e U W()'\e I'rtly

2. an uncharged plastic rod. . ,..... >th~ . [2]..(b) Fig.8.2 shows four identical plotting compasses piaped around a bar magnet where

the magnetic field of the surroundings can be ignored. The pointer has only beendrawn on one plotting compass.

....

88 I S N I 8

8 ..".

Fig. 8.2

On F.ig.8.2. draw the pointers on the other three plotting compasses to indicate thedirections of the magnetic field of the bar magnet in those three places. [3J

Magcd Louis 4.36 . Elcc{r-icity lVlagnctism36 {a) Fig. 9.1 shows five circuit symbols and their names. The names are in the wrong order.

Draw a straight line from each symbol to its name. One line has been drawn as anexample.

cell

Nov. 2005

lamp

ammeter

voltmeter

switch

'·Fig.9.1

(b) Fig. 9.2 shows a circuit.

ammeter 1

Fig.9.2(i) In the space below, draw the circuit using circuit symbols. [1]

(ii) On your diagram in (b)(i). add a voltmeter connected to measure the potentialdifference across the cell. . [1]

(iii) When the switch is pressed so that the contacts join. which of the lamps light up?

...............................................~.9.~ [1]

(iv) When there is a current in the circuit. ammeter 1 reads 0.5 A.

What current does ammeter 2 read?

current = ..Q.~.5. A [1)

(v) One lamp "blows". so that its filament breaks.

What happens in the circuit?

......................................~.r..~nt ?.±O~ : ..... ...•................... [1]·

Magcd Louis 4.37 Electricity Magnetism37 (a) State wh.at is meant by the north pole of a magnet.

June 2006.kv.I..cb .

Wt1atsort of force, if any, is there between the poles? Tick one box.

attractive Drepulsive [2]no force D (1]

(c) Fig.8.1 showsthe north pole of a magnet close to an iron bar.

"'Vl _. I" . r magnet

I N I~i:a~

WFig, 8.1

(i) The iron bar is attracted to the north pole because of induced magnetism in theiron bar.

On Fig. 8.1, mark clearly the induced north pole and the induced south pole of theiron bar. (1]

(ii) State what happens to the induced magnetism in the iron bar when the magnet istaken away.

....................d.t~p. _<I.\r.5 (..i.XQY.':- L$. ~ .Q±.t..Mfl3~f::). (1)--------~-----------

Magcd LOllis 4.38 Elcctriciry Magne{is/ll38 . In the boxes of the left column below are some electrical hazards. In the boxes of the right

column are means of protecting against those hazards. June 2006 ~

From each hazard, draw a line to the appropriate protection. One line has been drawn as anexample.

-electrtcal hazard means of protection

visual check of cablesbefore connecting appliance

loose live wire touchesmetal case of appliance

fuse or circuit-breakerin the circuit

worn insulation on cableto an appliance

use of switches witha nylon pull-cord

steam in a washroomcondenses inside a switch

earth wire connected to themetal case of the appliance

wires get hot becausecurrent is too high

[3]------------------_._---_. __ .. -" ..•-. _ .. ---10 A person has a 6 V bell. He hopes to operate the bell from a 240 V a.c. mains supply, with'

the help of [he transformer shown in Fig. 10.1. .,-----,

240Va.c. <:input

Nov. 2006

(\~output

primary coil secondary coil5000 turns 250 turns

Fig. 10.1(a) State how you can tell from Fig. 10.1 that the transformer is a step-down transformer.

..............f.t :~~ ....l~5. tv015. ..or1... : CP...~CJ.r:y..... .i.£. (1] .

(b) State how the output voltage compares with the input voltage in a step-down tr~sformer .

.........................v.~.I~ r5. ..leJJ.. (11,

(c) Calculate the output voltage of the transformer when connected to the 240 V mainssupply. \ .

V,- s:V"L,

2L<OV2

I/'--h ..5(,)00

s;:. --250

output voltage = .\.Z- : V (3)

(d) Why would it not be wise for the person to connect the 6 V bell to this output?

.............................v.Q..\tP..¥ .i.L ..~..... 8.k ~ :..

....... be.LL W~Jo.! h da.m.a~." : [1]----- .~-.-.------~.--- ._. __ .__ ~ _0- . ....

•4.391Vlagcd LOllis

39 . (a) Fig.8.1 shows two groups of materials.Electricity Magnetism

Nov. 2006

GROUP 1 GROUP 2

. copper plasticsiron silk

glassaluminium ebonite

Fig. 8.1

(i) Which group contains metals?

................................C .. p..... J-

(ii) Which group contains insulators?

.'~....

{Hi} Write down the name of one of the eight materials above that may be charged byrubbing it with a suitable drvcloth. .

....: p.f.o..s.:H Cd. .(3J

(b) Two charged metal balls are placed close to a positively-charged metal plate.

One is attracted to the plate and one is repelled.

chargedplate

_ repelled by plate

~s\~

v~v-..-·_ attracted to plate

Fig. 8.2II

Write a + sign on the ball that is ~os!tively charged and a - sign on the one that isnegatively charged. '. [1]

(c) State what is meant by an electric field.

................................ .1~Qn.... {Qtjn.d o...... J1ta~ .

.........................0(~ .r".t. €!.x..p.?!Cu:~Y.l. ..? Y.f.fQ..cc.e._ =~::_~

•

4.40Magcd Louis

Fig. 12.1 shows an electric clrcult.40. ~~=-_ Electricity Magnetism

Nov. 2006

Fig.12.1(a) The lamp lights, but the ammeter needle moves the wrong way.

What change should be made so that the ammeter works correctly?

...................re . ("'S , .r.1J.).ed.i?(L ~ aY.Y.lm0.DK:-. (1], or e~erv{

(b) What does an ammeter measure? (

..... ...._...._...........G .aed:.J,J~;1,~Amperes [1]

(c) In the space below, draw a circuit diagram of the circuit In Fig. 12.1, usinq correct circuit.

symbols. f® -1r ~ [2]

(d) (I) Name the instrument that would be needed to measure the potential difference'(p.d.) across the 15 n resistor .

..... VO.[ tft.1eJe.r. .(il) Using the correct symbol, add this instrument to your circuit diagram in (c), in a

position to measure the p.d. across the 15 n resistor.(e) The potential difference across the 15 n resistor is 6 V. (2]

Calculate the current in the resistor.

. 1=VIR. -= 6/15 current = O'!..4. A (3]

(t) Without any further calculation, state the value of the current in the lamp.

lamp current = ....o..~.~.....A (1]

(9) .A:not~er 15 Q resistor is connected in parallel with the 15 Q resistor that Is already in thecrrcuit.

(i) What is the combined resistance of the two 15 Q re~istors in parallel?

Tick one box.

30Q D15Q D7.5Q 0zero ~

(ii) State what effect, if any, adding this extra resistor has on the current in the lamp .

......................rYJ.~.~k ili~t .[2)

.•.

4.41Mngcd LOllis Elcctl·icity Magnetism

.41 (a) Fig. 9.1 shows tworesers connectedto a 6: :attery. June 200~

I6V I

1 10Q

---'----'-t--·----oo X

C sliding.contact

/

I6V I ~----oX

. (i)

IL--'. _~B_()y

Fig. 9.2 . . .State the potential difference between X and Y when the sliding contact IS at

......b.....'V1. end A of the resistor,

2. end B of the resistor. ......0.....V [2J

(ii) The sliding contact of the resistor AB is moved so that .the potential differencebetween X and Y is 5 V.

On Fig. 9.2, mark with the letter C the position of the sliding contact. [1J

Fig. 9.1(i) What name do we use to describe this way of connecting resistors?

...........................,: e..?............. .Y.: pote.-nh~q.J...d..\yl'd.@C [1]

(ii) Calculate the combined resistance of the two resistors.

Rc.. = R\ -t-R 2 =- IO-t-2.

.. combined resistance = .. ) ..2.:.: ..... .Q [1]

[Total: 12J

(i ii)

(iv)I

Calculate the current in the circuit.

J - VA<~ G 11'2 current = ....Q.fS....A:.. [4]

Us~ your answer to (a)(iii) to calculate the potential difference across the 10.0resistor. V.=. 1- X R

-=0. ') 'X' \-0 =- 5V potential difference == ••••• 5 V [2J

(v) State the potential difference between terminals X and Y:

s.................. V [1]- _ ...._---:--. . .....- ....~-.-.. -. . .... -.- ---

,..4.42Magel! Louis Electricity Magnetism

42 Your teacher gives you a length of wire, a sensitive millivoltmeter and a powerful magnet. Youare asked to demonstrate the induction of an e.m.f. in the wire.

(a) Describe what you would do.

···..·················C·.()(.l.eof ....

June 2007 r\::l\OJ

.e.eo.5.S ...1. ...m.1~{.u.vo.lfn1der•..ce. ........................... , .

... mQ..V!? w.i.ff. a.CmJJ. ..JM~tLdrC: ...8.td.J. .

.......................;..cp.(., Q1 ~ «: rnqg.'6d. ..p.q.$.f. ..W.f~) .

.................................................. : [2)

(b) How would you know that an e.m.f. has been induced?

.................................mJl/i. .. ftm.e.flf.:: d~P.f.e.d'.5 [1)

(c) Name a device which makesuse of electromagnetic induction.".

··..·· · · ·..·9·e.:JJ·e '''. .c [1)

[Total: 4)

Fuses me often included in circuits.June 2008..

(a) In the space below, draw the circuit symbol for a fuse.

-l r--(b) Ih' . • [1], dnen the statements In the boxes below are put In the correct order, they describe how

a fuse protects a circuit.

A

fuse wire heats upBcircuit is broken,so current stops

Cfuse wire melts

Dcurrent becomestoo high

On the line below, list the letters of the four boxes in the correct order .

....................................D. A C B. · : (2)- - - --- -

(c) By mistake, a fuse with too high a rated value is put in the fuse-holder in a circuit.

~/

State two possible outcomes of this mistake.

i · ±O'Q 8.reo.Vt ONrTe.,a OJJ8hf..fL~nN .2 £Us.:e ..m&bf J1.rt md): [2J

. App'ltcmca- LMfgh1 he dam@9eJ_ [Total:5J

4.43·Magcd Louis Electricity Magnetism44 Fig. 1.1.1 shows a bar magnet on a board in a region where the magnetic field of the

surroundings is so weak it can be ignored. The letters Nand S show the positions of thenorth and south poles of the magnet. Also on the diagram are marked four dots. Q

r---------.--- Jnne 2007 \ \~

. Fig. 11.1

(a) On Fig. 11.1, carefully draw four magnetic field lines, 'one passing through each of thefour dots. The lines you draw should begin and end either on the magnet or at the edgeof the board. [5]

(b) On one of your lines, put an arrow to show the direction of the magnetic field. [1]

[Tota!: 6]

---.--------------------------------------~~ j

-:

4.44 .M~ged Louis Elccrr iciry Magnetism45 . A thermistor connected to a variable voltage supply is immersed in a beaker of water.

The beaker of water is heated slowly, using a Bunsen burner, as shown in Fig. 9.1.

Nov. 2007variable voltage supply

r----{)~o-----,

A

thermometer --------

water

Fig. 9.1

At different temperatures, ·the voltage is adjusted until the current is 25 mA and the value ofthe voltage is noted.

The results are shown below ...

ternperatura/vtj 15 30 45 60 75 90

voltage/V 18.8 8.8 4.7 2.6 1.5 1.2

(a) On the axes of Fig. 9.2, shown on page 13, plot a graph of voltage against temperature.[4]

'-

Magcd Louis

25

4.45 ElcctriciryMugnctism

valtagelV

20

10 -

5

oo 80 10020 40 60

temperature 1°C

Fig. 9.2

(b) From the graph, find the voltage needed to give a current of 25 mA

(i) at 40°C, voltage needed = ..~ .•3 (5.~7.) b.d V [1]

(ii) at 80°C. voltage needed = ~/L...(:\.~.~)J:.1. V [1]

(c) Use your results in (b) to calculate the resistance of the thermistor

(i) at 40°C, 'Kz:-V/I 'St"T_.Q5 X'Ia-1-

resistance at 40°C = ~.~O ::::::-=-: ..2~O ::-''""L.~

(ii) at 80°C.'}?2- V/1

..rresistance at 80°C = ~.O..~ 6.0 0

[5]

(d) Use your results in (c) to complete the following sentence about thermistors of the sortused in this experiment.

The thermistor in this experiment is a device whose resistance de.cr:-eCt5.e5 ..as the temperature increases. [1]

...-.-------

Magcu Louis 4.46 Electl-icity·Magnetism46 .A Gail of insulated wire ls connected in series with a battery, a resistor and a switch.

Nov. 2007

~ ®r-~t--'!I--~---j

L----..",,--...,,-.....,,-..... __....r ....,,-.....~---,....-J

Fig. 10.1,,~...

(a) The switch is closed and the current in the coil creates a magnetic.field.

(0 On Fig. 10.1, draw the. shape of the' magnetic field, both inside and outside the coil.{4]

(if) A glass bar, an iron bar and a perspex bar are placed in turn inside the coil.

Which one makes the field stronger? tr.0.n 9Qr [1]

(b) Two thin iron rods.are placed inside the. coil as shown in Fig. 10.2. The switch is thenclosed.

~ I,----1 - - -I ---...:...

AA AA

v v

Fig. 10.2

The iron rods move.apart. Suggest why this happens .

........................r.o..d.s. he..c~~ rnf3jJ.ehSed .

..........................l.o..o..fh...wf.II ...&.Y.~ ~,r.n~ ..dlr.f.clt~n..(N;.31.{3]

<:, ~ ~-6aclLO TF\Qf- [Total: 81----------.:c:.-,7.-L--I~'4--~~r-. . - ---.-.----- -----...---

Magcd Louis 4A8 Electricity.Magnetism

LI8 . (a) An experimenter uses a length of wire ABC in an attempt to demonstrateelectromagnetic induction. The wire is connected to a sensitive millivoltmeter G.

June 2008

G

---~Fig. 11.1

Using the arrangement in Fig. 11.1, the experimenter finds that she does not obtain theexpected deflection on G when she moves the wire ABC down through the magneticfield.

.,(i) Explain why there is no deflection shown on G.

..•................... Y.1 CU.~t ....lf\..... !.r.CW.t .......... .'lfl1.-..£~ ..t.rJ.dM.ce.J tn. A.~ r.5. : .

. Ctal). .J.(eJ ?J e.~.m:~.t~..: i.'().~ad. i.r).. B.C..[2]

(ii) What change should be made in order to observe a deflection on G?

.............................Ro.±o1e. A.B. ..c ..,- (o.f:\ ..;..fs...aX.fiJ. .

..............~.~ S.tr.a{Jh±i:7 Q.~.t A.B ..C [1]

(b) Name one device that makes useot electromagnetic induction .

........: ~.IYarlS.:P.o.CrtJ.er Qr:...'3U1e.rato.C : [1]

---------_1 [Total: 4)

~ ('Ylcorrecl' answers a-; ~5"----

-tqKe olJJ:of you.~mQYK~ ...•.

~,

4.49' -Maged Louis Electricity ,Mngnctism49 ,(a) An iron rod is placed next to a bar magnet, as shown in Fig. 8.1.

IN ,- sl IN sl Nov. 2008, Fig. 8.1 iron rod

0) On Fig. 8.1, mark clearly the north pole and the south pole that are induced in theiron rod. "-'" [1J

(ii) What happens to the magnet and the rod? Tick one box.

nothi~; --- 0they attract IVi

they repel 0 [1)

(b) A 'secori'dbar magnet is now placed nexlt~'the iron rod, as shown in Fig. 8.2.-'

L!l ---'s I IN sl• M_ --- -. •• - • _ •• ~ iron rod

. "Fig. 8.2 .(i) On FIg. 8.2, mark ciearly.the magnetic poles induced in the iron rod. [1)

(ii) , What happens to the iron rod and the second maqnet? Tick one box,

nothing 0they attract I vi'

they repel 0 [1J(c) The iron rodis-~emcwed, leaving the two magneis~'as-shown in Fig. 8.3.

sl

sl slFig. 8.3

What happens to the two magnets? Tick one box.

nothing 0they attract Iv Ithey repel 0 [1J

(d) The second magnet is removed and replaced by a charged plastic rod, as shown inFig. 8.4.

sl 1_+ -1 ""charged

plastic rod

Fig. 8.4

What happens to the magnet and the plastic rod? Tick one box.

nothing .>they attract 0

they repel 0 [1)-'

[Total: 6)

4.50·'Magcd Louis Elcctdcity Magnetism50 A toymaker wires a 'circuit in a toy house, so that a 6V lamp can be switched on using either

switch 1 at the bottom of the stairs or switch 2 at the top of the stairs.The circuit is shown in Fig. 9.1.

X Y

~----'---L>-mv""'p---------S-W-i-tC-h-2-~

a

Nov. 2008

6V supply

switch 1

Fig. 9.1(a) When switch 1 is in position A, what is the position of switch 2 so that the lamp is lit?

...................................... ....: : :~~·.: C1.................................. [1]

(b) When switch 2 is in position b, what is the position of 'switch 1so that the lamp is lit?

(c) Tile lamp has a resistance of 4.0Q.

.......................................................................................B [1J

CcfdzJ l~ntaJ\ .f1 =V IR

..::::E'ILi- \. '5

Calculate' the current in the circuit.

. - - . .. - . current = I..~..5. A:................. [4J(d) The toymaker decides he wants to have two 6V lamps in the circuit with the 6V supply.

Which of the fol/owing means of connecting the lamps between X and Y, shown inFig. 9.2, is the best? Give two reasons for your answer. -,0-

X Y X Y .---0

connection 1 .. connection 2Fig. 9.2

Which is best? : c..0.!\~..~-b~ :2.. .Reason 1 •....................... f.t.d( VQ1+.~ (At\( br 'jhtn.o).Reason 2 tt Cf.k..~.s:: ../s:J..J1chll9r~~1'}~iO([~

. . '(Total: 9J--_._---

4.51 ..Maged Louis Electricity Magnetism

51 The circuit in Fig. 10.1 shows an electromagnetic relay being used to switch an electric motoron and off. The relay coil has a much qreater resistance than the potential divider.

pivoted iron Nov. 2008armature G\ ~power supply

for motorI-~O6V •

r~~iswitch / motor

relay core. contacts- Fig. to.t

(a) The relay operates when there is a potential difference of 3V across the coil.On Fig. 10.1, mark the position of the slider of the potential divider when the relay justoperates. [1]

(b) Describe how the relay closes the contacts in the motor circuit.

.........................~ CL\(~n.t ir.l. C·ci.l. , ; .

... c;;: Catt r:r.t:t ~ ..Mt.t sd .

........................... a.r.~~ cill.rn.(t d .

.: ct.on:t?l:h\~ p l\cP.t.$. : .·· ·..··..···..· @ ar.tfIOl-urc. pu.shes. cCn.tqd..? C..\~~d.. (3]

52 Fig. 11.1 shows a transformer being used to operate a 6V lamp from a 240V mains supply.

Nov. 2008

\\\~

[Total: 4J

6Vlamp

A

240Vmains

B

8000 turns Fig. 1t.t iron(a) What name is given to the piece of iron that links the two coils?

....·..· Co.cy [lJ

(b) For the transformer to operate, must the mains, supply be a.c., d.c., or doesn't itmatter?

···· ·· ·..··..·· QJ c.~.............................. (1J

(c) Using the information on Fig. 11.1, calculate the number of turns on the secondary coil.

v'p PV.?.-> Ns number of turns = SO.C............. [3J

--- ._-_._---------_._._---_ .._-------_._-_. __ ._---

(d) State why it would not be wise to connect a.1.5V.lamp between A and B.

.:..: ~..tt-~ ..fcC ~l~~\ !..JJ?lIwp ..\t . '1\.. ..kl~bJ [lJ

[Total: .6J

Magcd Louis

53 .(a) Four rods are shown in FIg. 8.1.

4.52"Elcc n-iciry Magnetism

June 2009

®

plastic rod iron rod .. wooden rod brass rodFig. 8.1

State which of these could be held in the hand at one end and be

(i) magnetised by strokinq itwith a magnet,,IrOr"L. [1)

(ii) charged by stroking it with a dry cloth.

. plt;tS.tl~ [1)

magnet A magnet BFi9·8.2

The north pole has been labelled on magnet A.

On Fig. 8.2, label the other three poles.(c) .. Chargecf rods-C-ind 0 in Fig. 8.3 are ariractln-g' each other.·

[1]

L__ +Irod C

i rodO--Fig. 8.3

On Fig. 8.3, show the charge on rod O. [1]

(d) Fig. ~A §hows a plotting compass with its needle pointing north.N(Dt

Fig. 8.4 I

A brass rod is positioned in an east-west direction. A plotting compass is put at eachend of the brass rod, as shown in Fig. 8.5. ,

plotting

compass ----m__ 7 __ 1 CD

brass rod

/N

tFig. 8.5

On Fig. 8.5, mark the position of the pointer on each of the two plotting compasses. [2)

[Tota!: 6]

Magcd Louis'54 Fig. 9.1 shows a simple circuit.

4.53-Electricity Magnetism

reading50mA

June 2009

R

(a) What is the value of

(i) the e.m.f. of the battery,

Fig: 9.1

. [1J

(ii) the current in the circuit?

......~: (0. ~.:V [1J

(b) Calculate the resistance R of the resistor.

f< = VII6?O.OSfT R= ..f2..D. :J:L .. [3J

(c) State how the circuit could be changed to

(i) halve the current in the circuit,

........................... ..i. . .c£(aS£.....C.~5.l.J:WlJ. .....(.ci.y.b.};0. ..I.1j.... [2]

(ii) reduce the current to zero .

............................ .. :.-J? ~~"'\ Q ..C '.t. ('(f(. K h'::ze .:)1J(d) A student wishes to include a switt;tr'1n the circuit. but misiakenly connects It as shown

in Fig. 9.2.6V

r---j~--11---------,studeQi'sincorrect

connection

'-------.....-1'-_R_~

. Fig. 9.2(i) Comment on the size of the current in the circuit if the student closes the switch.

············· V ~ &~ .(...in.±if.,' ..t:J [1]

(ii) What effect would this current have on the circuit?

.••.•.••...•.•...•.....•...•. -.~ .•:;). • .1". • ~.-r.:~ .................................... ~ :I.. ~f:..r.::; -::-:..Q.ve ~c.ts: ....................................~~1 ~OV.e.r..~td.L........................[2]

!Total: 11]

'.

Maged Louis 4.54 Electricity Magnetism

55 The apparatus in Fig. 10.1 is called a force-an-conductor balance. When there is an electriccurrent J as shown in XY, there is a force on XY that pulls it down. This force is measured byputting weights in the pan until XY is brought back to its original position.

Ju·ne 2009

pan

currentin

-.

Fig. 10.1

(a) Statewhat would happen if the current direction were from Y to X. . . _,

Y I ~ L' l{ VtOiA)(}..........X ~'O.w.. \ t:c.\.:Y.~ V.{.. ';':.(,. nr.i.<:. . i.y.{.\J~../~.n..mq~ [1]

(b) An experimenter uses the balance to determine the force Fon XY for different currents I.His results are given below..

J/A 0 0.5 1.0 1.5 2.0

FIN 0 0.012 0.023 0.035 0.047

(i) On the grid of Fig. 10.2,

1. mark suitable scales to plot a graph of FI N against II A for these values, [2]

2. plot the points on your grid, [2J

3. draw the best straight line through your points. [1]

Maged Louis4.55·

Elcctriciry Magnetism

+-::-l I -

TlI I

I II

-. ::--1 __::-1-II++ -+

iT TI

.w.... .;-1+- - ±~--- -l 1-- -- 1

'TT"T" + -I - . iI

FIN

I'.. I

i I I

+t-l--I I I

!+r--'ITI

I i I i I

_ _ J. •.

- II -~::I~I:;:::'- :r~:'~__.:~:<:,~Ir-' - -r ---r- -..- -r-

. "I 'T'-

o.os

++I II I I

I

-rr+-.=i=!-I I

0,0'

I

./- -.1 _ _ _I+ : --iI ! I I _II I ! I '-1:- =1= -t-tt ±lit - ':rt +++- .,-

O~l~~~~I-I~~j~~t:·-il~[±~i~~TI~~~r--iI~i~ii'-~I~-~~·~Ft~-~~:~:ilil~~-~--~-~·i-~-~·il~:~=I·~·~~t~'l-~-i~=~-.~=r-~-:~-~:~=~:~:l:~:''/ - I I , I i+- - : : -lHH'++'--f-t::d- .J-'±. -- :-_., f-JA'- H- ~Ii -+ -! -1-1_+ --::r ---

I, I I I

I I I J ,: tti rl--i---1 : ; I: I I -f-H- - H- + -1-' ._j-

Y I 1 II I I I I I I i f I

-i::H, ~_. ~ f-H:j- - ~r-i- :1-. -, I I 1 I ,I. . , I I I

i ! I I I I I _ I

~t+t-t-"l!HIA-Ff'+-t$t-::~ -1'1- ~ T ft .r;~~::I-~_fjt- = -1] al,'-t-'rlt-·-.t+,.r-+--I~-t~----1--11-' 11 :: -- _IT .-I--I:-::L¥:ij=l-r:L :P-f - ~tE\-~t -t-H- H-t--FFF rr- ----~I-·----·--h---n+--I---l-l-1

I I I I I I i l

I I

rtI I

l-I,

I._ ...l

l-i I

I I I

, ,I

"i

--I-,

I , I"

i -++r --I .-"- 1-:H-l-H--i+-·+ -, -HlH-+ i+i+H+ ·1++-', -.+. - 1Ti'r! tr -t-t'h-i ++-j~)

)

\I'

Q ~..- JIA

Fig. 10.2

(ii) From your graph, find the force on XY when the current is 1.6A.

force = 01..0 .6~ N [1]

(c) Name one common device that uses the effect demonstrated by the force-an-conductorbalance .

. MQtQ..r. .(...?~ .'. ~ - ~ ~_ [1]

;""'G?/.Jr'/o~--4l-U.u...lfJ1,~~.-2'.'s)--.-..._._rT~~al_:8_1_

,..

Magctl Louis 4.56 Elcctr icity Magnetism56 (a) The two circuits shown in Fig. 9.1 each contain two resistors and a battery.

Nov. 2009Complete the statement under each circuit.

-rI

. II'

• "T'"III

Resistors R1 and R2 are Resistors R3 and R4 are

connected in ~e.K:t~~ ;:... co~nected in p..0.C6!:Jle.J. .Fig. 9.1 .

(b) A student connects the circuit shown in Fig. 9.2. The resistance of the 12V battery is solow that It ~?n be ignored. ;:..,......_--"--"='

12V-rIII

2800

.-----QA

2000

~-----~-------DBFig: 9.2

€i) Calculate the total resistance in the circuit.

'~!2- '1.8'0 ;200

[1]

resistance = A~.Q Q [21

.(ii) ..Calculate the current 'delivered by the battery.

I::: *c '7r:~ _ 0·025current _ [4]

(iii) Calculate the potential difference (p.d.) across. the 200Q resistor.

V-:2... ~~R-= 002SX2o:J p.d.= .. V [2]

(iv) Describe how the student could check whether the p.d. across the 200Q resistor isthe same as you have calculated. Include the name of the instrument he would usefor this. .

•••••••••••••••••••••••••••••••• I_....::J.r.LtI~~•• ' ••••••••••••• (±~ ; .. .. ..' .1.1- C: {3 .....................................

............................................................................................................................ [2]'

[Total: 11]

Maged Louis

.57 Fig.10.1 is a diagram of a transformer.

4.57Electricity Magnetism

300 turns30 turns

12Va.c.

Nov. 2009

."-' .a.c. voltmeter

core-Flg•.10.1

(a) (I) On Fig. 10.1, clearly label. the core of the transformer. [1}

(iI) Name a suitable material from which the core could be made., 0

..................................... ~ .. . \..... .. [1]

(iii) State the purpose of the core .

...............~ ::-fR ~ maJ ..(b) Calculate the reading on the voltmeter.

:21:\. ..: [1:

~ ~ tJ,V2-. 'f'I;.12 _~

-V2 - 300

voltmeter reading = ..1.2...0 V [3

[Total: 6

r .\

4.58'Maged Louis Electricity Magnetism. .

58 A woodworker buys an old electric drill that has been used before, The drill is illustrated inFig. 11.1.

Nov. 2009

-, Flg.11.1

The drill mechanism itself is guaranteed to be electrically safe.

Suggest three.checks the woodworker could make in order to ensure that the rest of hispurchase is electrically safe.

1 . . ..p. ..:. .. '.'r.e,5. .

. . r. .v.l .. ?.uL ... ,2 , Y.:l ~9.. .. w.:~ , ..............................•.....•................ \).1.Q..-.: b.Q .'(.'t...... f~t~ .3 ~ p.1. . .0 .":J W.f\... at ......................................•...................................................................................................... [3)

(Total:3J