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英语煎蛋小学堂视频百科115:如何让磁铁“消磁(MP3+中英双语)

cocotang 于2015-07-01发布 l 已有人浏览
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英语视频:煎蛋小学堂115:如何让磁铁“消磁,以幽默诙谐的方式为你解答那些那些你意想不到的科学小知识,含有中英双语字幕视频,mp3下载。
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This is a neodymium magnet-it's pretty darn strong.And now,after heating it in a flame...it's no longer magnetic.Well,to build a magnet,all you need to do is find a bunch of magnetic atoms .

这是一上钕磁铁,它磁性很强,现在在火焰炙烤后它没有磁性了,怎么了 想要做磁铁,你先得找到一些磁性的原子。

That's easy-they're the ones with half-filled electron shells in the middle of any of the major blocks of the periodic table,and then make a compound where the magnetic fields of the atoms align in the same direciton this is Ferromagnetism,named after Iron,which is pretty darn magnetic.

这简单 它们就是那些外层电子半满的原子,在元素周期表中主块中间的位置 然后合成原子的磁场方向都相同的化合物,这是磁铁,以铁命名,磁性较强 但是事情没这么简单。
 
有时原子的磁场方向肢相互交替 这种被称为“抗铁磁性”这就意味着这块村料不产生磁场 或者 有时原子磁场相互对挤(或交替对挤)的趋势太弱 无法克服其本身的震动。

However,it's not always so easy.Sometimes the atoms actually want to align their magnetic fields in alternating directions.This is called "anti-ferromagnetism,"and it means the bulk material won't have a magnetic field at all.Or,sometimes the tendency of the atomic magnets to align (or anti-align)is just too weak to overcome their intrinsic jiggling.

也就是温度此时即使村料内部所有原子都具有磁性 整块材料却没有 但是 在外部强磁场内 原子会沿平行于外部场的方向相互对齐,这就是顺磁性 液氧就是个好例子 它会被磁铁吸引 但之后并不会保持磁性。

That is,their temperature!In which case,even though all the individual atoms in the material are magnetic,the material as a whole isn't.However,in a strong external magnetic field,the atoms do tend to align with each other in the direction parallel to the field.This is called "para-magnetism,"and liquid oxygen is a great example:it's attracted by a magnet,though it doesn't stay magnetized afterwards.

那么回到开始的问题 怎么去持物体的磁性 材料仅能在温度足够低时表现出磁性 超过某一点是 整齐排布的原子磁场会“熔”成一片混乱 正如冰在加热至零摄氏度以上会化成水 想要去掉磁铁磁性 你得将物体加热 超过其“磁性转变点”又称“居里点”看上去似乎什么也没发生 但当原子振动足够剧烈时 它们磁场将不再都指向相同的方向。

But let's get back to the question-how do you destroy a magnet?Well,a material can only be ferromagnetic it its temperature is low enough:above a certain point,the nicely ordered atomic magnetic fields"melt"into disorder,just as ice crystals melt into water when heated past zero celsius. So to destroy a manget,you just need to heat it up past its "magnetic melting point",called the "Curie Temperature"it probably won't look like much is happening,but once the atoms are jiggling around enough,their magnetic fields will no longer all point in the same direction.

没有磁性啦 正如不同的材料熔点不同 它们的磁性转变点的温度也不同 你可以在这个动态元素周期表中试试看 那里还有所有元素周期表视频。

Magnet destroyed!And just as different elements melt from solid to liquid at different temperatures,They also melt from being ferromagnetic to paramagnetic at different temperatures,which you can explore in this sweet interactive periodic table.Which also plays all of the Periodic Table of Videos.

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