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C H A P T E R 22Electromagnetic Induction

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Chapter 22Electromagnetic Induction

•Induced emf and Induced current

•Motional emf 

•Magnetic flux

•Faraday’s law of electromagnetic induction

•Lenz’s law

•pplications! cruise control" ground fault interrupter"

induction sto#e" electric guitar" microphone" $ spea%er&

•Electric generator 

•Inductance

•'ransformers and electric power transmission

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The Magnetic Playback Head of a

Tape Deck 

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A Moving Coil Microphone.

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22.7 The Electric Generator 

Electric generators such as these supply electrical power  (y

 producing an induced emf  according to Faraday)s law of

electromagnetic induction&

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Electric

Generator 

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Emf of the Generator 

'he induced emf is gi#en (y the following e*uation where" +is the num(er of turns in the coil" , is the magnetic field" is

the area of the coil" and - is the angular #elocity of the

rotation of the coil&

..&.///   t Sin NBA   ω ω ξ   =

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Self-inductance (L

'he alternating current in the coil generates an alternating

magnetic field that induces an emf  in the coil&

'he effect in which a changing current in a circuit induces an

emf in the same circuit is referred to as self-induction.

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!nit of Inductance

'he inductance"  L is measured in henries& 'he magnitude of

 L depends on the geometry of the coil and on the core

material&

,y wrapping the coil around a ferromagnetic /iron. core" the

magnetic flux and therefore the inductance can (e increased

su(stantially relati#e to that for an air core&

,ecause of their self0inductance" coils are %nown asinductors and are widely used in electronics&

Inductors come in all sizes" typically in the range (etween

millihenries and microhenries&

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22." Transformers

transformer  consists of a primary coil and a secondary coil" (oth

wound on an iron core& 'he changing magnetic flux produced (y

the current in the primary coil induces an emf  in the secondary

coil& t the far right is the sym(ol for a transformer&

transformer  is a de#ice for increasing or decreasing an ac

#oltage&

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#o$er Transmission

'ransformers play a %ey role in the transmission of

electric power &

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Transformer 

transformer consists of two coils" a primary and a secondary"

wound around a soft iron core

'he two coils are lin%ed (y the magnetic field&'he soft iron core will pro#ide a medium (y which the

magnetic flux from the primary coil is transferred to the

secondary coil&

'ransformers are designed so that nearly all the magnetic fluxfrom the primary coil is transferred to the secondary coil&

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Transformer E%uations

1sing Faraday’s law we can write expressions for the

 primary and secondary #oltages as follows&

&

t  N V 

S S 

∆

∆Φ=   &

t  N V 

 P  P 

∆

∆Φ=

&

 P 

S 

 P 

S 

 N  

 N  

V  

V  =

i#iding the a(o#e e*uations we get"

ssuming that there is no power loss" we can write"

&

 P  P S S   I V  I V    =

& P 

S 

S 

 P 

 P 

S 

 N 

 N 

 I 

 I 

V 

V ==

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#o$er Loss in Transmission Lines

 R I  P  Loss

2=