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TERM PAPER

ELECTRICAL SCIENCE

ELE ( 101)Topic

USES OF MAGNETIC CIRCUIT

Submitted to submitted by

MR. GAGANDIP SIR Name .DHARMENDRA RAJ

Roll no :B33

Reg .NO.:10905576

Class ..B.tech -MBA(ME)

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ACKNOWLEDGEMENT

First of all I really thank my class teacher MR. GAGANDIP SIR for providing this maketerm

Paper . I have maked this termpaper with the help of internate, books, and

friend so I also thank

Fried for helping.

I also wish to express my appreciation for all my faculty members of ME department who

provided me time to time guidelines and help so that I could fulfill my term paper.

I would like to acknowledge a gratitude to my classmates who give me suggestions and

improvements to show my better efforts.

1*I want to give grateful thanks to my librarian who provided me related textbooks and refrence

books which increased my knowledge about books.

Last but not the least I would like to thank almighty who give me this opportunity.

Dharmendra Raj

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TABLE OF CONTENT

INTRODUCTION OF MAGNETIC CIRCUIT

1 Magnetomotive force (MMF)

2 Magnetic flux

3 Hopkinson's law: the magnetic analogy to Ohm's law

4 Reluctance 5 Microscopic origins of reluctance

6 Summary of analogy between magnetic circuits and electrical

circuits

7 Limitations of the analogy

8 Circuit Laws

9 History

10 Applications

LINES OF MAGNETIC FORCE

SOME IMAGES OF MAGNETIC CIRCUIT

11 References

http://en.wikipedia.org/wiki/Magnetic_circuit#Magnetomotive_force_.28MMF.29http://en.wikipedia.org/wiki/Magnetic_circuit#Magnetic_fluxhttp://en.wikipedia.org/wiki/Magnetic_circuit#Hopkinson.27s_law:_the_magnetic_analogy_to_Ohm.27s_lawhttp://en.wikipedia.org/wiki/Magnetic_circuit#Reluctancehttp://en.wikipedia.org/wiki/Magnetic_circuit#Microscopic_origins_of_reluctancehttp://en.wikipedia.org/wiki/Magnetic_circuit#Summary_of_analogy_between_magnetic_circuits_and_electrical_circuitshttp://en.wikipedia.org/wiki/Magnetic_circuit#Summary_of_analogy_between_magnetic_circuits_and_electrical_circuitshttp://en.wikipedia.org/wiki/Magnetic_circuit#Limitations_of_the_analogyhttp://en.wikipedia.org/wiki/Magnetic_circuit#Circuit_Lawshttp://en.wikipedia.org/wiki/Magnetic_circuit#Historyhttp://en.wikipedia.org/wiki/Magnetic_circuit#Applicationshttp://en.wikipedia.org/wiki/Magnetic_circuit#Referenceshttp://en.wikipedia.org/wiki/Magnetic_circuit#Magnetomotive_force_.28MMF.29http://en.wikipedia.org/wiki/Magnetic_circuit#Magnetic_fluxhttp://en.wikipedia.org/wiki/Magnetic_circuit#Hopkinson.27s_law:_the_magnetic_analogy_to_Ohm.27s_lawhttp://en.wikipedia.org/wiki/Magnetic_circuit#Reluctancehttp://en.wikipedia.org/wiki/Magnetic_circuit#Microscopic_origins_of_reluctancehttp://en.wikipedia.org/wiki/Magnetic_circuit#Summary_of_analogy_between_magnetic_circuits_and_electrical_circuitshttp://en.wikipedia.org/wiki/Magnetic_circuit#Summary_of_analogy_between_magnetic_circuits_and_electrical_circuitshttp://en.wikipedia.org/wiki/Magnetic_circuit#Limitations_of_the_analogyhttp://en.wikipedia.org/wiki/Magnetic_circuit#Circuit_Lawshttp://en.wikipedia.org/wiki/Magnetic_circuit#Historyhttp://en.wikipedia.org/wiki/Magnetic_circuit#Applicationshttp://en.wikipedia.org/wiki/Magnetic_circuit#References

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Magnetic circuit

A magnetic circuit is made up of one ormore closed loop paths containing a

magnetic flux. The flux is usually

generated by permanent magnets or

electromagnets and confined to the path by

magnetic cores consisting of ferromagnetic

materials like iron, although there may be

air gaps or other materials in the path.

Magnetic circuits are employed to

efficiently channel magnetic fields in

many devices such as electric motors,

generators, transformers, relays, liftingelectromagnets, SQUIDs, galvanometers,

and magnetic recording heads.

The concept of a "magnetic circuit"

exploits a one-to-one correspondence

between the equations of the magnetic

field in a non-hysteretic material to that of

an electrical circuit. Using this concept the

magnetic fields of complex devices such

as transformers can be quickly solved

using the methods and techniquesdeveloped for electrical circuits.

Some examples of magnetic circuits are:

horseshoe magnet with iron keeper

(low-reluctance circuit)

horseshoe magnet with no keeper

(high-reluctance circuit) electric motor (variable-reluctance

circuit)

Magnetomotive force(MMF)

Similar to the way, that EMF drives a

current of electrical charge in electricalcircuits, magnetomotive force (MMF)

'drives' magnetic flux through magnetic

circuits. The term 'magnetomotive force',

though, is a misnomer since it is not a

force nor is anything moving. It is perhaps

better to call it simply MMF. In analogy to

the definition ofEMF, the magnetomotive

force around a closed loop is defined as:

http://en.wikipedia.org/wiki/Magnetic_fluxhttp://en.wikipedia.org/wiki/Permanent_magnethttp://en.wikipedia.org/wiki/Electromagnethttp://en.wikipedia.org/wiki/Magnetic_corehttp://en.wikipedia.org/wiki/Magnetic_fieldhttp://en.wikipedia.org/wiki/Magnetic_fieldhttp://en.wikipedia.org/wiki/Electric_motorhttp://en.wikipedia.org/wiki/Transformerhttp://en.wikipedia.org/wiki/Relayhttp://en.wikipedia.org/wiki/Electromagnethttp://en.wikipedia.org/wiki/Galvanometerhttp://en.wikipedia.org/wiki/Recording_headhttp://en.wikipedia.org/wiki/Hysteresishttp://en.wikipedia.org/wiki/Electrical_circuithttp://en.wikipedia.org/wiki/Transformerhttp://en.wikipedia.org/wiki/Transformerhttp://en.wikipedia.org/wiki/Horseshoehttp://en.wikipedia.org/wiki/Magnethttp://en.wikipedia.org/wiki/Magnet_keeperhttp://en.wikipedia.org/wiki/Reluctancehttp://en.wikipedia.org/wiki/Electric_motorhttp://en.wikipedia.org/wiki/Electromotive_forcehttp://en.wikipedia.org/wiki/Magnetomotive_forcehttp://en.wikipedia.org/wiki/Electromotive_forcehttp://en.wikipedia.org/wiki/Magnetic_fluxhttp://en.wikipedia.org/wiki/Permanent_magnethttp://en.wikipedia.org/wiki/Electromagnethttp://en.wikipedia.org/wiki/Magnetic_corehttp://en.wikipedia.org/wiki/Magnetic_fieldhttp://en.wikipedia.org/wiki/Electric_motorhttp://en.wikipedia.org/wiki/Transformerhttp://en.wikipedia.org/wiki/Relayhttp://en.wikipedia.org/wiki/Electromagnethttp://en.wikipedia.org/wiki/Galvanometerhttp://en.wikipedia.org/wiki/Recording_headhttp://en.wikipedia.org/wiki/Hysteresishttp://en.wikipedia.org/wiki/Electrical_circuithttp://en.wikipedia.org/wiki/Transformerhttp://en.wikipedia.org/wiki/Horseshoehttp://en.wikipedia.org/wiki/Magnethttp://en.wikipedia.org/wiki/Magnet_keeperhttp://en.wikipedia.org/wiki/Reluctancehttp://en.wikipedia.org/wiki/Electric_motorhttp://en.wikipedia.org/wiki/Electromotive_forcehttp://en.wikipedia.org/wiki/Magnetomotive_forcehttp://en.wikipedia.org/wiki/Electromotive_force

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The MMF represents the potential that a

hypothetical magnetic charge would gain

by completing the loop. The magnetic flux

that is driven is not a current of magnetic

charge; it merely has the same relationship

to MMF that electrical current has to EMF.(See microscopic origins of reluctance

below for a further description.)

The unit of magnetomotive force is the

ampere-turn (At), represented by a steady,

direct electric current of one ampere

flowing in a single-turn loop of electrically

conducting material in a vacuum. The

gilbert (Gi), established by the IEC in

1930, is the CGS unit of magnetomotive

force and is a slightly smaller unit than theampere-turn. The unit is named after

William Gilbert (15441603) English

physician and natural philosopher.

The magnetomotive force can often be

quickly calculated using Ampere's law.

For example, the magnetomotive forceof long coil is:

,

whereNis the number ofturns andIis the

current in the coil. In practice this equation

is used for the MMF of real inductors with

N being the winding number of the

inducting coil

.

Magnetic flux

An applied MMF 'drives' magnetic flux

through the magnetic components of the

system. The magnetic flux through a

magnetic component is proportional to the

number of magnetic field lines that pass

through the cross sectional area of that

component. This is the netnumber, i.e. thenumber passing through in one direction,

minus the number passing through in the

other direction. The direction of the

magnetic field vectorB is by definition

from the south to the north pole of a

magnet inside the magnet; outside the field

lines go from north to south.

The flux through an element of area

perpendicular to the direction of magnetic

field is given by the product of the

magnetic field and the area element. More

generally, magnetic flux is defined by a

scalar product of the magnetic field and

the area element vector. Quantitatively, the

magnetic flux through a surface S is

defined as the integral of the magnetic

field over the area of the surface

For a magnetic component the area Sused

to calculate the magnetic flux is usually

chosen to be the cross-sectional area of the

component.

The SIunit of magnetic flux is the weber(in derived units: volt-seconds), and the

unit of magnetic field is the weber per

square meter, ortesla.

Hopkinson's law: the

magnetic analogy to Ohm's

law

In electronic circuits, Ohm's law is an

empirical relation between the EMF

applied across an element and the current I

it generates through that element. It is

written as:

where R is theelectrical resistance of that

material. Hopkinson's law is a counterpart

to Ohm's law used in magnetic circuits.

http://en.wikipedia.org/wiki/Magnetic_monopolehttp://en.wikipedia.org/wiki/Magnetic_monopolehttp://en.wikipedia.org/wiki/Ampere-turnhttp://en.wikipedia.org/wiki/Electric_currenthttp://en.wikipedia.org/wiki/Amperehttp://en.wikipedia.org/wiki/Amperehttp://en.wikipedia.org/wiki/Vacuumhttp://en.wikipedia.org/wiki/International_Electrotechnical_Commissionhttp://en.wikipedia.org/wiki/CGShttp://en.wikipedia.org/wiki/CGShttp://en.wikipedia.org/wiki/William_Gilberthttp://en.wikipedia.org/wiki/William_Gilberthttp://en.wikipedia.org/wiki/Ampere's_circuital_lawhttp://en.wikipedia.org/wiki/Turn_(geometry)http://en.wikipedia.org/wiki/Winding_numberhttp://en.wikipedia.org/wiki/Magnetic_fluxhttp://en.wikipedia.org/wiki/Magnetic_field#Magnetic_field_lineshttp://en.wikipedia.org/wiki/Fluxhttp://en.wikipedia.org/wiki/Areahttp://en.wikipedia.org/wiki/Perpendicularhttp://en.wikipedia.org/wiki/Perpendicularhttp://en.wikipedia.org/wiki/Magnetic_fieldhttp://en.wikipedia.org/wiki/Areahttp://en.wikipedia.org/wiki/Scalar_producthttp://en.wikipedia.org/wiki/Integralhttp://en.wikipedia.org/wiki/SIhttp://en.wikipedia.org/wiki/Unit_of_measurementhttp://en.wikipedia.org/wiki/Weber_(unit)http://en.wikipedia.org/wiki/Tesla_(unit)http://en.wikipedia.org/wiki/Electronic_circuitshttp://en.wikipedia.org/wiki/Ohm's_lawhttp://en.wikipedia.org/wiki/Electromotive_forcehttp://en.wikipedia.org/wiki/Electromotive_forcehttp://en.wikipedia.org/wiki/Electromotive_forcehttp://en.wikipedia.org/wiki/Current_(electricity)http://en.wikipedia.org/wiki/Electrical_resistancehttp://en.wikipedia.org/wiki/Electrical_resistancehttp://en.wikipedia.org/wiki/Ohm's_lawhttp://en.wikipedia.org/wiki/Magnetic_monopolehttp://en.wikipedia.org/wiki/Ampere-turnhttp://en.wikipedia.org/wiki/Electric_currenthttp://en.wikipedia.org/wiki/Amperehttp://en.wikipedia.org/wiki/Vacuumhttp://en.wikipedia.org/wiki/International_Electrotechnical_Commissionhttp://en.wikipedia.org/wiki/CGShttp://en.wikipedia.org/wiki/William_Gilberthttp://en.wikipedia.org/wiki/Ampere's_circuital_lawhttp://en.wikipedia.org/wiki/Turn_(geometry)http://en.wikipedia.org/wiki/Winding_numberhttp://en.wikipedia.org/wiki/Magnetic_fluxhttp://en.wikipedia.org/wiki/Magnetic_field#Magnetic_field_lineshttp://en.wikipedia.org/wiki/Fluxhttp://en.wikipedia.org/wiki/Areahttp://en.wikipedia.org/wiki/Perpendicularhttp://en.wikipedia.org/wiki/Magnetic_fieldhttp://en.wikipedia.org/wiki/Areahttp://en.wikipedia.org/wiki/Scalar_producthttp://en.wikipedia.org/wiki/Integralhttp://en.wikipedia.org/wiki/SIhttp://en.wikipedia.org/wiki/Unit_of_measurementhttp://en.wikipedia.org/wiki/Weber_(unit)http://en.wikipedia.org/wiki/Tesla_(unit)http://en.wikipedia.org/wiki/Electronic_circuitshttp://en.wikipedia.org/wiki/Ohm's_lawhttp://en.wikipedia.org/wiki/Electromotive_forcehttp://en.wikipedia.org/wiki/Current_(electricity)http://en.wikipedia.org/wiki/Electrical_resistancehttp://en.wikipedia.org/wiki/Ohm's_law

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The law is named after the British

electrical engineer, John Hopkinson. It

states that[1][2]

where is the magnetomotive force

(MMF) across a magnetic element, is the

magnetic flux through the magnetic

element, and is the magnetic reluctance

of that element. (It shall be shown later

that this relationship is due to the empirical

relationship between the H-field and the

magnetic field B, B=H, where is the

permeability of the material.) Like Ohm's

law, Hopkinson's law can be interpreted

either as an empirical equation that worksfor some materials, or it may serve as a

definition of reluctance.

Reluctance

Magnetic reluctance, or magnetic

resistance, is analogous to resistance in an

electrical circuit (although it does not

dissipate magnetic energy). In likeness to

the way an electric field causes anelectric

current to follow the path of least

resistance, a magnetic field causes

magnetic flux to follow the path of least

magnetic reluctance. It is a scalar,

extensive quantity, akin to electrical

resistance.

The total reluctance is equal to the ratio of

the (MMF) in a passive magnetic circuit

and the magnetic flux in this circuit. In an

AC field, the reluctance is the ratio of the

amplitude values for a sinusoidal MMF

and magnetic flux. (seephasors)

The definition can be expressed as:

where is the reluctance in ampere-turns

perweber(a unit that is equivalent to turns

perhenry).

Magnetic flux always forms a closed loop,

as described by Maxwell's equations, butthe path of the loop depends on the

reluctance of the surrounding materials. It

is concentrated around the path of least

reluctance. Air and vacuum have high

reluctance, while easily magnetized

materials such as soft iron have low

reluctance. The concentration of flux in

low-reluctance materials forms strong

temporary poles and causes mechanical

forces that tend to move the materials

towards regions of higher flux so it isalways an attractive force(pull).

The inverse of reluctance is called

permeance.

Its SI derived unit is the henry (the same as

the unit ofinductance, although the twoconcepts are distinct).

Microscopic origins ofreluctance

The reluctance of a magnetically uniformmagnetic circuit element can be calculated

as:

where

l is the length of the element in

metres

http://en.wikipedia.org/wiki/Electrical_engineerhttp://en.wikipedia.org/wiki/John_Hopkinsonhttp://en.wikipedia.org/wiki/Magnetic_circuit#cite_note-0http://en.wikipedia.org/wiki/Magnetic_circuit#cite_note-1http://en.wikipedia.org/wiki/Magnetic_fluxhttp://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Electrical_resistancehttp://en.wikipedia.org/wiki/Electricalhttp://en.wikipedia.org/wiki/Electrical_networkhttp://en.wikipedia.org/wiki/Electrical_networkhttp://en.wikipedia.org/wiki/Electric_fieldhttp://en.wikipedia.org/wiki/Electric_currenthttp://en.wikipedia.org/wiki/Electric_currenthttp://en.wikipedia.org/wiki/Electric_currenthttp://en.wikipedia.org/wiki/Magnetic_fieldhttp://en.wikipedia.org/wiki/Magnetic_fluxhttp://en.wikipedia.org/wiki/Scalar_(physics)http://en.wikipedia.org/wiki/Intensive_and_extensive_properties#Extensive_quantityhttp://en.wikipedia.org/wiki/Intensive_and_extensive_properties#Extensive_quantityhttp://en.wikipedia.org/wiki/Magnetic_fluxhttp://en.wikipedia.org/wiki/Phasor_(sine_waves)http://en.wikipedia.org/wiki/Ampere-turnhttp://en.wikipedia.org/wiki/Weber_(unit)http://en.wikipedia.org/wiki/Weber_(unit)http://en.wikipedia.org/wiki/Henry_(unit)http://en.wikipedia.org/wiki/Maxwell's_equationshttp://en.wikipedia.org/wiki/Soft_ironhttp://en.wikipedia.org/wiki/Permeancehttp://en.wikipedia.org/wiki/Permeancehttp://en.wikipedia.org/wiki/SIhttp://en.wikipedia.org/wiki/Henry_(unit)http://en.wikipedia.org/wiki/Inductancehttp://en.wikipedia.org/wiki/Metrehttp://en.wikipedia.org/wiki/Electrical_engineerhttp://en.wikipedia.org/wiki/John_Hopkinsonhttp://en.wikipedia.org/wiki/Magnetic_circuit#cite_note-0http://en.wikipedia.org/wiki/Magnetic_circuit#cite_note-1http://en.wikipedia.org/wiki/Magnetic_fluxhttp://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Electrical_resistancehttp://en.wikipedia.org/wiki/Electricalhttp://en.wikipedia.org/wiki/Electrical_networkhttp://en.wikipedia.org/wiki/Electric_fieldhttp://en.wikipedia.org/wiki/Electric_currenthttp://en.wikipedia.org/wiki/Electric_currenthttp://en.wikipedia.org/wiki/Magnetic_fieldhttp://en.wikipedia.org/wiki/Magnetic_fluxhttp://en.wikipedia.org/wiki/Scalar_(physics)http://en.wikipedia.org/wiki/Intensive_and_extensive_properties#Extensive_quantityhttp://en.wikipedia.org/wiki/Magnetic_fluxhttp://en.wikipedia.org/wiki/Phasor_(sine_waves)http://en.wikipedia.org/wiki/Ampere-turnhttp://en.wikipedia.org/wiki/Weber_(unit)http://en.wikipedia.org/wiki/Henry_(unit)http://en.wikipedia.org/wiki/Maxwell's_equationshttp://en.wikipedia.org/wiki/Soft_ironhttp://en.wikipedia.org/wiki/Permeancehttp://en.wikipedia.org/wiki/SIhttp://en.wikipedia.org/wiki/Henry_(unit)http://en.wikipedia.org/wiki/Inductancehttp://en.wikipedia.org/wiki/Metre

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= r0 is the permeability of the

material (r is the relative

permeability of the material

(dimensionless), and 0 is the

permeability of free space)

A is the cross-sectional area of thecircuit in square metres

This is similar to the equation for electrical

resistance in materials, with permeability

being analogous to conductivity; the

reciprocal of the permeability is known as

magnetic reluctivity and is analogous to

resistivity. Longer, thinner geometries

with low permeabilities lead to higher

reluctance. Low reluctance, like low

resistance in electric circuits, is generallypreferred.

Summary of analogy

between magnetic circuits

and electrical circuits

The following table summarizes the

mathematical analogy between electrical

circuit theory and magnetic circuit theory.

This is mathematical analogy and not a

physical one. Objects in the same row

have the same mathematical role; the

physics of the two theories are very

different. For example, current is the flow

of electrical charge, while magnetic flux is

not the flow of any quantity.

Analogy between 'magnetic circuits' and

electrical circuits

Magneti

c

equivale

nt

Symbol Units

Electri

c

equiva

lent

Symbol

Magnet

omotive

force(MMF)

ampere

-turn

Defini

tion of

EMF

H-field Hampere

/meter

Electri

c fieldE

Magneti

c flux weber

Electri

c

Curre

nt

I

Hopkins

on's

Law

Ohm's

Law

Relucta

nceHenry

Electri

cal

resista

nce

R

relation

between

B and H

Micro

scopic

Ohm'sLaw

Magneti

c fieldBB tesla

Curre

nt

densit

y

J

permeab

ility

Henry/

meter

Electri

cal

condu

ctivity

Limitations of the analogy

When using the analogy between magnetic

circuits and electric circuits, the limitations

of this analogy must be kept in mind.

Electric and magnetic circuits are only

superficially similar because of the

similarity between Hopkinson's law and

Ohm's law. Magnetic circuits have

significant differences, which must be

taken into account in their construction:

Electric currents represent the flow

of particles (electrons) and carry

power, which is dissipated as heat

in resistances. Magnetic fields don't

represent the "flow" of anything,

and no power is dissipated in

reluctances.

http://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Square_metrehttp://en.wikipedia.org/wiki/Ampere-turnhttp://en.wikipedia.org/wiki/Ampere-turnhttp://en.wikipedia.org/wiki/Magnetic_fieldhttp://en.wikipedia.org/wiki/Amperehttp://en.wikipedia.org/wiki/Meterhttp://en.wikipedia.org/wiki/Electric_fieldhttp://en.wikipedia.org/wiki/Electric_fieldhttp://en.wikipedia.org/wiki/Weber_(unit)http://en.wikipedia.org/wiki/Electric_Currenthttp://en.wikipedia.org/wiki/Electric_Currenthttp://en.wikipedia.org/wiki/Electric_Currenthttp://en.wikipedia.org/wiki/Electric_Currenthttp://en.wikipedia.org/wiki/Ohm's_Lawhttp://en.wikipedia.org/wiki/Ohm's_Lawhttp://en.wikipedia.org/wiki/Reluctancehttp://en.wikipedia.org/wiki/Reluctancehttp://en.wikipedia.org/wiki/Henry_(unit)http://en.wikipedia.org/wiki/Electrical_resistancehttp://en.wikipedia.org/wiki/Electrical_resistancehttp://en.wikipedia.org/wiki/Electrical_resistancehttp://en.wikipedia.org/wiki/Electrical_resistancehttp://en.wikipedia.org/wiki/Magnetic_fieldhttp://en.wikipedia.org/wiki/Magnetic_fieldhttp://en.wikipedia.org/wiki/Teslahttp://en.wikipedia.org/wiki/Current_densityhttp://en.wikipedia.org/wiki/Current_densityhttp://en.wikipedia.org/wiki/Current_densityhttp://en.wikipedia.org/wiki/Current_densityhttp://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Henry_(unit)http://en.wikipedia.org/wiki/Meterhttp://en.wikipedia.org/wiki/Electrical_conductivityhttp://en.wikipedia.org/wiki/Electrical_conductivityhttp://en.wikipedia.org/wiki/Electrical_conductivityhttp://en.wikipedia.org/wiki/Electrical_conductivityhttp://en.wikipedia.org/wiki/Power_(physics)http://en.wikipedia.org/wiki/Power_(physics)http://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Square_metrehttp://en.wikipedia.org/wiki/Ampere-turnhttp://en.wikipedia.org/wiki/Ampere-turnhttp://en.wikipedia.org/wiki/Magnetic_fieldhttp://en.wikipedia.org/wiki/Amperehttp://en.wikipedia.org/wiki/Meterhttp://en.wikipedia.org/wiki/Electric_fieldhttp://en.wikipedia.org/wiki/Electric_fieldhttp://en.wikipedia.org/wiki/Weber_(unit)http://en.wikipedia.org/wiki/Electric_Currenthttp://en.wikipedia.org/wiki/Electric_Currenthttp://en.wikipedia.org/wiki/Electric_Currenthttp://en.wikipedia.org/wiki/Ohm's_Lawhttp://en.wikipedia.org/wiki/Ohm's_Lawhttp://en.wikipedia.org/wiki/Reluctancehttp://en.wikipedia.org/wiki/Reluctancehttp://en.wikipedia.org/wiki/Henry_(unit)http://en.wikipedia.org/wiki/Electrical_resistancehttp://en.wikipedia.org/wiki/Electrical_resistancehttp://en.wikipedia.org/wiki/Electrical_resistancehttp://en.wikipedia.org/wiki/Magnetic_fieldhttp://en.wikipedia.org/wiki/Magnetic_fieldhttp://en.wikipedia.org/wiki/Teslahttp://en.wikipedia.org/wiki/Current_densityhttp://en.wikipedia.org/wiki/Current_densityhttp://en.wikipedia.org/wiki/Current_densityhttp://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Permeability_(electromagnetism)http://en.wikipedia.org/wiki/Henry_(unit)http://en.wikipedia.org/wiki/Meterhttp://en.wikipedia.org/wiki/Electrical_conductivityhttp://en.wikipedia.org/wiki/Electrical_conductivityhttp://en.wikipedia.org/wiki/Electrical_conductivityhttp://en.wikipedia.org/wiki/Power_(physics)

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The current in typical electric

circuits is confined to the circuit,

with very little "leakage". In typical

magnetic circuits not all of the

magnetic field is confined to the

magnetic circuit; there issignificant "leakage flux" in the

space outside the magnetic cores,

which must be taken into account

but is difficult to calculate.

Most importantly, magnetic

circuits are nonlinear; the

reluctance in a magnetic circuit is

not constant, as resistance is, but

varies depending on the magnetic

field. At high magnetic fluxes the

ferromagnetic materials used forthe cores of magnetic circuits

saturate, limiting the magnetic flux,

so above this level the reluctance

increases rapidly. The reluctance

also increases at low fluxes. In

addition, ferromagnetic materials

suffer from hysteresis so the flux in

them depends not just on the

instantaneous MMF but also on the

past history of MMF. After the

source of the magnetic flux is

turned off, remanent magnetism is

left in ferromagnetic circuits,

creating a flux with no MMF.

Circuit Laws

Magnetic circuit

Magnetic circuits obey other laws that are

similar to electrical circuit laws. For

example, the total reluctance of

reluctances in series is:

This also follows from Ampre's law and

is analogous to Kirchhoff's voltage law for

adding resistances in series. Also, the sum

of magnetic fluxes into any node

is always zero:

This follows from Gauss's law and is

analogous to Kirchhoff's current law for

analyzing electrical circuits.

Together, the three laws above form a

complete system for analysing magnetic

circuits, in a manner similar to electric

circuits. Comparing the two types of

circuits shows that:

The equivalent to resistance R is

the reluctanceRm The equivalent to current I is the

magnetic flux

http://en.wikipedia.org/wiki/Leakage_fluxhttp://en.wikipedia.org/wiki/Nonlinear_elementhttp://en.wikipedia.org/wiki/Ferromagnetic_materialshttp://en.wikipedia.org/wiki/Saturation_(magnetic)http://en.wikipedia.org/wiki/Saturation_(magnetic)http://en.wikipedia.org/wiki/Hysteresishttp://en.wikipedia.org/wiki/Remanent_magnetismhttp://en.wikipedia.org/wiki/Remanent_magnetismhttp://en.wikipedia.org/wiki/Amp%C3%A8re's_lawhttp://en.wikipedia.org/wiki/Amp%C3%A8re's_lawhttp://en.wikipedia.org/wiki/Kirchhoff's_circuit_lawshttp://en.wikipedia.org/wiki/Gauss's_lawhttp://en.wikipedia.org/wiki/Kirchhoff's_circuit_lawshttp://en.wikipedia.org/wiki/Kirchhoff's_circuit_lawshttp://en.wikipedia.org/wiki/File:Magnetischer_Kreis.svghttp://en.wikipedia.org/wiki/Leakage_fluxhttp://en.wikipedia.org/wiki/Nonlinear_elementhttp://en.wikipedia.org/wiki/Ferromagnetic_materialshttp://en.wikipedia.org/wiki/Saturation_(magnetic)http://en.wikipedia.org/wiki/Hysteresishttp://en.wikipedia.org/wiki/Remanent_magnetismhttp://en.wikipedia.org/wiki/Amp%C3%A8re's_lawhttp://en.wikipedia.org/wiki/Kirchhoff's_circuit_lawshttp://en.wikipedia.org/wiki/Gauss's_lawhttp://en.wikipedia.org/wiki/Kirchhoff's_circuit_laws

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The equivalent to voltage V is the

magnetomotive ForceF

Magnetic circuits can be solved for theflux in each branch by application of the

magnetic equivalent of Kirchhoff's

Voltage Law (KVL) for pure

source/resistance circuits. Specifically,

whereas KVL states that the voltage

excitation applied to a loop is equal to the

sum of the voltage drops (resistance times

current) around the loop, the magnetic

analogue states that the magnetomotive

force (achieved from ampere-turn

excitation) is equal to the sum of MMFdrops (product of flux and reluctance)

across the rest of the loop. (If there are

multiple loops, the current in each branch

can be solved through a matrix equation

much as a matrix solution for mesh circuit

branch currents is obtained in loop

analysisafter which the individual

branch currents are obtained by adding

and/or subtracting the constituent loop

currents as indicated by the adopted sign

convention and loop orientations.) Per

Ampre's law, the excitation is the product

of the current and the number of complete

loops made and is measured in ampere-

turns. Stated more generally:

(Note that, per Stokes's theorem, the

closed line integral of H dot dl around acontour is equal to the open surface

integral of curl H dot dA across the surface

bounded by the closed contour. Since,

fromMaxwell's equations, curlH = J, the

closed line integral of H dot dl evaluates to

the total current passing through the

surface. This is equal to the excitation, NI,

which also measures current passing

through the surface, thereby verifying that

the net current flow through a surface is

zero ampere-turns in a closed system thatconserves energy.)

More complex magnetic systems, where

the flux is not confined to a simple loop,

must be analysed from first principles by

using Maxwell's equations.

History Magnetic circuit

The term reluctance was coined in

May 1888 by Oliver Heaviside. The

notion of magnetic resistance was

first mentioned by James Joule andthe term "magnetomotive force

(MMF) was first named by

Bosanquet. The idea for a magnetic

flux law, similar to Ohm's law for

closed electric circuits, is attributed

to H. Rowland

Applications of Magneticcircuit

Air gaps can be created in the cores

of certain transformers to reduce

the effects ofsaturation. This

increases the reluctance of the

magnetic circuit, and enables it tostore more energy before core

saturation. This effect is also used

in the flyback transformer.

Variation of reluctance is the

principle behind the reluctance

motor(or the variable reluctance

generator) and theAlexanderson

alternator.

Multimedia loudspeakers aretypically shielded magnetically, in

http://en.wikipedia.org/wiki/Kirchhoff's_circuit_lawshttp://en.wikipedia.org/wiki/Kirchhoff's_circuit_lawshttp://en.wikipedia.org/wiki/KVLhttp://en.wikipedia.org/wiki/Amp%C3%A8re's_lawhttp://en.wikipedia.org/wiki/Amp%C3%A8re's_lawhttp://en.wikipedia.org/wiki/Line_integralhttp://en.wikipedia.org/wiki/Surface_integralhttp://en.wikipedia.org/wiki/Surface_integralhttp://en.wikipedia.org/wiki/Maxwell's_equationshttp://en.wikipedia.org/wiki/Maxwell's_equationshttp://en.wikipedia.org/wiki/Maxwell's_equationshttp://en.wikipedia.org/wiki/Curl_(mathematics)http://en.wikipedia.org/wiki/Curl_(mathematics)http://en.wikipedia.org/wiki/Curl_(mathematics)http://en.wikipedia.org/wiki/Maxwell's_equationshttp://en.wikipedia.org/wiki/Oliver_Heavisidehttp://en.wikipedia.org/wiki/James_Joulehttp://en.wikipedia.org/wiki/Magnetomotive_forcehttp://en.wikipedia.org/wiki/Magnetic_fluxhttp://en.wikipedia.org/wiki/Magnetic_fluxhttp://en.wikipedia.org/wiki/Ohm's_lawhttp://en.wikipedia.org/wiki/Electric_circuithttp://en.wikipedia.org/wiki/Henry_Augustus_Rowlandhttp://en.wikipedia.org/wiki/Saturation_(magnetic)http://en.wikipedia.org/wiki/Saturation_(magnetic)http://en.wikipedia.org/wiki/Energyhttp://en.wikipedia.org/wiki/Flyback_transformerhttp://en.wikipedia.org/wiki/Flyback_transformerhttp://en.wikipedia.org/wiki/Reluctance_motorhttp://en.wikipedia.org/wiki/Reluctance_motorhttp://en.wikipedia.org/wiki/Alexanderson_alternatorhttp://en.wikipedia.org/wiki/Alexanderson_alternatorhttp://en.wikipedia.org/wiki/Alexanderson_alternatorhttp://en.wikipedia.org/wiki/Alexanderson_alternatorhttp://en.wikipedia.org/wiki/Multimediahttp://en.wikipedia.org/wiki/Loudspeakerhttp://en.wikipedia.org/wiki/Kirchhoff's_circuit_lawshttp://en.wikipedia.org/wiki/Kirchhoff's_circuit_lawshttp://en.wikipedia.org/wiki/KVLhttp://en.wikipedia.org/wiki/Amp%C3%A8re's_lawhttp://en.wikipedia.org/wiki/Line_integralhttp://en.wikipedia.org/wiki/Surface_integralhttp://en.wikipedia.org/wiki/Surface_integralhttp://en.wikipedia.org/wiki/Maxwell's_equationshttp://en.wikipedia.org/wiki/Curl_(mathematics)http://en.wikipedia.org/wiki/Maxwell's_equationshttp://en.wikipedia.org/wiki/Oliver_Heavisidehttp://en.wikipedia.org/wiki/James_Joulehttp://en.wikipedia.org/wiki/Magnetomotive_forcehttp://en.wikipedia.org/wiki/Magnetic_fluxhttp://en.wikipedia.org/wiki/Magnetic_fluxhttp://en.wikipedia.org/wiki/Ohm's_lawhttp://en.wikipedia.org/wiki/Electric_circuithttp://en.wikipedia.org/wiki/Henry_Augustus_Rowlandhttp://en.wikipedia.org/wiki/Saturation_(magnetic)http://en.wikipedia.org/wiki/Energyhttp://en.wikipedia.org/wiki/Flyback_transformerhttp://en.wikipedia.org/wiki/Reluctance_motorhttp://en.wikipedia.org/wiki/Reluctance_motorhttp://en.wikipedia.org/wiki/Alexanderson_alternatorhttp://en.wikipedia.org/wiki/Alexanderson_alternatorhttp://en.wikipedia.org/wiki/Multimediahttp://en.wikipedia.org/wiki/Loudspeaker

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order to reduce magnetic

interference caused to televisions

and otherCRTs. The speaker

magnet is covered with a material

such as soft iron to minimize the

stray magnetic field.

Reluctance can also be applied to:

Reluctance motors

Variable reluctance (magnetic)

pickups

Lines of Magnetic Force

Features of Lines of

Flux

There are several characteristics of

lines of force which are as follows.

Direction: any line of flux always

points towards the north seeking pole

of a magnet provided it is not under the

influence of another magnetic medium

except the magnetic field of the earth.

Closed Line: all lines of flux form a

closed loop which emerge from the

North Pole into the South Pole of the

magnet

Independent Region: lines of flux

never intersect each other.

Repulsion: lines of flux which are in the

same direction always repel

each other

SOME IMAGES OF MAGNETIC CIRCUIT

http://en.wikipedia.org/wiki/Televisionhttp://en.wikipedia.org/wiki/Cathode_ray_tubehttp://en.wikipedia.org/wiki/Soft_ironhttp://en.wikipedia.org/wiki/Electric_motorhttp://en.wikipedia.org/wiki/Pick_up_(music_technology)http://www.brighthub.com/engineering/electrical/articles/3829.aspx?image=42731http://en.wikipedia.org/wiki/Televisionhttp://en.wikipedia.org/wiki/Cathode_ray_tubehttp://en.wikipedia.org/wiki/Soft_ironhttp://en.wikipedia.org/wiki/Electric_motorhttp://en.wikipedia.org/wiki/Pick_up_(music_technology)

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REFERENCES:

WWW.ANSWER.COM

WWW.1000.COM

WWW.ELECTRICAL.COM

http://www.google.co.in/#hl=en&source=hp&q=MAGNETIC+CIRCUIT&meta=&aq=o&aqi

=&aql=&oq=&gs_rfai=&fp=52ac89d4f1717d11

http://en.wikipedia.org/wiki/Circuit_breaker

http://www.next.gr/sens-detectors/magnetic-circuits/

book:

Electrical science by j.b gupta

Electrical science by john hiley,keith brown

http://www.answer.com/http://www.1000.com/http://www.electrical.com/http://www.google.co.in/#hl=en&source=hp&q=MAGNETIC+CIRCUIT&meta=&aq=o&aqi=&aql=&oq=&gs_rfai=&fp=52ac89d4f1717d11http://www.google.co.in/#hl=en&source=hp&q=MAGNETIC+CIRCUIT&meta=&aq=o&aqi=&aql=&oq=&gs_rfai=&fp=52ac89d4f1717d11http://en.wikipedia.org/wiki/Circuit_breakerhttp://www.next.gr/sens-detectors/magnetic-circuits/http://www.answer.com/http://www.1000.com/http://www.electrical.com/http://www.google.co.in/#hl=en&source=hp&q=MAGNETIC+CIRCUIT&meta=&aq=o&aqi=&aql=&oq=&gs_rfai=&fp=52ac89d4f1717d11http://www.google.co.in/#hl=en&source=hp&q=MAGNETIC+CIRCUIT&meta=&aq=o&aqi=&aql=&oq=&gs_rfai=&fp=52ac89d4f1717d11http://en.wikipedia.org/wiki/Circuit_breakerhttp://www.next.gr/sens-detectors/magnetic-circuits/