28. Electromagnetic Induction (2)

8/16/2019 28. Electromagnetic Induction (2)

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Chapter 28: Electromagnetic Induction

Please remember to photocopy 4 pages onto one sheet by going A3→A4 and using back to back on the photocopier.

Electromagnetic Induction occurs when an emf is induced in a coil due to a changing magnetic flux.

We have seen from the last two chapters that Electricity and Magnetism are inter-linked.

The English scientist Michael Faraday investigated this relationship.He found that if you moved a magnet in or out of a coil of wire a voltage was generated !more properly called an emf!electromotive force".He also realised that the #uicker you moved the magnet !or the coil" the greater was the emf generated.This is now known as Faraday$s %aw of Electromagnetic &nduction.

Demonstrating Faraday’s Law

'. Move the magnet in and out of the coil slowly and note a slight deflection.(. Move the magnet #uickly and note a greater deflection.

%ater on it was found that the direction of the emf could also )e predicted.

This is known as %en*$s %aw.The two laws together are known as the laws of Electromagnetic &nduction

The Laws o Electromagnetic Induction!

'. Faraday’s Law states that the size of the induced emf is proportional to the rate of change of flux.(. Len"’s Law states that the direction of the induced emf is always such as to oppose the change producing it.+

Magnetic Flu#

To calculate the si*e of the induced emf we need one more concept, Magnetic Flux.The sym)ol for magnetic flux is !pronounced sigh/".The unit o magnetic lu# is the $e%er &$%'(

To introduce the idea of magnetic flux consider an area A in a uniform magnetic field.When the magnetic force lines are perpendicular to this area !see diagram" the total flux !" through the area isdefined as the product of B )y A.

The magnetic flux can )e visualised as the num)er of magnetic field lines passing through a given area.The num)er of magnetic field lines per unit area i.e. B is then referred to as the density of the magnetic flux or more

properly the magnetic flux density.

0ow we are in a position to calculate the induced emf1

2emem)er Faraday$s %aw1 The si*e of the induced emf is proportional to the rate of change of flux.

&n this case the proportional constant turns out to )e ' !remem)er where we came across this )efore3 Hint1 F 4 ma"

5o

&n 5ym)ols1

!the minus sign is a reference to %en*$s %aw".

Finally this formula assumes the coil has only one turn. &f there are 0 turns then the formula )ecomes

'

6hanging flux ⇒ induced emf ⇒ induced current ⇒ magnetic field

4 BA

E 4 &nduced emf 4 - !Final Flux 7&nitial Flux" 8 time taken

E 4 -0!Final Flux 7&nitial Flux" 8 Time Taken



9lastic pipe

Magnet

6opper pipe

Magnet

Thread :

llsddf

Magnet

Len"’s Law

Len"’s Law states that the direction of the induced emf is always such as to oppose the change producing it.

E#planation

We know that when a magnet and coil move relative to each other an emf is induced. 0ow if the coil is a conductor the induced emf will drive a current around the coil.This current has a magnetic field associated with it.The direction of this magnetic field will always )e such as to oppose the change which caused it.

Demonstrating Len"’s Law &i': Magnet) *lastic and Copper Tu%es(

+pparatus

6opper pipe plastic pipe stopwatch strong neodymium magnet piece of neodymium or iron !same si*e as magnet".*rocedure

;rop the neodymium magnet down )oth tu)es and compare the time taken for eachfor each.,%ser-ation

The time taken for the magnet to fall down through the copper tu)e is much longer than the time taken for the magnet to fall down the plastic tu)e.E#planation

The moving magnet induces an electric current in the copper. This current creates amagnetic field that exerts a force to oppose the motion of the magnet and hence slows it down.

Demonstrating Len"’s Law &ii': Magnet and +luminium .ing

+pparatus

<luminium ring magnet thread retort stand.*rocedure

'. Move one end of the )ar magnet towards and into the ring. The ring movesaway from the magnet.

(. Hold the magnet in the ring and #uickly pull it away. The ring follows themagnet.

,%ser-ation

When the magnet moves the ring responds )y moving in the same direction.E#planation

The moving magnet induces a current in the ring. This current creates a magneticfield that exerts a force to oppose the motion of the magnet. The magnet exerts ane#ual and opposite force on the ring and so the ring moves as o)served.

(



Electric /enerators

%et$s take a look at that very first diagram again1Here mechanical energy is )eing converted to electrical energy.This is the action which is responsi)le for almost all our electricity generation!solar energy )eing the main exception".&f you follow the electric wires in your house )ack to their source you will find atthe other end a generating station which has either a magnet moving in and out of

a coil of wire or more likely a coil of wire rotating in a magnetic field.

+n Electric /enerator is a de-ice that con-erts mechanical energy to electrical energy!

0ote that in the diagrams on the right the voltage is changing directionin a sine-wave fashion.The generators in power plants are designed to change direction =>times a second !fre#uency 4 => Hert*".?ecause the voltage drives the current it follows that the current alsochanges direction => times a second.

+lternating Current &+!C!'(

<lternating current is current which continually changes direction.Mains electricity consists of current which changes direction )etween@> and => times a second.

Comparing +lternating and Direct 0oltage and Current

We have a pro)lem.

&f the current !or voltage" is constantly changing how can we say what its value is3We can$t take the average value )ecause it$s *ero.We could take the height of the wave 7 )ut this keeps changing with time.We could take the maximum height 7 )ut if the maximum height is say A <mps it still won$t have the same heatingeffect as a direct current of A <mps.

To solve the pro)lem we use a little mathematical trickery1We use what$s known as the root mean s#uare value !Br.m.s."This is o)tained )y dividing the maximum value !Bmax " )y √(.

We do this )ecause the magnitude of the r.m.s. alternating current will have the same heating effect as a direct current of the same magnitude.e.g. &f the r.m.s. value of an alternating current is ( <mps it will the same heating effect as ( <mps direct current.

A

0rms 1

V max

√ 2 Irms 1

I max

√ 2



B

Bin BB Boout

Mutual Induction

When the emf field in one coil changes an emf is induced in the other.

To Demonstrate Mutual Induction

*rocedure• 5et up two coils side )y side as shown.• 6lose the switch 7 a deflection is seen on the galvanometer.• Cpen the switch 7 a larger deflection is o)served.,%ser-ation

Each time the circuit is completed or )roken a deflection is o)tainedon the galvanometer. The deflection at the )reak is greater than at themake.E#planation

<t the make and )reak of the circuit there is a change in the magnetic flux linking the coils and so an emf is induced inthe secondary coil.The deflection is greater at the )reak )ecause the current drops more #uickly than it increases.

Mutual Induction and the Transormer

+pparatus

D B a.c. power supply coils of wire 7 @>> turns and >> turns soft iron core two a.c. voltmeters.

*rocedure'. 5et up the apparatus as shown.(. 5witch on the a.c. supply !left hand side"..

,%ser-ation< continuous reading is o)tained on thevoltmeter.Conclusion

The a.c. produces a constantly changing magnetic field.

The si"e o the induced em may %e increased %y

'. Having the coils nearer each other (. Winding the coils on the same soft iron core

This is the principle behind how a transformer works

The relationship %etween 0oltage out and 0oltage in or a Transormer

The relationship )etween voltage across the secondary coil !Bs" and voltage across the primary coil !Bp" isdetermined )y the ratio of the num)er of turns on the secondary coil !0s" to the num)er of turns on the primary coil!0p"

Bs 4 voltage across the secondary coil Bp 4 voltage across the primary coil 0s 4 0um)er of turns in secondary 0p 4 0um)er of turns in primary coil

ote

&f the voltage is increased the transformer is called a 5tep-Gp Transformer$&f the voltage is decreased the transformer is called a 5tep-;own Transformer$

@

6hanging emf !in first coil" ⇒ changing current !in first coil" ⇒ changing magnetic flux !in first coil"⇒ induced emf !in second coil". This in turn can induce a current if the second circuit is complete.

6onstantly changing emf !in first coil" ⇒ constantly changing current !in first coil" ⇒ constantly changingmagnetic field !in first coil" ⇒ constantly changing induced emf !in second coil" ⇒ constantly changingcurrent !in second coil if it$s a complete circuit".

Np

Ns

Vp

Vs=



D B

&ron core

3ses o transormers

Transformers are used in generating stations to step up the voltage from a)out (> kB to anything up to @>> kB !canyou remem)er why3 Hint1 oules$ %aw"This has then to )e dropped down to (A> Bolts )efore it enters the home.Many household appliances run on lower voltages again and so a second transformer is re#uired. This is usuallyinside the appliance !e.g. a radio".

4uestion to ma5e you thin5 &otherwise 5nown as $TF6'

<ccording to this if the voltage out is '>> times greater than the voltage in then the current out is '>> times less thanthe current in.?ut from Chm$s %aw !B 4 &2" if the voltage increases then so also does the current.What gives33

7elInduction

< changing emf in a coil induces a changing magnetic field in the coil itself. This changing magnetic field in turninduces a second emf !in the coil itself" which is opposite in direction to the driving emf.

This induced emf is known as )ack-emf !)ecause it is acting )ackwards$"

To Demonstrate 7elInduction &9ac5 Em'

+pparatus

D B a.c. power supply coil of wire with '(>> turns soft iron core D B filament lamp.

*rocedure

'. 6onnect the )ul) coil and a.c. supply in series.(. 5witch on the power supply. The lamp lights.A. &nsert the iron core into the coil. The lamp )ecomes dimmer.E#planation

The a.c. produces a changing magnetic field in the coil.This induces an emf and hence a current that opposes the applied current.The iron core increases the magnetic flux and hence the induced opposing current is increased.The resultant current in the circuit is reduced and the )ul) )ecomes dimmer.

ote

&f this circuit is set up using a d.c. power supply no dimming occurs with the core in the coil as there is no changingmagnetic field.

&t should now )e apparent that a coil of wire can )e used to reduce alternating current in the same way that a normalresistor is used to reduce ;irect 6urrent.The coil when used in this fashion is known as an inductor.

+n inductor is an electrical component used to reduce the flow of alternating current.<n example of an inductor is the dimmer switch used in stage lighting.

=

6hanging emf ⇒ changing current ⇒ changing magnetic field ⇒ induced changing emf !in oppositedirection to original" ⇒ induced changing current !in opposite direction to original" Iall in the same coilJ



Lea-ing Cert *hysics sylla%us

Content Depth o Treatment +cti-ities 7T7

! Electromagnetic

induction

Magnetic flux K 4 BA

Faraday$s law.;emonstration of the

principleand laws ofelectromagnetic induction.

+ppropriate calculations!

<pplication in generators.

%en*$s law.6hange of mechanical energy to electrical energy.

;! +lternating

current

Bariation of voltage and currentwith time i.e. alternating voltagesand currents.*ea5 and rms -alues o alternating currents and

-oltages!

Gse oscilloscope to showa.c.

Compare pea5 and rms

-alues!

0ational grid and a.c.

<! Concepts o

mutual

induction and

selinduction

Mutual induction &two ad=acent

coils': when the magnetic ield

in

one coil changes an em is

induced in the other) e!g!

transormers!

7elinduction: a changing

magnetic

ield in a coil induces an em in the coil itsel) e!g! inductor!

Demonstration.

Demonstration.

5tructure and principle of operation of a transformer.

;emonstration.<ppropriate calculations!voltage".

Gses of transformers.

Effects of inductors on a.c. !no mathematics or phase relations".

;immer switches in stage lighting 7 uses of inductors.

D



E#tra Credit

Len"’s Law states that the direction of the induced emf is always such as to oppose the change producing it.+<n alternative !less formal" definition is to say that the direction of the induced magnetic field will always )e such asto oppose the change producing it. We don$t specify magnetic field )ecause there will only )e an inducted magneticfield if there is an induced current which will only happen if there is a complete circuit whereas there will always )ean induced emf.This is a conse#uence of the conservation of energy 7 if the induced magnetic field attracted the magnet then themagnet would move faster resulting in a greater induced emf and magnetic field resulting in magnet moving faster

still and eventually would )reak the speed of lightLThe unit o magnetic lu# is the $e%er &$%'(

0amed after 9rofessor We)er 7 he was a professor who lectured <l)ert Einstein. Einstein held him in contempt )ecause We)er refused to give any time to recent developments in 9hysics developments which contradicted 7 or atthe very least #uestioned 7 the traditional teachings.Einstein refused to address We)er )y his proper title Herr 9rofessor We)er instead he addressed him as Herr We)er.We)er in turn refused to write a reference for Einstein !mind you the fact that Einstein couldn$t )e )othered going toWe)er$s lectures pro)a)ly didn$t help".End result3Einstein could only get a :o) as a lowly clerk in a patent office. This did have the advantage of providing Einstein witha lot of free time to think time which he appears to have put to good use.

(Demonstrating Len"’s Law &i': Magnet) *lastic and Copper Tu%es

< practical use of this in the real world is in the design of elevators.They have strong magnets attached to their outer walls and the lift shafts have copper linings so even if the elevator

)ecomes detached from its ca)le it cannot fall faster than the eddy currents and %en*s %aw will allow.There is a model of this in the Science in Action video1 NElectricity and MagnetismN where Howie investigates theTrocadero 6entre in %ondon.The 5heer Drop amusement rides use permanent magnets to )ring the ride to rest at the end of the fall.

(+lternating Current

Trust you will avoid the gigantic mistake of alternating current/.%ord Oelvin !'(@-'P>Q"

Tesla !remem)er him" was generating electricity in the form of alternating current )ut his great rival at the time wasEdison who favoured direct current. Edison roped in Oelvin to )ack him !Oelvin was recognised as the greatest livingscientist at the time" )ut even with the )acking of Oelvin he still lost out to Tesla !this one time".

< good analogy to help you understand the flow of the electrons caused )y potential difference is to imagine pushing astiff )icycle chain around and around.Each link is an electron and they all move at the same speed.<lternating 6urrent is therefore analogous to pushing and pulling the chain switching directions => times a second!alternating current alternates at a fre#uency of => hert*".

Why aren$t %aptops allowed to )e used on airplanes3The rate of change of flux generated )y the new generation of computer chips can )e very significant- not )ecause thestrength of the magnetic field is significant )ut )ecause the fre#uency is so high !( RH* plus".

The airline world isnt a)solutely sure what does or doesnt constitute a threat to safety.<nd the evidence of pro)lems is largely anecdotal.Their )est policy is to )an <%% electronic devices other than their own )uilt in systems which have of course )eensu):ect to flight testing.

< source of High Boltage )ut %ow current is the Ban de Rraff generator < source of High 6urrent )ut %ow Boltage is the Transformer used to melt nails.

+cti-ities

Take a )attery with a wire on each terminal, <ttach one end to a metal file.5crape the end of the other wire along the file )eside an <M radio and listen to the crackles... furthermore, radio theold-fashioned way )egan with sparks.

Make radio waves )y switching off an electric circuit and detecting them as NcrackleN on a long-wave radio.

Q



E#am 4uestions

'. S(>>AExplain the term emf

(. S(>>S(>>@S(>>(S(>>( C%S(>>@ C%S(>>Q C%S(>> C%What is electromagnetic induction3

A. S(>> C%< magnet and a coil can )e used to produce electricity.How would you demonstrate this3

@. S(>>= C%!i" < coil of wire is connected to a sensitive galvanometer as shown in the diagram.

What is o)served when the magnet is moved towards the coil3!ii" Explain why this occurs.!iii" ;escri)e what happens when the speed of the magnet is increased.

=. S(>'> C%!i" ;raw a sketch of the apparatus Michael Faraday used to generate electricity.!ii" What name is given to the generation of electricity discovered )y Michael Faraday3!iii" What energy conversions takes place in Faraday$s experiment!iv"How does Faraday$s experiment show that a changing magnetic field is re#uired to generate electricity3

D. S(>>QS(>>=S(>'>5tate Faraday$s law of electromagnetic induction.

Q. S(>>(5tate %en*$s law of electromagnetic induction.

. S(>>S(>>A5tate the laws of electromagnetic induction.

P. S(>>@S(>>( C%;escri)e an experiment to demonstrate electromagnetic induction.

'>. S(>>Q;escri)e an experiment to demonstrate Faraday$s law.

''. S(>>@!i" < light aluminium ring is suspended from a long thread as shown in the

diagram.When a strong magnet is moved away from it the ring follows the magnet.Explain why.

!ii" What would happen if the magnet were moved towards the ring3

'(. S(>>!i" < )ar magnet is attached to a string and allowed to swing as shown in the diagram.

< copper sheet is then placed underneath the magnet. Explain why the amplitude of the swingsdecreases rapidly.!ii" What is the main energy conversion that takes place as the magnet slows down3

'A. S(>>A!i" < small magnet is attached to a spring as shown in the diagram.

The magnet is set oscillating up and down. ;escri)e the current flowing in the circuit.!ii" &f the switch at < is open the magnet will take longer to come to rest. Explain why.



'@. S(>>DS(>>=;efine magnetic flux.

'=. S(>>D< coil has =>>> turns.What is the emf induced in the coil when the magnetic flux cutting the coil changes )y U '> 7@ W) in >.' s3

'D. S(>>P

What is the average emf induced in a coil of (> turns when the magnetic flux cutting it decreases from (.A W) to'.@ W) in >.@ s3

'Q. S(>>!i" < metal loop of wire in the shape of a s#uare of side = cm enters a magnetic field

of flux density T.The loop is perpendicular to the field and is travelling at a speed of = m s 7'.How long does it take the loop to completely enter the field3

!ii" What is the magnetic flux cutting the loop when it is completely in the magneticfield3

!iii" What is the average emf induced in the loop as it enters the magnetic field3Ithe diagram wasn$t in the original #uestion )ut it may )e useful here to help picture the situationJ

'. S(>>=!i" < s#uare coil of side = cm lies perpendicular to a magnetic field of flux density @.> T.

The coil consists of (>> turns of wire. What is the magnetic flux cutting the coil3!ii" The coil is rotated through an angle of P>o in >.( seconds. 6alculate the magnitude of

the average e.m.f. induced in the coil while it is )eing rotated.Ithe diagram wasn$t in the original #uestion )ut it may )e useful here to help picturethe situationJ

'P. S(>>D2ead the following passage and answer the accompanying #uestions.

The growth of rock music in the 'PD>s was accompanied )y a switch from acoustic guitars to electric guitars. Theoperation of each of these guitars is radically different.The fre#uency of oscillation of the strings in )oth guitars can )e ad:usted )y changing their tension. &n theacoustic guitar the sound depends on the resonance produced in the hollow )ody of the instrument )y thevi)rations of the string. The electric guitar is a solid instrument and resonance does not occur.5mall )ar magnets are placed under the steel strings of an electric guitar as shown. Each magnet is placed inside acoil and it magnetises the steel guitar string immediately a)ove it. When the string vi)rates the magnetic fluxcutting the coil changes an emf is induced causing a varying current to flow in the coil. The signal is amplifiedand sent to a set of speakers.imi Hendrix refined the electric guitar as an electronic instrument. He showed that further control over the musiccould )e achieved )y having coils of different turns.!<dapted from Europhysics 0ews !(>>'" Bol. A( 0o. @"

!a" Why must the strings in the electric guitar )e made of steel3!)" Why does the current produced in a coil of the electric guitar vary3!c" What is the effect on the sound produced when the num)er of turns in a coil is increased3

(>. S(>>DS(>'> The peak voltage of the mains electricity is A(= B. 6alculate the rms voltage of the mains.

('. S(>>@ 5ketch a voltage-time graph of the (A> B supply.

((. S(>> C% Electricity produced in a generating station is a.c. What is meant )y a.c.3

(A. S(>>D

5ketch a graph to show the relationship )etween current and time for !i" alternating current!ii" direct current.

P



(@. S(>>A C% What is a diode3

(=. S(>>A C% Rive an example of a device that contains a rectifier.

(D. S(>>@ C%S(>>= C% 0ame a device that is )ased on electromagnetic induction.

Transormers

(Q. S(>>A C%

What is a transformer used for3(. S(>>( C%S(>>Q C%

The transformer is a device )ased on the principle of electromagneticinduction.

0ame two devices that use transformers.

(P. S(>>Q C%S(>>@ C% S(>>( C% 0ame the parts of the transformer la)elled < ? and 6 in the diagram.

A>. S(>>( C%How is the iron core in a transformer designed to make the transformer more efficient3

A'. S(>>( C%The efficiency of a transformer is P>V. What does this mean3

A(. S(>>A C%5tate one energy conversion that takes place in an electrical generator.

AA. S(>>( C%The mains electricity supply !(A> B" is connected to the input coil of a transformer which has @>> turns. Theoutput coil has '>> turns. What is the reading on the voltmeter3

A@. S(>>@ C%

The input coil of a transformer has @>> turns of wire and is connected to a (A> B a.c. supply while the output coilas '(>> turns. What is the voltage across the output coil3

A=. S(>>Q C%The input voltage is (A> B. The input coil has @D>> turns and the output coil has '(> turns.6alculate the output voltage.

7elInduction

AD. S(>>Q!i" < resistor is connected in series with an ammeter and an ac power supply. < current flows in the circuit. The

resistor is then replaced with a coil. The resistance of the circuit does not change.What is the effect on the current flowing in the circuit3

!ii" ustify your answer

AQ. S(>>(!i" &n an experiment a coil was connected in series with an ammeter and an a.c. power

supply as shown in the diagram. Explain why the current was reduced when an ironcore was inserted in the coil.

!ii" Rive an application of the principle shown )y this experiment.

'>



E#am 7olutions

'. emf stands for electromotive force. &t is a potential difference applied to a full circuit.2! Electromagnetic &nduction occurs when an emf is induced in a coil due to a changing magnetic flux.>! Apparatus1 coil magnet and galvanometer.

rocedure1 5et up as shown.Move the magnet in and out of the coil.!bser"ation1 the needle deflects.

@.

!i" The needle in the galvanometer deflects.!ii" <n emf is induced in the coil of wire which in turn produces a current which moves the needle.!iii"There is a greater deflection of the needle.=.!i" 6orrect diagram to include magnet coil and meter!ii" Electromagnetic induction!iii" Oinetic to electric!iv"6urrent stopped whenever the magnet was motionless 88 electricity is only generated when the magnet or

coil is moving.D. Faraday$s %aw states that the si*e of the induced emf is proportional to the rate of change of flux.Q. %en*$s %aw states that the direction of the induced emf is always such as to oppose the change producing it.8! Faraday$s %aw states that the si*e of the induced emf is proportional to the rate of change of flux.

%en*$s %aw states that the direction of the induced emf is always such as to oppose the change producing it.

P. 5et up as shown.Move the magnet in and out of the coil and note the deflection in the galvanometer.

'>. Move the magnet in and out of the coil slowly and note a slight deflection.Move the magnet #uickly and note a greater deflection.

''.&i' 6urrent flows in the ring in such a direction as to oppose the change which caused it. Therefore the ring follows

the magnet.!ii" The ring would )e repelled.'(.

&i' <n emf is induced in the copper )ecause is its experiencing a changing magnetic field.This produces a current.This current has a magnetic field associated with it which opposes the motion of the magnet.

&ii' Oinetic !or potential" to electrical !or heat".'A.!i" <lternating current.!ii" There is no longer a full circuit so even though there is an induced potential difference there is no !induced"

current therefore no induced magnetic field in the coil therefore no opposing force.'@. Magnetic flux is defined as the product of magnetic flux density multiplied )y area.?;! #$0!d 8 dt"

# 4 =>>>! U '>-@ 8>.'" 4 @> B?<! E4 0 !d 8 dt" 4 !(>"S!(.A 7 '.@"8>.@

E 4 @= B'Q.&i' t 4 dist8velocity 4 = cm 8 =>> cm s -' 4 >.>' s&ii' K 4 ?< 4 !"!.>= U .>=" 4 >.>( we)ers.&iii' &nduced emf 4 !Final Flux 7&nitial Flux" 8 Time Taken

4 !> - >.>("8>.>' 4 ( Bolts

'.!i" < 4 !>.>="( 4 >.>>(=

!4 ?< " 4 !@"!>.>>(=" 4 >.>' W)

!ii" E 4 0!X8Xt"

X 8Xt 4 !>.>' 7 > "8>.( 4 >.>=E4 (>>!>.>=" ⇒ E 4 '> B

'P.!a" ?ecause only metal strings can )e magnitised.!)" ?ecause the induced emf varies due to the amplitude of the vi)rating string.

''



!c" < louder sound is produced.(>. B max 4 !Y("!Brms" ⇒ Brms4 A(=8Y( 4 (A> B('. %a)elled axes1 time on the hori*ontal and voltage on the vertical.22! <lternating current(A. !i" axes la)elled ! % and t "sinusoidal curve !at least one full wave"

!ii" !axes la)elled" correct curve(@. < diode is a device that allows current to flow in one direction only.(=. 2adio television computer )attery charger mo)ile phone charger.

(D. ;ynamo generator induction motor transformer dynamo

(Q. To increase or decrease voltage.(. 6omputer radio TB door)ell washing machine mo)ile phone chargers power supply etc.(P. < 4 primary 8 input coil ? 4 secondary 8 output coil 6 4 iron coreA>. &t has a laminated core.>?! '>V of the power in is lost.>2! Oinetic to electric.

AA. Bin8Bout 4 0input80output

(A>8Bout 4 @>>8'>>Bout 4 (A> U !'>>8@>>" 4 =Q.= Bolts

A@. Bin8Bout 4 0input80output

(A>8Bout 4 @>>8'(>>Bout 4 (A> U !@>>8'(>>" 4 DP> Bolts

A=. Bin8Bout 4 0input80output

(A>8Bout 4 @D>>8'(>Bout 4 (A> U !'(>8@D>>" 4 D Bolts

AD.&i' 6urrent is reduced&ii' <n emf is induced in the coil which induces a current which opposes the initial current.AQ.&i' There would normally )e a )ack emf in the coil due to the alternating current )eing supplied.

When the core was inserted it increased the magnetic flux which in turn increased the self-induction !)ack emf"and this reduced the overall voltage and therefore the overall current.

&ii' ;immer switch smooth d.c. tuning radios )raking trains damping in )alances induction coil

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28. Electromagnetic Induction (2)