electricity and magnetism q unit 4.rtf

7/25/2019 electricity and magnetism q unit 4.rtf

1/27

1. The diagram shows two charged spheres X and Y, of masses 2m and m respectively, which are

just prevented from falling under gravity by the uniform electric field between the two parallel

plates.

X Y

Which of the following is a property of a uniform electric field?

A The field strength is the same at all points.

B The field acts eually in all directions.

C The field produces no force on a stationary charged particle.

D The field produces a force on a moving charged particle which is always perpendicular to

its direction of travel.(Total 1 mark)

2. !a" # 22$$ %& capacitor is charged to a potential difference of '2 ( and then discharged

through an electric motor. The motor lifts a )$ g mass through a height of 2* cm.

(i) Show that the energy stored in the capacitor is approximately 0.16 J.

Energy = ..........................................

(2)

(ii) What is the efficiency of the electric motor in this sitation!

Efficiency = .....................................(2)

Ashlyns school 1


2/27

(") #he capacitor is charged to 1$ % again and then discharged throgh a 16 Wresistor.

(i) Show that the time constant for this discharge is approximately &' ms.

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(1)

(ii) Setch a graph of crrent against time for this discharge on the grid "elow.o shold indicate the crrent at t = 0 and t = &' ms.

' 2 $

' $ $

+ $

, $

* $

2 $

$

m

#

$ 2 $ * $ , $ + $ ' $ $m s

(3)

Ashlyns school 2


3/27

(c) *apacitors are sed in adio systems when connecting the amplifier to thelodspeaer.+n one sch circit the capacitor has a ,ale of $$00 m- and the lodspeaer hasa resistance of 16 W.

2 2 $ $ &

' ,

(i) #he lodspeaer prodces longitdinal wa,es. What is meant "ylongitdinal in this context!

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(2)

(ii) +deally the time constant for sch a circit shold "e mch greater than thetime period of the lowest fre/ency note. iscss the extent to which thiscircit wold "e effecti,e if the lowest fre/ency note is $0 2.

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Ashlyns school 3


4/27

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(2)(Total 12 marks)

Ashlyns school 4


5/27

3. 3 simplified diagram of a cathode ray oscilloscope is shown.

- l e c t r o n g u n s y s t e m

a t h o d e # n o d e

- l e c t r o n b e a m

( a c u u m

/ i g h t

0 h o s p h o r

c o a t i n g

1 c r e e n

(a) Electrons li"erated from the cathode are accelerated to the anode throgh alarge potential difference gi,ing each electron in the "eam an energy of 1.$ e%.

(i) *alclate the ,elocity of electrons in the "eam.

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%elocity = .......................................(3)

(ii) #he phosphor coating prodces green light each photon of which has anenergy of $.4 e%. #he efficiency of the con,ersion of electron inetic energyto light in the phosphor is 5.0. *alclate the nm"er of photons that will"e li"erated from the phosphor coating "y the arri,al of one electron in the"eam.

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Ashlyns school 5


6/27

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7m"er of photons = ....................(2)

(") +n a "adly8designed cathode ray t"e electrons arri,ing at the screen are notcondcted away "t "ild p in the area where the "eam hits it. Explain how thiswill ha,e an ad,erse effect on the amont of light emitted "y the phosphor. omay "e awarded a mar for the clarity of yor answer.

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(4)

(Total 9 marks)

4. 3 capacitor *1is connected to a spply. When a potential difference of 4.0 % is applied

across the capacitor it stores a charge of 0.50 n*.

Ashlyns school 6


7/27

* . $ ('

(a) (i) *alclate the electrical wor done "y the spply as it transfers this charge.

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Wor done = ....................................

(2)

Ashlyns school 7


8/27

(ii) 9ar on the diagram a"o,e the magnitdes and polarities of the chargesstored on the plates of the capacitor.

(1)

(") 3 graph of charge stored against potential difference across the capacitor isshown.

h a r g e s t o r e d o n n

$ . +

$ . ,

$ . *

$ . 2

$ . $

$ ' . $ 2 . $ 3 . $ * . $ 0 o t e n t i a l d i f f e r e n c e (

'

Explain how this graph spports the fact that the charged capacitor is storing 1.6nJ of energy.

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(2)

(c) With capacitor *1charged to 4.0 % the spply is remo,ed and a second

ncharged capacitor *$is connected in its place as shown.

' 2

*apacitor *1transfers some of its charge to the plates of capacitor *$. 3s a

reslt the potential difference across *1falls to &.0 %.

Ashlyns school 8


9/27

(i) :y referring to the graph for capacitor *1 dedce how mch charge

transfers to capacitor *$.

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*harge transferred to *$= .................................

(1)

(ii) ;n the grid "elow show how the charge stored on capacitor *$,aries with

potential difference dring this charge transfer process.

h a r g e s t o r e d o n n

$ . +

$ . ,

$ . *

$ . 2

$ . $

$ ' . $ 2 . $ 3 . $ * . $ 0 o t e n t i a l d i f f e r e n c e (

2

(2)

(iii)


10/27

Ashlyns school 10


11/27

5. 3 small 4search coil5, connected to a data6logger, is used to investigate a steady magnetic field.The coil is placed so that the field is perpendicular to the plane of the coil. The coil is then

turned through 7$8 in *$ ms, finishing with its plane parallel to the field. This induces an e.m.f.

across the ends of the coil.

The data6logger indicates that the mean ,ale of the e.m.f. dring the process is 0.1$ %.

+t also displays the following trace.

$

$ ' $ 2 $ 3 $ * $

T i m e m s

- . m . f . (

(a) 3dd an appropriate scale to the ,ertical axis on the graph a"o,e.(1)

(") #he search coil has '000 trns.

(i) #he mean e.m.f. indced dring the rotation is 0.1$ %. Show that themagnetic flx throgh the coil "efore rotation was approximately 1 %Wb.

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(2)

Ashlyns school 11


12/27

(ii) #he coil has a diameter of 1.0 cm. *alclate the magnetic flx density ofthe magnetic field in which the coil is rotated.

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9agnetic flx density = .....................................(2)

(Total 5 marks)

6. #he photograph shows a flexi"le copper wire attached to the terminals of a dry cell.3 strong circlar magnet 1$ mm in diameter is attached to the side of the cell. #heinteraction "etween the crrent in the wire and the magnetic field of the magnet casesthe wire to le,itate.

Ashlyns school 12


13/27

#he diagram shows the arrangement ,iewed from a"o,e.

1 9

:

9 ; T T ;

1 # / -

(a) raw on the diagram the magnetic field prodced "y the magnet.(2)

(") #he following measrements were made

pward force on wire = 5.0 < '$=3

7

crrent in wire = '.5 3

length of wire in magnetic field = 1$mm

(i) Show that the magnetic flx density is a"ot 0.1 #.

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(2)

(ii) State one assmption yo made in yor calclation.

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Ashlyns school 13


14/27

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(1)

Ashlyns school 14


15/27

(c) #he manfactrer5s data sheet supplied with the magnets gives a value of $.3 T for themagnetic flu> density. 1uggest a reason why this is different from the value given in !b"

!i".

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....(1)

(d) Explain what wold happen to the wire in the following arrangement.

9 1

=

:

9 ; T T ;

1 # / -

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....(2)

(Total 8 marks)

Ashlyns school 15


16/27

Ashlyns school 16


17/27


18/27

(ii) Explain yor answer to (c)(i).

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(2)

(Total 8 marks)

8. 3 s/are rigid metal frame ?@AS of side 1$ cm forms a closed circit with anammeter.

#he area enclosed "y the dotted line is a region of niform magnetic field of flx density

$.0 < '$=2

#. #he field is confined to this area and directed into the page.

# B0

C1

0 ; 1 D T D ; 9

'

E o v e m e n t

# B0

C1

0 ; 1 D T D ; 9

2

E o v e m e n t

# B0

C1

0 ; 1 D T D ; 9

3

E o v e m e n t

Ashlyns school 18


19/27

(a) #he frame is mo,ed at a constant speed of '.0 cm s='

throgh the niformmagnetic field region as shown in the diagram.

(i) -or each position of the frame shown in the diagram either gi,e thedirection of the crrent throgh the ammeter or if there is no crrent state4no current5.

?osition 1= .......................................................................................................

?osition $= .......................................................................................................

?osition &= .......................................................................................................

(2)

(ii) #he total electrical resistance of the frame and ammeter is $.0 F.*alclatethe maximm crrent recorded "y the ammeter.

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9aximm crrent = ................................................. (4)

Ashlyns school 19


20/27

(") #he frame is now mo,ed with niform acceleration throgh the magnetic field.Explain how the magnitde of the crrent changes as the frame mo,es fromposition 1 throgh position $ to position &. o may "e awarded a mar for theclarity of yor answer.

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(4)(Total 10 marks)

9. 3


21/27

l a m p

E a g n e t

- l e c t r o n i c b a l a n c e

# l u m i n i u mr o d

#he switch is closed. #he reading on the "alance increases to 5'.4 g.

(a) (i) *alclate the additional force on the magnet when there is crrent in thecircit.

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-orce = ..........................................(1)

(ii) Explain how this additional force originates. o may "e awarded a mar

for the clarity of yor answer.

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... (4)

Ashlyns school 21


22/27

(") #he diagram "elow shows a plan ,iew of the rod and the poles of the magnet.

(i) ;n the diagram label the poles of the magnetto indicate the direction offield needed to prodce a downward force on the magnet.

%+EW 3S SEE7 -A;9 3:;%E

u r r e n ti n r o d

E a g n e t

) . $ c m

2 $ . $ c m

l a m p

# l u m i n i u m r o dI

(1)

Ashlyns school 22


23/27

(ii) #he rod is $0.0 cm long and the magnet is '.0 cm wide. #he magnetic flxdensity of the magnet is &0.0 m#. *alclate the crrent in the rod.

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*rrent = ..........................................(3)

(iii) #he direction of the crrent is re,ersed. What wold "e the new reading onthe "alance!

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:alance reading = ..........................................(2)

(Total 11 marks)

10. (a) State in or!sthe formla which gi,es the electric force "etween two chargedparticles.

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(2)

Ashlyns school 23


24/27

(") What are the "ase nits of the constant in this formla!

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(3)(Total 5 marks)

11. #his is an extract from an article on thnderstorms.

GThe electric field reuired to cause damp air to ionise, as happens in a lightning striHe, is

3 < '$'% m='. When this happens 40 * of charge passes "etween the clod (at aheight of 'Hm" and the ground. The striHe lasts 2$ ms, and completely discharges the cloud.I

The cloud and the ground below it may be modelled as a capacitor, as in the diagram.

= = = = = = = = = = = =

: : : : : : : : : : : :

) H m

l o u d

J r o u n d

*alclate the ,oltage "etween the clod and the grond when the strie occrs.

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%oltage = ...........................................(2)

Ashlyns school 24


25/27

Ashlyns school 25


26/27

*alclate the capacitance "etween the clod and the grond.

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*apacitance = ...........................................(2)

-ind an approximate ,ale for the resistance of the air "etween the clod and the

grond dring the strie.

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Aesistance = ...........................................

(2)

3 different way of modelling a thnder clod is to treat the charge of=*$ as a pointcharge at a height of ) Hm, as shown in the diagram below.

#ssume in this simple model that the ground has no effect on the field strength or shape.

) H m

J r o u n dX


27/27

(ii) calclate the ,ale of the electric field this point charge of=*$ would cause at thepoint X on the ground immediately below it,

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Electric field = ...........................................(2)

(iii) explain why one might expect the lightning strie to "egin from the clod and notfrom the grond.

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(1)(Total 11 marks)

electricity and magnetism q unit 4.rtf

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Transcript of electricity and magnetism q unit 4.rtf