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प्रश्न
Explain ferromagnetism on the basis of the domain theory.
Explain ferromagnetism with the help of suitable diagrams, using the concept of magnetic domain.
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उत्तर १
Due mostly to the electrons' spin magnetic moments, ferromagnetic material atoms have a persistent non-zero magnetic dipole moment. Little areas known as domains make up a ferromagnetic substance, according to the domain hypothesis. An incredibly small area with a high concentration of atoms—roughly 1015 atoms, or the same number as ordinary iron—is called a domain. Even in the absence of an external magnetic field, the atomic magnetic moments of nearest-neighbour atoms within each domain interact strongly through exchange interaction, a phenomenon described by quantum mechanics. As a result, the atoms align themselves parallel to one another. That is, a domain becomes spontaneously magnetised to saturation. In an unsealed substance, on the other hand, the net magnetisation is zero due to the distinct domains' magnetisation orientations being so aligned.
Domains in a single crystal of iron The arrows indicate the direction and magnitude of the magnetization of each domain.
The specimen becomes more magnetised as a result of applying an external magnetic field. One of two methods is used to do this: either a favourably oriented domain expands at the expense of a less favourably oriented domain, or the magnetisation direction of an entire domain shifts to align with the external magnetic field. Favourably oriented domains increase in size by domain border displacement when a weak magnetic field is applied, as shown in Fig. (b). Figs. (c) and (d) show how domain rotation causes the domains to shift their magnetisation under strong fields. When domains line perfectly, as they do in Fig. (d), they combine to form a single, huge domain.
It might be energetically advantageous for a domain's direction of magnetisation to continue after the external field is eliminated. A persistent magnetic dipole moment is thus present in the specimen. The existence of permanent magnets is based on a phenomenon known as magnetic remanence.
उत्तर २
Ferromagnetism based on domain theory:
- Individual atoms in ferromagnetic materials are linked to significant magnetic moments.
- The magnetic moments of atoms close to each other interact and naturally line up in the same way over large areas known as domains.
- Each domain typically measures approximately 1 mm and comprises around 1011 atoms. So, each domain possesses a significant magnetic moment.
- Without an external magnetic field, these domains are arbitrarily oriented, resulting in a net magnetic moment of zero.
- When subjected to a magnetic field, all of the domains align with one another along the direction of the field being applied.
- Magnets aggressively attract ferromagnetic materials.
- The alignment of domains may occur in either of the two ways.
- By displacing the boundaries of domains.
- By rotation of domains.
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संबंधित प्रश्न
Distinguish between ‘paramagnetic’ and ‘ferromagnetic’ substances.
Give any ‘two’ points of differences between diamagnetic and ferromagnetic substances.
The susceptibility of magnesium at 200 K is 1.8 x 10-5. At what temperature will the susceptibility decrease by 6 x 10-6?
In what way is the behaviour of a diamagnetic material different from that of a paramagnetic, when kept in an external magnetic field?
Out of the two magnetic materials, 'A' has relative permeability slightly greater than unity while 'B' has less than unity. Identify the nature of the materials 'A' and 'B'. Will their susceptibilities be positive or negative?
Distinguish between diamagnetic and paramagnetic substances.
The susceptibility of a magnetic material is 0·9853. Identify the type of magnetic material. Draw the modification of the field pattern on keeping a piece of this material in a uniform magnetic field.
The relative magnetic permeability of a magnetic material is 800. Identify the nature of magnetic material and state its two properties.
Two substances A and B have their relative permeability slightly greater and slightly less than 1 respectively. What do you conclude about A and B as far as their magnetic materials are concerned?
Identify the following magnetic materials :
Which of the following statements is correct for diamagnetic materials?
Choose the correct option:
A magnetising field of 360 Am−1 produces a magnetic flux density (B) = 0.6T in a ferromagnetic material. What is its permeability in Tm A−1?
A rod of magnetic material of cross-section 0.25 cm2 is placed in a magnetizing field of intensity 4000 A/m-1. The magnetic flux passing through the rod is 25 × 10-6 Wb. Find out
(a) relative permeability
(b) magnetic susceptibility and
(c) magnetisation of the rod.
A domain in a ferromagnetic substance is in the form of a cube of side 1 µm. If it contains 8 × 1010 atoms and each atomic dipole has a dipole moment of 9 × 10-24 Am2 then the magnetisation of the domain is ______.
The susceptibility of a magnetic material is positive and small. The material is ______.
The magnetic susceptibility of a paramagnetic material at - 73 °C is 0.0075. Its value at -173 °C will be ______.
Magnetization of the sample is ______.
Magnetic material can be easily magnetized if magnetic susceptibility is ______.
If a magnetic field is applied to a liquid in one arm of a narrow U-tube, the liquid level in that arm is lowered. The liquid in U-tube arm is ______.
The magnetic property of magnetic substance is associated with ____________.
A sphere of gold when brought towards a powerful magnet experiences ____________.
A small quantity of paramagnetic liquid is taken in a watch - glass and kept on two dissimilar magnetic poles. The liquid ____________.
A domain in a ferromagnetic substance is in the form of a cube of side length 1 µm. If it contains 6 x 1010 atoms and each atomic dipole has a dipole moment of 7 x 10-24 Am2, then magnetization of the domain is ____________.
The earth’s field departs from its dipole shape substantially at large distances (greater than about 30,000 km). What agencies may be responsible for this distortion?
A short bar magnet has a magnetic moment of 0.48 J T−1. Give the direction and magnitude of the magnetic field produced by the magnet at a distance of 10 cm from the centre of the magnet on
- the axis,
- the equatorial lines (normal bisector) of the magnet.
Why is diamagnetism, in contrast, almost independent of temperature?
Magnetic field lines are always nearly normal to the surface of a ferromagnet at every point. (This fact is analogous to the static electric field lines being normal to the surface of a conductor at every point.) Why?
Would the maximum possible magnetisation of a paramagnetic sample be of the same order of magnitude as the magnetisation of a ferromagnet?
What kind of ferromagnetic material is used for coating magnetic tapes in a cassette player, or for building ‘memory stores’ in a modern computer?
Nickel shows ferromagnetic property at room temperature. If the temperature is increased beyond curie temperature, then it will show ______.
Assertion: The ferromagnetic substance do not obey Curie’s law.
Reason: At Curie point a ferromagnetic substance start behaving as a paramagnetic substance.
The magnetic susceptibility is negative for ______.
Metals getting magnetised by orientation of atomic magnetic moments in external magnetic field are called ______.
Two identical bar magnets are fixed with their centres at a distance d apart. A stationary charge Q is placed at P in between the gap of the two magnets at a distance D from the centre O as shown in the figure. The force on the charge Q is ______.
The magnetic susceptibility for diamagnetic materials is ______.
According to the Atomic theory, on heating a magnet, the thermal energy of the elementary magnet ______
S is the surface of a lump of magnetic material.
- Lines of B are necessarily continuous across S.
- Some lines of B must be discontinuous across S.
- Lines of H are necessarily continuous across S.
- Lines of H cannot all be continuous across S.
Essential difference between electrostatic shielding by a conducting shell and magnetostatic shielding is due to ______.
- electrostatic field lines can end on charges and conductors have free charges.
- lines of B can also end but conductors cannot end them.
- lines of B cannot end on any material and perfect shielding is not possible.
- shells of high permeability materials can be used to divert lines of B from the interior region.
From molecular view point, discuss the temperature dependence of susceptibility for diamagnetism, paramagnetism and ferromagnetism.
Magnetic susceptibility for a paramagnetic and diamagnetic materials is respectively ______.
Which of the following has a permeability less than that of free space?
The relative magnetic permeability of a substance X is slightly less than unity and that of substance Y is slightly more than unity, then ______.
What is magnetic hysterisis?
Explain the origin of paramagnetism on the basis of atomic structure.
State the dimensions of magnetization.
Explain the meaning of the following statement:
Curie temperature for soft iron is 770°C.
