Magnetic Circuit

By,

Rohini HaridasAssistant Professor,

Dept of Electrical Engineering,

SSGM College of Engineering,Shegaon

UNIT -II

Magnetism Electromagnetism Electromagnetism Electromagnetic Induction

Magnet

• Magnet is an objectwhich possessesproperty of attractingiron and some othermetal pieces.metal pieces.

• When such a magnet is rolledinto iron pieces it will beobserved that :

• Maximum iron piecesaccumulate at the two ends ofthe magnet

• while very few accumulate atthe centre of the magnet.

• The points at which iron piecesaccumulate maximum arecalled poles.

When such amagnet issuspended freelyby the piece of silkfibre, it turns andalways adjustsalways adjustsitself in thedirection of Northand South.

Laws of MagnetismLaw 1 : It states that like magnetic poles repel and unlike magnetic poles attract each other

Law 2 :

It states that, the force (F) exerted by one pole on otherpole is,

i. Directly proportional to the product of pole strengths

ii. Inversely proportional to the square of the distanceii. Inversely proportional to the square of the distancebetween them

iii. Nature of medium surrounding the poles.

221

d

MMF

∗α

Magnetic Field

• The region around a magnet within which the influence of the magnet can be experienced is called magnetic field.

• Existence of such field can be experienced with the help pieces of metals.

Magnetic Lines of Force

• The magnetic field ofmagnet is represented byimaginary lines around itwhich are called magneticlines of force.lines of force.

• These lines have nophysical existence, theseare purely imaginary

Properties of lines of force1. Magnetic lines of force start from the North Pole and

end at the South Pole

2. They are continues through the body of magnet

3. Magnetic lines of force always prefer a path offering3. Magnetic lines of force always prefer a path offeringleast resistance.

4. Two magnetic lines of force can not intersect eachother.

5. They tend to contract in length

Magnetic Flux (φ)

• The total number of lines of force existing in a particular magnetic field is called magnetic flux.

• It is denoted by symbol (φ) and its unit is • It is denoted by symbol (φ) and its unit is weber is denoted as Wb.

1 Wb = lines of force810

Pole Strength

• The capacity of pole to supply or acceptcertain number of magnetic lines of force iscalled as its pole strength.

• Unit of pole strength is weber as pole strengthis directly related to flux i.e. lines of force

Magnetic Flux Density (B)

• The flux per unit area (a) in a plane at right angles to the flux is known as flux density.

Bφ=

• Unit is or Tesla

aB

φ=

2m

Wb

Magnetic Effect of Electric Current(Electromagnets)

• When a coil or a conductor carries a current, itproduces the magnetic flux around it.

• Then it starts behaving as a magnet. Such a• Then it starts behaving as a magnet. Such acurrent carrying coil or conductor is called anelectromagnet

• Flux produced can be controlled by controllingthe magnitude of current.

Cross & Dot Convention

Current INTO the plane of paper Current Coming Out of the plane of paper

*Current carrying conductor is represented by small circle

Right Hand Thumb Rule(Magnetic field due to current carrying conductor )

Grip the current carrying conductor in the right hand, with thethumb pointing in the direction of current, then the fingersencircling the conductor point in the direction of magnetic field

Representation of direction of flux