Theory of EMF Presentation By Abdul Latif Abro

Theory of EMF Presentation By: Abdul Latif Abro (K 12 EL 05)

Types of Materials Contents: Introduction to Magnetic Materials Types of Magnetic Materials Classification of Magnetic Materials • Diamagnetic Materials • Paramagnetic Materials • Ferromagnetic Materials

Introduction n. These are the materials which exhibit the magnetic material in them such materials are called as magnetic materials. n. Materials respond differently to the force of a magnetic field. n. There are three main classifications of magnetic materials. n. A magnet will strongly attract ferromagnetic materials, weakly attract paramagnetic materials and weakly repel diamagnetic materials.

Introduction n The orientation of the spin of the electrons in an atom, the orientation of the atoms in a molecule or alloy, and the ability of domains of atoms or molecules to line up are the factors that determine how a material responds to a magnetic field. Magnetic materials doesn’t mean that they will only have magnetic property in the magnetic field. These material have property to magnetization which they retain even in absence of applied field.

Types of Magnetic Material

Types of Magnetic Material n There are two types of Magnetic Material A. Soft Magnetic Material Hard Magnetic Material B.

Types of Magnetic Material n n n Soft magnetic materials can easily be demagnetized or magnetized unlike hard magnetic material which they retain their magnetizing property even when field is removed. Soft magnetic materials have less hysterias loss and eddy current loss compare to hard magnetic materials. Hard Magnetic Materials have low Susceptibility and permeability while soft magnetic materials have both parameters high.

Classification of Magnetic Material

Atomic dipole configuration with and without an external magnetic field for a paramagnetic material.

Magnetic Material are classified into three categories: 1. Diamagnetism 2. Para-magnetism 3. Ferromagnetism. n All materials exhibit at least one of these types, and the behavior depends on the response of electron and atomic magnetic dipoles to the application of an externally applied magnetic field.

Ferromagnetism n n n Ferromagnetic materials are strongly attracted by a magnetic force. The elements iron (Fe), nickel (Ni), cobalt (Co) are such materials. Magnetic susceptibilities is high for ferromagnetic materials. The reasons these metals are strongly attracted are because their individual atoms have a slightly higher degree of magnetism due to their configuration of electrons, their atoms readily line up in the same magnetic direction and the magnetic domains or groups of atoms line up more readily.

n Furthermore, in a ferromagnetic material, coupling interactions cause net spin magnetic moments of adjacent atoms to align with one another, even in the absence of an external field. n Figure shows representation of domains: Mutual alignment of atomic dipoles for a ferromagnetic material in absence of external field

Diamagnetism n When an external magnetic field is applied to a material, these always tend to align in such a way as to oppose the applied field In a diamagnetic material the atoms have no net magnetic moment when there is no applied field. n When Diamagnetic Materials are placed in the external magnetic field the magnetic lines does not prefer to pass through them. n Bismuth and carbon graphite are the strongest diamagnetic materials.

n The magnitude of the induced magnetic moment is extremely small, and in a direction opposite n n n to that of the applied magnetic field. Diamagnetic materials have a very weak negative susceptibility, typically of order − 10− 6 Thus, the relative permeability is less than unity. Consequently, when a diamagnetic material is placed in a magnetic field, B < µ 0 H.

n Figure shows the atomic dipole configuration for a diamagnetic material with and without a magnetic field. (a) (b) (a) In the absence of an external field, no dipoles exist; (b) In the presence of a field, dipoles are induced that are aligned opposite to the field direction.

Paramagnetism n These are magnetic material the dipole moment of the individual atom is not equal to zero but the net dipole moment of material is zero This is because the different dipole are randomly oriented hence therefore vector sum is equal to zero. n n In the absence of an external magnetic field, the orientations of these atomic magnetic moments are random, such that a piece of material possesses no magnetization. These atomic dipoles are free to rotate, and Para magnetism results when they preferentially align, by rotation, with an external field.

n n In such materials dipoles align with the external field, they enhance it, giving rise to a relative permeability that is greater than unity, and to a relatively small but positive magnetic susceptibility. Paramagnetic substances always moves from a region of weaker magnetic field to region of stronger magnetic field. n n Susceptibilities for paramagnetic materials range from about to 10 -5 or 10 -2. Paramagnetic Substances have value of susceptibility So, that’s why magnetic lines of force are prefer to pass through them. n NOTE: Both diamagnetic and paramagnetic materials are considered to be nonmagnetic because they exhibit magnetization only when in the presence of an external field.