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Permeability

State the meaning of permeability, write down the expression for the permeability of free space, and indciate how it was developed from the Biot-Savart Law.

Draw the B-H characteristic for:
a) a ferromagnetic material
b) a non-ferromagnetic material
and show how the permeability may be calculated from them.

Solution Preview

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SOLUTION

Before we discuss permeability, let us discuss the terms magnetic intensity (or magnetizing force) H and Magnetic induction (or magnetic flux density) B.

Magnetic intensity

It is the measure of the strength or intensity of the source (usually the current) that is causing the magnetic field. For example, when a current I is passed through a solenoid having n turns per meter, a magnetic field is produced with in the solenoid. This magnetic field is directly proportional to n and the magnitude of current I. Therefore, the product nI determines the magnitude of the magnetic field produced within the solenoid. Hence, for a solenoid, magnetic field strength H=nI.

Unit of H is Amperes/meter (A/m).

Magnetic induction

While magnetic intensity is the cause, magnetic induction is the effect. Thus, magnetic induction is the measure of the magnetic flux created by the magnetic intensity in a region. If the region is vacuum, the magnetic intensity H (cause) and the magnetic flux density B (effect) are related linearly.

Thus, for vacuum, B is directly proportional to H or B = μ0H where μ0 is the constant of proportionality known as the permeability of vacuum.

μ0 = B/H ...

Solution Summary

Magnetic intensity, magnetic induction, permeability etc. are explained in details.

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