Amongst the oldest and easiest to observe scientific phenomena are those of magnetism. The subject of bar mangnets and magnetic poles is given the name of magnetostatics by analogy with electrostatics. Magnetic phenomena, such as poles and the fields they produce, can be explained in terms of fields due to electrics currents. Thinking on the atomic scale, the electrons which circulate round the heavy central positive nucleus constitute a current .so each orbiting electron produces a magnetic field .in general, the orbits of electrons are disposed in random planes in space and so the net magnetic field is zero.

Should a suitable stimulus be applied, the orbits can be aligned so that their magnetic fields are in the same direction. In some materials the orbits, once aligned, stay that way and these are the materials which produce permanent magnets. In other materials the orbits return to their random dispositions once the stimulus is removed-these are the materials used as electromagnets. For a given stimulus, they produce a greater field than the materials used for permanent magnets. It should be mentioned at this stage that ability to produce a high field is not the only factor to be considered when deciding upon a material to be used for an electromagnet; there are problems of energy loss to be considered if the state of magnetization is to be changed frequently.

 

 

 

نوشته شده در تاریخ یکشنبه 1 اردیبهشت 1392    | توسط: . .    | طبقه بندی: علم و دانش، type، مطالب زبان اصلی،     |
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