urgent!! science- magnetic field

依磁分子學說，在磁鐵中磁分子排整齊時，它便具有磁性。所以想將磁鐵的磁性消失方法有下列幾種。

1)若磁鐵可以加熱，當它加熱至高溫時，它內部的磁分子便會產生劇烈的振動，這樣磁分子便會變得凌亂而失至磁性。這種方法可以使磁鐵完全失去磁性。

2)用物體大力敲打磁鐵，這種方法亦可以使磁鐵的磁分子振動，但效果會比加熱為差，亦會因地球的磁場，而使它殘留磁性。

3)用一個線圈，通以強的變化電流，在強電流下，磁鐵內的磁分子亦會因外界的磁場因而產生振動，這時將外界電流漸漸減少，便可以將磁鐵消磁，這種方法是最常用，而亦不會影響磁鐵的本質。

不單鐵可以帶磁性，而鈷、鎳等都可以磁化，而強磁鐵是用鐵的合金製成。

鐵鈷鎳等材料可稱為磁性材料，若用磁分子可說，可以說這些物質內有磁分子的存在。當外界有強磁場時，它的磁分子便可以順著磁場排列，變成磁鐵。

所以想將鐵磁化，可以用強磁鐵使它磁化，亦可利用線圈，通過強電流產生強磁場，使鐵磁化。

但有些材料，當磁分子排列整齊後便可以變成磁鐵，但外界磁場消失後，它的磁分子便變回不規則，它便會失去磁性，這種便是暫時磁鐵，它可以加強電磁鐵的磁性。但有些則可以保持磁分子的排列，而可變成永久磁鐵。

在物理書上說，鐵不可以磁化，鋼可以磁化。其實只不過是一種粗略的說法，鐵有很多種，而鋼亦是鐵的一鐵。所以不是所有鐵都不可以磁化為磁鐵的。

Magnets attract because of the existence of a magnetic field. A magnetic field contains energy, whenever a substance is placed into a magnetic field, the objects will try to align themselves so that the energy stored in the field will be reduced to a minimum. If a mangetic dipole (e.g. a magnet) is placed in the magnetic field of another magnet, they try to align in opposed polarity, because in this configuration the energy in the magnetic field is minimum. (An analogy to this is the gravitational force field. A book is subject to the gravitational force field of earth, the book therefore tries to fall to the earth's center, because in that configuration, energy in the gravitation force field is minimum)

All charged particles are subjected and affected by a magnetic field. Because all atoms contain charged particles (electrons, protons), they are all subjected to the effects of a magnetic field. Whenever a substance is placed inside a magnetic field, the orbital motions of the electrons change. The result is known as "diamagnetism". For most materials, diamagnetismis the only effect. The effects of diamagnetism is usually too small to be observed, and so substances which only have diamagnetic effects are called "non-magnetic". Water, DNA, e.g. are examples.

Certain atoms exist another effect under magnetic field, known as paramanetism. Susbtances that exhibits paramagnetism are attracted by the magnetic field. Paramagnetism is stronger than diamagnetism but yet much weaker than the next kind of magnetic state, ferromagnetism.

Ferromagnetism is what we usually observed daily from things such as magnets or irons. Permanent magnets or "temporary" magnets all exists ferromagnetism. Ferromagnetism exists on certain kinds of materials in crystalline form, when they are below a particular temperature (known as Cuire point). The most common one is iron, which has a curie point of 1043K. Above the curie point, ferromagnetism will disappear.

Whether a substance will exhibit ferromagnetism or paramagnetism or just diamagnetism depends on the orbits and orders of the electrons in its atoms.

OTOH, magnetic field, according to Eistein's Relativity, is in fact part of the electro-magnetic field.

2007-01-04 02:13:17 補充：
BTW, there's no such thing as 磁份子　in this world.

2007-01-04 02:33:17 補充：
BBTW, if it's school science subject question... go ask your teacher what's the relationship between magnetism and electric field. If he/she doesn't mention "relativity" or "Albert Eistein", you know he/she actually knows nothing about the subject!