A2 Unit 4 Topic 2 Electric and Magnetic Fields

8/12/2019 A2 Unit 4 Topic 2 Electric and Magnetic Fields

1/13

A2 Unit 4 Topic 2 Electric and Magnetic Fields

p41

Q1 What is the force on an electron in an

electric field of 300V.m-1?

19

17

17

300 1.602 10

4.806 10

4.8 10

F Eq

N

=

=

=

:

Q2 What is the strength of an electric field that

will !t a force of 1.28 " 10-1#$ on a roton?

1# 19

1#

19

3 1

1.28 10 1.602 10

1.28 10

1.602 10

7990

8.0 10 .

F Eq

E

E

V m

=

=

=

=:

Q3 %ow m!ch acceleration will an alha

article !ndergo whilst in an electric field of

10&V.m-1?

4 19

1#

1# 27

1#

27

11

11 2

10 2 1.602 10

3.204 10

3.204 10 4 1.67 10

3.204 10

4 1.67 10

4.7964 10

# 10 .

F Eq

N

F maa

a

m s

=

=

=

= =

=

=

:

Q4 'n the electron (eam of a cathode ra)

oscilloscoe* electrons are accelerated thro!gh a

otential difference of 3000V which is set !

(etween electrodes which are 3cm aart.

a+ ,alc!late the electric field strength (etween

these electrodes* ass!ming it is a !niform

field.

3

3

6 1

3000 3 10

3000

3 10

10 .

V Ed

E

E

V m

=

=

=

=

(+ %ow fast will the electrons (e moing when

the) emerge from this field?

31 2 19

19

31

7

7 1

19.109 10 3000 1.602 10

2

2 3000 1.602 10

9.109 10

3.2484 10

3 10 .

W Vq

v

v

m s

=

=

=

=

:c+ raw a ict!re to ill!strate the field rod!ced

() these lates.

d+ escri(e and e"lain how the field/s effects

wo!ld (e different if a roton were laced in

it.

The electron is accelerated to the right. A proton

would accelerate to the left, in the direction of the

electric field.

p43

Q1 "lain what wo!ld haen to an electron

which fo!nd itself at the e"act centre of the

electric field shown in fig 2.1.6(.

Assuming there are no other electric fields, the

electron would feel no force from either proton.

The net field is zero in the eact centre.

Q2 raw a air of electrons 8cm aart. n

)o!r diagram* add field lines to show the shae of

the electric field rod!ced () these electrons.raw in seeral e!iotential lines.

This diagram shows the actual equipotential lines

from this question. The !oundaries of the colours

give the equipotential lines.


2/13

The a!ove diagram shows the equipotential lines

and the field lines for two electrons.

Q3 air of flat* s!are metal lates is held

arallel to each other 10cm aart. ne is

connected to earth* and the other is connected to a

2000V "#$%s!l).

a+ What wo!ld the electrical otential (e at a

oint (etween the centres of the lates* which

are held 3cm from the earthed one?

4 1

4

2000

0.1

2 10 .

2 100.03

600

VE

d

V m

V

V V

=

=

=

==

(+ What difference in effect wo!ld there (e on

electrons within the field* one 1cm from the

earthed late* and the other in the e"act

midoint of the field?

A!solutel& nothing.

Q4 Wh) is the electric field in fig 2.1.6d

strongest near the oint of the steele?

$harge concentrates at points so the

steeple point would have the strongest electric

field around it.

Q5 'f fig 2.1.6a shows a h)drogen atom* then

the searation of the charges wo!ld (e #.3"10-11m.

'f the otential difference from the roton to the

electron5s osition is 27.2V* what is the strength

of the electric field along the line (etween the two

articles? ss!me the field is !niform* altho!gh

this is a simlification.+

11

11 1

27.2

#.3 10

#.1 10 .

VE

d

V m

=

=

=

p46

Q1 What is the force of attraction (etween a

!rani!m n!cle!s atomic n!m(er 92+ and an

electron at a distance of 0.1 nm?

( )

1 2

2

9 19 19

210

6

6

8.99 10 92 1.602 10 1.602 10

10

2.1226 10

2 10

'q qF

r

N

=

=

=

:

Q2

What is the strength of the electric field ca!sed ()

a gold n!cle!s atomic n!m(er 79+ at a distance of

1 " 10-12m from the centre of the n!cle!s?

( )

2

9 19

212

17

17

8.99 10 79 1.602 10

10

1.1378 10

1 10

'qE

r

N

=

=

=

:

What is the force of re!lsion (etween an alha

article and a gold n!cle!s when the alha article

asses () the n!cle!s at a distance of 1 m?

( )

1 2

2

9 19 19

212

2

2

8.99 10 79 1.602 10 2 1.602 10

10

3.64#4 10

4 10

'q qF

r

N

=

=

=

:

Q3 escri(e and e"lain a otential ro(lem

with the e"erimental set-! in fig 2.1.8 when

comaring res!lts with ,o!lom(/s law that

1 2

2

'( (F

r=

%int What wo!ld the metre r!ler (e meas!ring?+


3/13

The charge is spread across the surface of the

spheres and the electric field is not linear !ut

radial. The distance value would !e ver& difficult

to find as it would not directl& relate to the gap

!etween the spheres.

The change in weight would !e ver& small

compared to the weight of the stand on the scale

pan. This could !e an issue in terms of accurac&.

Q4 stimate the distance that )o! float a(oe

)o!r (ed at night as a res!lt of the ,o!lom(

re!lsion (etween the electrons in the (edsheets

and those in )o!r )amas.

Assume the !ed sheets and panamas are pure

car!on. Assume the sheet is )*+g and &our

p&amas are also )*+g in mass.

1

23 1

26 19

7

2#0

12 .

2.0833

2.0833 6.022 10 . 1

1.#0#6 10 1.602 10

2.4118 10

gNo moles

g mol

mol

No electrons mol atoms mol

electrons $

$

=

=

=

=

= Assume the forces follow $oulom!-s law

Assume !od& mass is /+'g

( )

( )

1 2

2

29 7

2

29 7

10

11

8.99 10 2.4118 1070 9.81

8.99 10 2.4118 10

70 9.81

8.726 10

10

'q qF

r

r

r

m

=

=

=

=

:

This, of course, is utter ru!!ish0

p48

Q1 :ig!re 2.1.13 shows a ositiel) charged

oil dro held at rest (etween two arallelcond!cting latesAand1.

a+ ;he oil dro has a mass 9.79 " 10-1#&g. ;he

otential difference (etween the lates is

#000V and late1is at a otential of 0V. 's

lateAositie or negatie?

A is negative so the electric field is verticall&

upwards.

(+ raw a la(elled free-(od) force diagram

which shows the forces acting on the oil dro.

c+ ,alc!late the electric field strength (etween

the lates.

2

2

# 1

#000 2.# 10

#000

2.# 10

2 10 .

V Ed

E

E

V m

=

= =

=

d+ ,alc!late the magnit!de of the charge < on

the oil dro.

1# #

1#

#

19

9.79 10 9.81 2 10

9.79 10 9.81

2 10

4.802 10

3 electron e!ialent charges

F Eq

q

q

$

=

=

= = =

e+ %ow man) electrons wo!ld hae to (e

remoed from a ne!tral oil dro for it to

ac!ire this charge?

2 electrons would have to !e removed for this.

p53

Q1 What is the caacitance of a caacitor

which stores 2 co!lom(s of charge for eer) 100

olts alied to it?


4/13

2

2

100

2 10

20

q$

V

F

mF

=

=

= =

Q2 0.01 : caacitor is charged () and thenisolated from an 8V ower s!l).

a+ ,alc!late the charge stored.

2

0.018

8 10

q$

V

q

q $

=

=

=

(+ ;he caacitor is then connected across another

identical caacitor which is !ncharged.

escri(e and e"lain what will haen to the

charge and oltage on each caacitor.

The E3F from the charged capacitor will force a

current to flow until the E3F is !alanced across

the two capacitors. 1ecause the capacitances are

equal, the charge will also !e equal and the E3F

half of the original 4 5V.

Q3 %ow m!ch energ) is stored on a #0:

caacitor which is charged to 12V?

12

12

10

#0 1012

#0 10 12

6 10

q$

V

q

q

$

=

=

=

=

Q4 1200 : caacitor is connected to a

oltage s!l) !ntil f!ll) charged with 10.8m,. 'f

this caacitor is then disconnected andreconnected across a 100W light (!l(* for how

long co!ld it light the (!l(?

This is a ridiculous question !ecause the light

!ul! is a non6ohmic element. The cold resistance

is far lower than the operating resistance. The

!ul! will drain the capacitor at a much faster rate

than the time indicated.

7lus, the capacitor will discharge in an

eponential fashion with the pea' current at the

start of the discharge and then taper off over time.The power output of the !ul! will drop

accordingl&.

( )

2

26

12

2

2

2

4

10.8 10

1200 10

9.72 10

9.72 10100

9.72 10

100

9.72 10

E Vq

q$

V

qV

$

qE

$

8

E7

t

t

t

s

=

=

=

=

=

=

=

=

=

=

p59

Q1 What is the time constant for a car

co!rtes) light in which a 2 m: caacitor

discharges thro!gh a 1# &= resistor?

3 3

1# 10 2 1030

9$

s

=

= =

Q2 %ow m!ch charge remains on a 0.04:

caacitor after 8 seconds* if it is discharging

thro!gh a #00= resistance and initiall) held 2, of

charge?

0

8

#00 0.04

1

2

0.4038

4 10

t

9$q q e

e

$

=

=

=

:

Q3


5/13

0

30

0.00669 0.03

0.00669 30ln

0.03

30

0.00669ln0.03

20.4127

> 20.41

t

9$

9$

: : e

e

9$

9$

s

=

=

=

=

=:

0.03 200

6

V :9

V

V

==

=

6200 100 10

0.02

9$

s

=

=

=

For the information given in the diagram, the

capacitance is too low !& a factor of ;+++. The

value of $ should !e ;++mF, not ;++>?A

(+ 'f this were a model of an a!tomatic hand

dr)er circ!it which re!ires 4.0V to oerate*

!se the grah to wor& o!t for how long it will

remain on.

4 200

0.02

V :9

:: A

=

=

=

t @ +.+)A Bs

c+ %ow wo!ld )o! alter the circ!it so that the

dr)er remains on for 30s?

4

4

0

30

10

30

10

4

4

#

4 6

4

6

4 30

ln 6 10

30

4ln 10

6

7.399 10

700

t

9$

9

9

V V e

e

e

9

9

'

=

=

=

=

=

= :

0

30

200

30

200

1

4 6

4

6

4 30ln

6 200

30

4ln 200

6

3.699 10

400

t

9$

$

$

V V e

e

e

$

$

mF

=

=

=

=

=

= :

Either increase the resistance to /++'C or the

capacitance to 5++mF. This will allow the voltageto !e at 5V after 2+s.

Again, this is a ridiculous question as a hand

dr&er uses )++W plus to operate, far more than is

availa!le in this scenario.

Q4 raw an acc!rate s&etch grah for the

c!rrent thro!gh a discharging #0@: caacitor

which is f!ll) charged () a 6V s!l) and then

discharged thro!gh a 10&= resistance* oer a

eriod of 2 seconds.

Q5 defi(rillator is a machine that is !sed to

correct irreg!lar heart(eats () assing a large

c!rrent thro!gh the heart for a short time. ;he

machine !ses a 6000V s!l) to charge a

caacitor of caacitance 20:. ;he caacitor is

then discharged thro!gh metal electrodes

defi(rillator addles+ laced on the chest of the

atient.

a+ ,alc!late the charge on the caacitor lates

when charged to 6000V.


6/13

12

7

20 106000

1.2 10

q$

V

q

q $

=

=

=

(+ ,alc!late the energ) stored in the caacitor.

7

4

6000 1.2 10

7.2 10

E Vq

8

==

=

c+ When the caacitor is discharged* there is an

initial c!rrent of 40 thro!gh the atient.

,alc!late the electrical resistance of the (od)

tiss!e (etween the metal electrodes of the

addles.

6000 40

1#0

V :9

9

9

=

= =

d+ ss!ming a constant discharge rate of 40*

calc!late how long it wo!ld ta&e to discharge

the caacitor.

7

7

9

1.2 1040

1.2 10

40

3 10

3

q:

t

t

t

s

ns

=

=

=

= =

e+ 'n ractice the time for discharge is longer

than this calc!lated time. A!ggest a reason for

this.

$apacitors discharge through ohmic resistors

with an eponentiall& decreasing current. Also,there is no reason to thin' that a human !od& is

ohmic in its !ehaviour, i.e. V = :9.

p63

Q1 escri(e the !se of :leming/s left hand

r!le.

The thum!, first and second fingers are held at

mutuall& perpendicular directions. The thum!

represents the force eperienced !& a chargemoving in a magnetic field at a direction

perpendicular to the plane of motion and

magnetic field. The first or inde finger represents

the direction of the magnetic field. The middle

finger represents the direction of motion of a

positivel& charged particle or the conventional

current in a wire.

Q2 ,o) the diagrams in fig. 2.3.8 and draw

an arrow to show the direction of an) force acting

on the wire in each case.

Q3 Ban) real motors !se electromagnets to

create the magnetic field that ca!ses their rotor to

sin. Cie one adantage and one disadantage of

(!ilding a motor which !ses electromagnets rather

than ermanent magnets.

Advantages The strength of the magnetic field

can !e controlled to increase or decrease the

torque of the motor.

The motor can !e started in small stages rather

than with full power. A full power start uses ver&

high currents and creates ver& high torques at low

speeds.

Disadvantage The stator coils generate heat and

consume energ&.

7ermanent magnets tend to !e smaller in size than

compara!le electromagnets, so the motor size in

increased.

P67


7/13

# 19 2

21

21

# 10 1.602 10 # 10

4.00# 10

4 10

F 1qv

N

=

=

=

:

c+ %ow fast wo!ld a roton need to trael in

order for the electromagnetic force on it to (e

s!fficient to ma&e it or(it the arth at thes!rface? Dadi!s of arth E 6.4 " 106m.+

,omment on )o!r answer.

27

6

19 #

19 # 6

27

10

10 1

1.672 106.4 10

1.602 10 # 10

1.602 10 # 10 6.4 10

1.672 10

3.066 10

3 10 .

mvr

q1

v

v

m s

=

=

=

= :

This is 100 times the speed of light, which is

impossible.

Q2 Aeed E distanceFtime and c!rrent E

chargeFtime. "lain how : E G'l is act!all) the

same e!ation as : E G (!t considered for

man) charges in a gro!.

F 1:l

q:

t

qF 1 l

t

l1q

t

1qv

=

=

=

=

=

Q3 :or the inestigation on ta(le salt in the

wor&ed e"amle a(oe* calc!late the difference in

the radii of c!rat!re that wo!ld (e fo!nd if the

coman) inestigated the two isotoes of sodi!m23$aH and 22$aH. "lain wh) s!ch small

differences can (e easil) detected () a machine

li&e that shown in fig. 2.3.12.

2

22

12

23

12

22

27 12

19

6

23

27 12

19

1

2

2 2.

7.3737 10

7.2116 10

22 1.672 10 7.3737 10

1.602 10

1.69 10

23 1.672 10 7.2116 10

1.602 10

1

DE Vq mv

Vqv Vq

m m

For Na

v Vq

For Na

v Vq

mvr

q1

For Na

Vqr

1

r1

Vq

For Na

Vqr

1

r1

Vq

= =

= =

=

=

=

=

=

=

= 6

6

6

.73 10

1.73 101.024

1.69 109atio

= =

Therefore, there is a ).5 difference in theradius, assuming the ionisation, accelerating

voltage and magnetic field are the same for !oth.

This is easil& detected.

p71


8/13

Q1 What is the fl!" lin&age if a s!are coil

with 10 cm sides and haing #00 t!rns interacts

with a magnetic field* G E 0.33 m;?

( )2

4 1

3 2

3.3 10 10 #00

1.6# 10 .

1AN

T m

=

=

=

Q2 ;he grah shown in fig. 2.3.19 is a trace of

ind!ced emf against time as a magnet is droed

thro!gh a coil of wire.

a+ escri(e and e"lain the trace o(tained.

The positive voltage shows an increase of

magnetic flu as the magnet enters. The pea'

voltage is when the rate of change of flu is

greatest. The drop in voltage shows that the rate

of flu increase drops off as the magnetic field

aligns with the motion of the magnet in the plane

of the coil.

The negative voltage shows a decrease of

magnetic flu through the coil as the other pole of

the magnet passes through the coil.

ee diagrams !elow.

(+ 'f the coil were connected in series to a light

(!l(* descri(e and e"lain how the c!rrent

thro!gh the (!l( wo!ld ar) oer time.

The current in the !ul! would reflect the emf

created in the coil in terms of direction and

magnitude.

Q3 ;he coil from !estion 1 is t!rned thro!gh

90I within the 0.33m; magnetic field* moing

from a osition erendic!lar to the field* to a

osition arallel to the field. ;his action ta&es

12ms. What is the ind!ced emf in the coil? %ow

wo!ld JenK/s law ca!se the ind!ced c!rrent to

affect the moement?

3

3

1

1

1.6# 10

12 10

1.37# 10

1.4 10

t

1AN

t

V

=

=

=

=

:

Q4 transformer for a to) train set conerts

the mains s!l) from 230V down to 6V tooerate the model train. ;he transformer that

ma&es this conersion has 160 t!rns on its

secondar) coil. %ow man) rimar) t!rns does the

transformer hae?

6 160

230

2301606

6133

o s

i p

p

p

V n

V n

n

n

turns

=

=

=

=

p73

Q1 What was the diameter of Gr!sh/s wind

t!r(ine in metres?

*>ft in diameter.

Q2 'f the (r!sh s)stem were oerating at thehighest allowed oltage 90V+ and rod!cing

12&W* what c!rrent wo!ld (e deliered to each of

the 12 arallel (atteries of cells?

312 10 90

133.3

F 133.3 F12

11.1

11

7 V:

:

:

: cell

A

=

=

=

=

=

&

&

&

:

Q3 'f a st!dent were to (!ild a model wind

t!r(ine to light an J* list the main arts of the

model that wo!ld (e needed and what their


9/13

f!nction is L a diagram ma) hel )o!r

e"lanation.

A wind tur!ine requires a device to garner energ&

from the wind. A !lade or tur!ine "as shown

a!ove% would do. This connects to a generator

which converts 'inetic energ& to electrical energ&.

The GE# then converts electrical energ& to heat

and visi!le light.

Q4 "lain the enironmental imortance of

deeloing increased !se of wind ower

electricit) generation s)stems. 'n )o!r answer*

disc!ss the ro(lems which will slow the ace of!ta&e of wind ower as an alternatie to non-

renewa(le energ) so!rces.

1est evidence and models indicate that the Earth

is warming as a result of 3an-s use of fossil fuels

that has increased the $H)concentration in the

atmosphere.

Ising renewa!le sources of energ&, such as wind

power, reduces the use of fossil fuels to generate

power and hence reduces the amount of $H)

!eing poured into the atmosphere.#isincentives include the relativel& high cost of

the infrastructure and the power produced, as

well as the intermittent nature of the wind,

resulting in unrelia!le power generation.

Q5 ,arr) o!t some research on the ro(lem of

aria(le wind ower s!l). Write a aragrah to

e"lain how this ro(lem is (eing oercome.

p74Q1 ne ractical arrangement for erif)ing

,o!lom(/s law is to !se a lightweight* negatiel)-

charged* freel)- s!sended (all. 't is reelled ()

the negatie charge on a larger shere that is held

near it* on an ins!lated s!ort. ;he small angle of

deflection Jis then meas!red.

;he weight of the

(all is W. Ahow that the force of re!lsion : on

the s!sended (all is gien ()

F = W.Tan"J%2+

st!dent ta&es seeral sets of readings () moing

the larger shere towards the s!sended (all in

order to increase the m!t!al force of re!lsion

(etween them. %e meas!res the angle of

deflection Jand the searation distance rin each

case. %e then calc!lates the magnit!de of the

force :.

%ere are some of his res!lts.

:orce :F10-3$ 142 #68

istance rF10-3m 36.0 27.0 18.0 9.0

,alc!late the al!es that )o! wo!ld e"ect the

st!dent to hae o(tained for the missing forces*

ass!ming that ,o!lom(/s law was o(e)ed.

Write )o!r answers in a co) of the ta(le. 4+

( )

( )

1 2

2

3

3

9

1 2

23

23 3

1 2 9

1# 2

142 10

8.99 10

18 10

142 10 18 10

8.99 10

#.1177 10

'q qF

rF N

q q

q q

$

=

=

=

=

=


10/13


11/13

3

# 1

# 19

14

14

3000

2# 10

1.2 10 .

1.2 10 1.602 10

1.922 10

2 10

VE

d

V m

F Eq

N

=

=

= =

= =

:

,o) and comlete the grah to show how the

force on the electron aries as the distance of the

electron aries from the (ottom late to the to

late.

2+

;his force ca!ses the electron to accelerate.

;he electron is initiall) at rest in contact with the

(ottom late when the otential difference is

alied. ,alc!late its seed as it reaches the !er

late. 3+

19

19

212

19

31

7

7 1

3000 1.602 10

4.806 10

2 4.806 10

9.109 10

3.248 10

3.2 10 .

W Vq

8

mv

v

m s

==

=

=

=

=

:

;otal 11 mar&s+

Q4 efine caacitance. 2+

$apacitance is the charge stored in a capacitor

divided !& the voltage across the terminal of a

capacitor.q

$V

=

n !ncharged caacitor of 200@: is connected in

series with a 470&= resistor* a 1.#0V cell and a

switch. raw a circ!it diagram of this

arrangement. 1+

,alc!late the ma"im!m c!rrent that flows. 2+

0

0

3

6

1.#

470 10

3.191# 10

3.2

t

9$: : e

V:

9

A

=

=

=

= :

A&etch a grah of oltage against charge for )o!r

caacitor as it charges. 'ndicate on the grah the

energ) stored when the caacitor is f!ll) charged.

4+

12

212

6 212

4

4

200 10 1.#

2.2# 10

2 10

E Vq

$V

8

=

=

=

=

:


12/13

,alc!late the energ) stored in the f!ll)-charged

caacitor. 2+ ;otal 11 mar&s+

Q5 ;he diagram shows a grah of charge

against oltage for a caacitor.

What !antit) is reresented () the sloe of the

grah? 2+

lope is the capacitance.What !antit) is reresented () the shaded area?

2+

haded area is the energ& in the capacitor.

n electronic camera flash g!n contains a

caacitor of 100@: which is charged to a oltage

of 2#0V. Ahow that the energ) stored is 3.1M. 2+

12

212

6 212 100 10 2#0

3.12#

3.1

E Vq

$V

8

=

=

= =:

;he caacitor is charged () an electronic circ!it

that is owered () a 1.#V cell. ;he c!rrent drawn

from the cell is 0.20. ,alc!late the ower from

the cell and from this the minim!m time for the

cell to recharge the caacitor. 3+ ;otal 9 mar&s+

1.# 0.2

0.3

3.12#0.3

10.416

10

7 V:

W

E7

t

t

t

s

=

= =

=

=

=:

Q6 ;he magnit!de of the force on a c!rrent-

carr)ing cond!ctor in a magnetic field is directl)roortional to the magnit!de of the c!rrent in the

cond!ctor. With the aid of a diagram descri(e how

)o! co!ld demonstrate this in a school la(orator).

4+

The power suppl& provides the current in the

&ellow wire. This wire is held in place !& clamps

"not shown%. The la!orator& scales measure the

weight of the I6shaped magnet. When the current

flows, the weight of the magnet will change

amount of force eerted !& the current on the

magnetic field. F = !l

The second diagram showelectric current going into the

page. The direction of the

magnetic field and the

current gives a net

downwards force on the

conductor. This gives a net

upwards force on the magnets. "Newton-s 2rdlaw%

t a certain oint on the arth/s s!rface the

horiKontal comonent of the arth/s magnetic field

is 1.8 " 10

-#

;. straight iece of cond!cting wire2.0 m long* of mass 1.#g lies on a horiKontal

wooden (ench in an east-west direction. When a

er) large c!rrent flows momentaril) in the wire it

is !st s!fficient to ca!se the wire to lift ! off the

s!rface of the (ench.

Atate the direction of the c!rrent in the wire. 1+

The current must flow towards the West.

"Fleming-s left hand rule%

,alc!late the c!rrent. 2+

3 #

3

#

1.# 10 9.81 1.8 10 2

1.# 10 9.81

1.8 10 2

411.48

410

F 1:l mg

:

:

A

= =

=

=

=:

What other noticea(le effect will this c!rrent

rod!ce? 1+ ;otal 8 mar&s+

A current of this size would cause su!stantialheating of the wire.

Assume the wire is made from copper.


13/13

3

2

3

4

1.# 108890

2

1.# 10

2 8890

#.1792 10

mass

Vol

r

r

m

=

=

=

=

( )

8

24

2

2

2 2

3

1.72 10 2

#.1792 10

4.0821 10

411.48 4.0821 10

6.9117 10

6.9

G9

A

7 V: : 9

'W

=

=

=

= =

=

= :

This situation produces approimatel& /'W of

power dissipated !& the wire. $opper has a

specific heat capacit& of 2B/8.'g6;.$K6;and a

melting temperature of ;2*>K$. Assuming a

starting temperature of )+K$

( )3387 1.# 10 13#6 20

776

776

6912

0.11

( $m t

8

W7

t

t

s

= =

=

=

=

=

:t would ta'e a!out a tenth of a second to melt the

copper wire.

Q7 ;he diagram shows a rectang!lar coil

A2 Unit 4 Topic 2 Electric and Magnetic Fields

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Transcript of A2 Unit 4 Topic 2 Electric and Magnetic Fields