What is [Electromagnetism] And How Does It Work | 3 Types Of Magnetic Material

ElectroMagnetism

Elec­tro­Mag­net­ism has attained a place of pride in elec­tri­cal engi­neer­ing. With­out the aid of mag­net­ism it is impos­si­ble to oper­ate such devices as elec­tric generators,electric motors,transformers,electric instruments. 

With­out the use of mag­net­ism we should be deprived of such valu­able assets as the radio, tele­vi­sion, tele­phone, tele­graph and igni­tion sys­tem of our cars, aero­plane, trucks. The pur­pose of this chap­ter is to present the salient fea­tures of mag­net­ism so that a read­er may be able to under­stand the func­tion of Elec­tro­Mag­net­ism in elec­tic equipments 

Magnetic Material

1.Ferro mag­net­ic materials 

2.Para Mag­net­ic Materials 

3.Dia Mag­net­ic Materials 

1.Ferro Magnetic Material 

The mate­ri­als pos­sess­ing high­er degree of mag­net­ic prop­er­ties are called Fer­ro Mag­net­ic Mate­ri­als these mate­ri­als are strong­ly attract­ed by the magnets 

Exam­ple= Iron, Nick­el, Cobalt,Alloy

2.Para Magnetic Materials 

Mate­ri­als hav­ing slight Mag­net­ic prop­er­ties are called para Mag­net­ic Mate­ri­als. They are attached by the mag­net slightly 

Example=Platinum,manganese, aluminium,tin, cop­per sulphate,ferric chloride 

3.Dia Magnetic Materials 

Mate­ri­als hav­ing Mag­net­ic prop­er­ties which are less than fer­ro and para Mag­net­ic Mate­ri­als are called dia­mag­net­ic mate­ri­als. Dia Mag­net­ic Mate­ri­als are repelled by the magnet 

Example=Antimony,Bismuth,Glass, Mer­cury, Gold, Cop­per, Sodi­um chlo­ride, Lead etc 

What is ElectroMagnet

The mate­r­i­al used for elec­tro mag­net is soft iron or soft steel with a few per­cent­age of sil­i­con. A coil of insu­lat­ed wire is wound on a soft iron 

They exhib­it strong mag­net­ism so long as there is a flow of cur­rent through the coil when there is no cur­rent through the coil the core loss it’s mag­net­ism. These type of mag­nets are called electromagnet 

Uses of ElectroMagnet 

Elec­tro mag­nets are used in Elec­tric Gen­er­a­tors, Motors,relays,Electric bells 

What is Permanent Magnet 

The mag­net which retains the mag­nat­ic prop­er­ties for a long peri­od is known as per­ma­nent mag­net. Alu­mini­um, Nickel,Iron,Cobalt is the most impor­tant hard mate­ri­als used for mak­ing per­ma­nent mag­net. The per­ma­nent mag­nets avail­able in dif­fer­ent shapes 

Bar magnet

U‑Shaped Magnet

Per­ma­nent mag­nets are made by instruc­tion process. This is done by wind­ing a coil over the piece of steel to be mag­ne­tised and pass­ing a large D.C cur­rent through the coil. When the cur­rent flows through the coil the steel piece is mag­ne­tised. If the cur­rent is stopped a major por­tion of the mag­net­ism is retained and it becomes per­ma­nent mag­net. The mag­net­ism retained by the steel after the remov­ing of mag­netis­ing force is called the resid­ual magnetism 

Uses of Permanent Magnet 

Per­ma­nent mag­nets are used in elec­tri­cal mea­sur­ing Instruments,magnetic Chuck­’s, speak­ers and cycle dynamos 

What is Magnetic Field 

The region around a per­ma­nent mag­net or the space around a cur­rent car­ry­ing con­duc­tor occu­pied by the lines of force is called the mag­nat­ic field of force or mag­nat­ic field 

What is Magnetic Flux 

The amount of mag­nat­ic lines of force in a mag­nat­ic field known as Mag­net­ic Flux 

These Flux lines from a closed path and the path fol­lowed by the flux lines is known as Mag­net­ic cir­cuit. The unit of mag­net­ic flux is Weber and is rep­re­sent­ed by the let­ter Φ 

What is Magnetic Flux Density 

The flux den­si­ty is the mag­nat­ic flux per unit area tak­en per­pen­dic­u­lar to the direc­tion of the mag­nat­ic flux 

It is usu­al­ly denot­ed by the let­ter, B and its unit in Tes­la . If a flux of Φ Weber is pass­ing through an area of ‘A’ square matre,then the flux den­si­ty B is giv­en by B=Φ/A web/square meter 

What is Permeability 

The flow of flux pro­duced by the Mag­net not only depends on the mag­nat­ic field strength but also depends an one impor­tant prop­er­ty. It is relat­ed to the medi­um in which mag­net is placed 

The per­me­abil­i­ty is defined as the abil­i­ty in which the mag­nat­ic mate­r­i­al forces the mag­nat­ic flux through a giv­en medium 

There are two types of permeabilitys 

1.Absolute permeability 

2.Relative permeability 

Absolute permeability

The mag­nat­ic field strength decides the flux den­si­ty to be pro­duced by the Mag­net around it in a giv­en medium 

The ratio of mag­nat­ic flux den­si­ty in a par­tic­u­lar medi­um to the mag­nat­ic field strength pro­duc­ing that mag­nat­ic flux den­si­ty is called absolute per­me­abil­i­ty of that medi­um. It is denot­ed by µ 

µ = B/H

Relative Permeability

The rel­a­tive per­me­abil­i­ty is defined as the ratio of flux den­si­ty pro­duced in a medi­um to the flux den­si­ty pro­duced in free strength and under iden­ti­cal conditions 

If the mag­nat­ic field strength H pro­duc­ing a flux den­si­ty B in the medi­um while flux den­si­ty Bo in free space then the rel­a­tive per­me­abil­i­ty is 

µr=B/BO

What is MMF (MAGNETO MOTIVE FORCE) 

The force which estab­lish­es the mag­nat­ic flux in a mag­nat­ic cir­cuit is called Mag­ne­to motive force. It cor­re­sponds to elec­tro motive force in an elec­tric circuit. 

The Mag­ne­to motive force is pro­duced when a cur­rent pass­es through a coil of wire. The mmf is the prod­uct of the num­ber of turns of the coil and the cur­rent through the coil. 

The unit of mmf is Ampere turns and it is rep­re­sent­ed by a let­ter F. If a cur­rent of I ampere is flow­ing through a coil of N turns the m.m.f. pro­duced is equal to 

F= NI ampere turns 

Ampere turns is the unit of mag­ne­to motive force The ampere turns of a mag­nat­ic cir­cuit are giv­en by the prod­uct of the turns of the coil and the amperes in the coil 

Ampere turns = NI 

What is Reluctance 

Reluc­tance is the prop­er­ty of a mate­r­i­al which oppos­es the estab­lish­ment of mag­nat­ic flux in it. It is the resis­tance offered to the pas­sage of mag­nat­ic flux through a material 

Reluc­tance = mmf/Φ

Reluc­tance unit is AT/WB

What is Magnetic Field Strength 

The Mag­ne­to motive force per unit length of the mag­nat­ic cir­cuit is termed as Mag­net­ic field inten­si­ty. The mag­nat­ic field inten­si­ty is denot­ed by the let­ter H and it’s unit is Ampere turns/meter. It is also known as mag­netis­ing force or mag­nat­ic field strength 

H = NI/ℓ

H = mag­netis­ing force 

I = cur­rent through the coil,in Amperes 

ℓ=length of the mag­nat­ic cir­cuit in meters 

What is Permeance 

It is the rec­i­p­ro­cal of reluc­tance. It cor­re­sponds to in elec­tric cir­cuits. Its unit is web/AT

Per­me­ance = 1/Reluctance web/AT

What is Reluctivity 

It is spe­cif­ic reluc­tance and cor­re­sponds to resis­tiv­i­ty in elec­tic circuit. 

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