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Introduction
The term “magnetism” is derived from an island in Greece, which was then called Magnesia. The island contained deposits of magnets back in 600BC. Hans Christian Oersted made an observation that later indicated the relationship between electricity and magnetism. While performing experiments, he observed that the magnet gets deflected if kept near wires carrying current.
His work illustrated that one way to produce magnetic effects is by moving electrical charges. One of the branches of Physics that talks about magnetism due to the electric current is known as electromagnetism.
Magnetism is the force exerted by a magnet to attract or repel other objects. The substances are steel, iron, and nickel. Magnetic materials are those materials that show some magnetic properties when kept beside a magnet.
Matter and Magnetism
Magnetism occurs due to magnetic fields surrounding a matter. This leads to the formation of magnetic materials that react in a certain way.
Common properties of magnets:-
Attractive- They tend to attract iron, nickel, and steel substances.
Directive property: Materials having magnetic property align in a north-south direction.
Like magnetic poles repel and unlike ones attract each other.
Magnetic poles cannot be isolated, which signifies that they always exist in pairs.
Magnetic field lines: These are curved lines that tell the direction of a magnetic field.
Magnetic induction: A magnet tends to induce some magnetic property to a nearby substance. This process is called magnetic induction.
Magnetic dipole:- The setup of two equal and opposite magnetic poles which are separated by some distance is known as a magnetic dipole.
Magnetic dipole moment:- It is calculated as the product of its pole strength and magnetic length.
Classification of Magnetic Materials
Magnetic materials are broadly divided into the following categories based upon their property.
Property | Diamagnetic substances | Paramagnetic substances | Ferromagnetic substances | |
1. | Effect of magnets | Slowly repelled by magnets. | Weakly attracted by magnets. | Strongly magnetised. |
2. | In an external magnetic field | Achieve weak magnetisation in the opposite direction of the field. | Achieve weak magnetisation in the same direction as that of magnetising fields. | Achieve strong magnetisation in the same direction as that of magnetising fields. |
3. | In a non-uniform magnetic field | Move slowly from stronger to weaker sections in the magnetic field. | Move slowly to stronger portions from weaker ones in the same magnetic field. B | Move rapidly from weaker to stronger portions of the same magnetic field. |
4. | In a uniform magnetic field | A freely hung diamagnetic rod lines up itself perpendicular to the magnetic field. | It lines up parallel to the field. | Behaves the same as paramagnetic material. |
5. | Susceptibility value (m) | Susceptibility is small and negative. | It is positive and small. 0m | Susceptibility is positive and shows a large value. m> 100 |
6. | Relative permeability value (r) | A bit less than 1 0r<1 | A bit greater than 1 1<r<1+ | Of the order of 1 |
7. | Permeability value | < 0 | < 0 | >> 0 |
8. | Effect of temperature | The susceptibility of the material is not dependent on temperature. | Susceptibility is inverse to the temperature. m 1T | Susceptibility decreases with temperature in a complex way. m1T-TC, (T>TC) |
9. | Removal of the magnetising field | When the magnetising field is lost, the magnetization will also be lost. | When the magnetising field is lost, the magnetization will also be lost. | The magnetisation is retained after the field is lost. |
10. | Variation of M concerning H | M changes linearly with H. | M changes linearly with H. | M changes non linearly with H. |
11. | Hysteresis effect | It shows no hysteresis. | B-vector shows no hysteresis. | B-vector shows some hysteresis. |
12. | The physical state of the material | Gas, liquid, or solid | Gas, liquid, or solid. | Usually solids only. |
13. | Examples | Bi, Cu, Pb, NaCl, Si, H2O, N2(at STP) | Na, O2(at STP), CuCl2, Al, Ca | Ni, Co, Fe2O3, Alnico, Fe, Gd |
- Hysteresis: It is the process of lagging of magnetic induction before the magnetising field.
Conclusion
Till now, we discussed magnetism’s magnetic force in detail. The magnetic material has the property to point in a north-south direction. Like poles of a magnet repel and unlike poles attract each other. The Earth resembles a large magnet having magnetic properties. Magnetic materials are those which possess magnetic properties. These are of 3 types- diamagnetic, ferromagnetic, and paramagnetic. All of them acquire different properties when kept in the same magnetic field.
