Ohm’s law and its derivation

MOBILITY OF THE ELECTRON AND CURRENT

Mobility of electron (ue) is defined as the drift velocity of electron per unit electric field applied.

ue= drift velocity/electric field= Vd/E

Thus                                 Vd=ueE

The  SI unit of mobility is m2s-1V-1 or ms-1N-1C

As  by the relation of the current and drift velocity (already discussed)

I=Anevd (1)

By putting value of vd in above equation we get

I=AneueE

OHM’S LAW Continue reading “Ohm’s law and its derivation”

RELATION BETWEEN CURRENT AND DRIFT VELOCITY

Let l is the length of the conductor and A uniforms area of cross-section.

Therefore, the volume of the conductor = Al

If n is the number of free electrons per unit volume of the conductor, then the total number of free electrons in the conductor=A/n.

If e is the charge on each electron then total charge on all the free electrons in the conductor

Q=A/ne                                     (1) Continue reading “RELATION BETWEEN CURRENT AND DRIFT VELOCITY”

Coercivity

Coercivity is defined as the value of the magnetising field at which the intensity of magnetisation becomes zero. It is also known as coercive field.

Hence, the coercivity of a material is a measure of the strength of the reverse magnetising field required to finish out the residual magnetism of the magnetic material.

Reference: This article is referred from my authored book “electrical engineering materials” having ISBN 978-81-272-5491-9. In case of any doubt, then comment it.

Retentivity

The magnetism remaining in the magnetic material, even when the magnetising field is reduced to zero is called residual magnetism. The power of retaining this magnetism is called the retentivity or remanence.

Therefore, the retentivity is also defined as the measure of the magnetisation remaining in the material when the field is totally removed.

Reference: This article is referred from my authored book “electrical engineering materials” having ISBN 978-81-272-5491-9. In case of any doubt, then comment it.

Soft magnetic materials

Soft magnetic materials have low retentivity and low coercivity. These are those materials which have high initial permeability, low hysterisis loss and large magnetic induction. These materials can be easily magnetised and demagnetised. Therefore, these are known as soft magnetic materials.

Reference: This article is referred from my authored book “electrical engineering materials” having ISBN 978-81-272-5491-9. In case of any doubt, then comment it.

Ferrites

Ferrimagnetic materials commonly known as ferrites, can be generally represented by chemical formula XOFe2O3,

where X stands for Mn, Co, Ni, Cu, Mg, Zn, Cd etc.

If X is Fe, then compound is Fe3O4.

X-ray crystallography proves that ferrites are usually crystals and have a spine structure.

Reference: This article is referred from my book “electrical engineering materials” having ISBN 978-81-272-5069-0. In case of any doubt, comment it or post it.

Applications of ferrites

Ferrites have following applications:

  • Ferrites have importance in engineering and technology because they possess spontaneous magnetic moment below the Curie temperature just as iron, cobalt, nickel.
  • Due to vey low eddy current losses, ferrites are used as a core of coils in microwave frequency devices and computer memory core elements.
  • Due to relatively low permeability and flux density compared to iron, ferrites are not suitable for the use in high field and high power applications, such as motors, generators and power transformers, but they can be used in low field and low power applications.
  • Ferrites are used as ferromagnetic insulators in electrical circuits.
  • Ferrites like ZnO find low frequency applications in timers. They are also used as switches in refrigerators, air conditioners, etc.
  • Ferrites are used as magnetic head transducer in recording.

Reference: This article is referred from my book “electrical engineering materials” having ISBN 978-81-272-5069-0. In case of any doubt, comment it or post it.

Hard magnetic materials

Hard magnetic materials are those which have high coercivity, high retentivity and low loss in magnetisation due to mechanical treatment and no effect of temperature. These materials are called hard because these are difficult to magnetise and demagnetise. The higher the value of coercive force the harder is the magnetic material.

Example: The strength of the reverse magnetic field that is coercivity needed to completely demagnetise steel is more than that required for iron.

Reference: This article is referred from my book “electrical engineering materials” having ISBN 978-81-272-5069-0

Induced anisotropy

In case of polycrystalline solids, the various crystals in a polycrystals are randomly oriented, so that properties are same in all directions. However if specific treatment such as cold rolling is given to certain polycrystalline substances, then magnetic properties become different in different directions. This anisotropy produced in the material is called induced anisotropy.

This property is of practical importance.

Example: thin films of Ni-Fe alloy deposited on to a substrate by evaporation in vacuum with magnetic field applied in the plane of the substrate show spontaneous magnetisation in the direction of the applied field. These magnetic films are used as storage devices in computers.

Reference: This article is referred from my book “electrical engineering materials” having ISBN 978-81-272-5069-0

Magnetic Anisotropy

Magnetic anisotropy is that property due to which ferromagnets tend to magnetize along certain crystallographic axes, called directions of easy magnetization.

Example: In certain single crystals such as iron.

The magnetic properties depend upon the direction in which these are measured.

In case of iron, there are six preferred directions of spontaneous magnetisation.

In case of iron

Reference: This article is referred from my book “electrical engineering materials” having ISBN 978-81-272-5069-0