Sep 29, 2014

Permeability of Magnetic Circuit



The flow of flux created by the magnet not solely depends on the magnetic flux strength however conjointly on one vital property of the magnetic material is named permeability. It’s associated with the medium within which magnet is placed. The force exerted by one magnetic pole on different depends on the medium within which magnets are placed.

For any magnetic material, there are two types permeability. They are
  1. Absolute permeability
  2. Relative permeability

Absolute permeability (µ)

The magnetic field strength (H) decides the flux density (B) to be created by the magnet around it, in an exceedingly given medium- The magnitude relation of magnetic flux density B. In a specific medium (from vaccum or air) to the magnetic flux strength H producing that density is named absolute permeability of that medium.

It is denoted by µ and mathematically may be expressed as
                                          µ = B / H
                                         B = µ x H

The permeability is measured in units Henries per meter denoted as H/m.

Permeability of Free house or Vacuum (µo)

If the magnet is placed in an exceedingly free space or vacuum or in air then the magnitude relation of density B and magnetic field strength H is named permeability of free space or Vacuum or air.
It is denoted as µ0 and measured in H/m. It denotes the convenience with that the magnetic flux permeates the free house or vacuum or air.

It is by experimentation found that this µo i.e. magnitude relation of B and H in vacuum remains constant all over within the vacuum and its value is 4πx10-7 H/m.
                                   µ0=B/H in vacuum
                                   µ0= 4 π x 10-7 H/m
The ration of B to H is constant solely for free space, vaccum or air that is µo = 4π x 10-7 H/m.

Relative permeability (µr)

Generally the permeability of various magnetic materials is outlined relative to the permeableness of free space (µ0). The relative permeability is outlined because the magnitude relation of density created in an exceedingly medium (other than free space) to the density created in free space, underneath the influence of same magnetic field strength and underneath identical conditions.

Thus if the magnetic flux strength is H that is producing density B within the medium whereas density B0 in free space then the relative permeableness is outlined as,
µr=B/B0  Where “H” is same

It is dimensionless and has no units.
For free space, vaccum or air is µr=1

According to definition of absolute permeability we are able to write for given H,
µ = B/H in medium ------>1
µ0 = B0/H in free space ------->2
Dividing 1 & 2 we get
                                 µr=B/B0
                             ∵ µr= µ / µ0
                             ∴ µ= µr x µ0
The relative permeability of metals like Iron, Steel varies from 100 to 100,000 times.


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