CHAPTER-4

MAGNETISM

CONTENT

1. Basic definition of flux, m.m.f, reluctance, relation between B,H,I.

2. Comparison between electric and magnetic circuits.

What is a MAGNET?

A magnet (from Greek magnḗtis líthos) is a material or

object that produces a magnetic field. This magnetic field is invisible

but is responsible for the most notable property of a magnet: a force

that pulls on other ferromagnetic materials, such as iron, and attracts

or repels other magnets.

What is Magnetic Field?

A region around a magnetic material or a moving electric

charge within which the force of magnetism acts.

What is Magnetic Flux?

Magnetic flux (most often denoted as Φ), is the amount of

magnetic field passing through a surface (such as a conducting coil).

The SI unit of magnetic flux is the weber (Wb)

What is Magnetic Flux Density?

Magnetic flux density is the amount of magnetic flux per unit

area of a section that is perpendicular to the direction of flux.

Mathematically it is represented as

The SI unit for magnetic flux density is the tesla.

What is M.M.F?

Magneto motive force, also known as magnetic potential, is

the property of certain substances or phenomena that gives rise to

magnetic field. Magneto motive force is analogous to electromotive force

or voltage in electricity.

The standard unit of magneto motive force is the ampere-turn (AT).

What is Reluctance?

The property of a magnetic circuit of opposing the passage

of magnetic flux lines, equal to the ratio of the magneto motive force to

the magnetic flux.

Magnetic reluctance or magnetic resistance.

It is analogous to resistance in an electrical circuit.

The unit for magnetic reluctance is inverse henry, H−1.

What is Reluctance?

Intensity of magnetising field (H)

Magnetising Field Intensity or magnetic intensity (H)

The degree to which a magnetic field can magnetize a material is called

magnetic field or magnetizing force or Magnetic Intensity.

OR

The number of ampere-turns (nI) per unit length of a solenoid required to

produce a given magnetising field

H is measured in Ampere/meter(A/m).

Intensity of Magnetization (I)

Intensity of magnetization is defined as the magnetic moment

per unit volume of the magnetized material.

I=

where M is the total magnetic moment within volume V due to the

magnetizing field

Unit of I is A/m (Ampere/meter).

Susceptibility(K)

It is defined as the ratio of intensity of magnetization (I) to the

magnetizing field intensity (H) applied

K = Henry/metre

Relation between B,H,I & K

Permeability of free space (μ0)

Comparison between Electric and

Magnetic circuits

Similarities

Differences

END