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磁悬浮

Magnetic Levitation

磁场可由电流通过电线产生
Magnets can be created by running currents through wires,
或者通过合适材料来产生
by finding a suitable material
即组成材料的原子已在磁场作用下排列好
that naturally has all the magnetic fields of its atoms aligned,
或者通过变化磁场来排列原子来产生
or by forcing the magnetic fields of atoms to align.
但仍有一种属性适用于所有物质
But there’s one more kind of magnetism that all materials exhibit,
且与组成物质的原子的磁性无关
even those whose constituent atoms aren’t magnetic——
这种磁场很弱 通常被其它更强的磁场淹没
though it’s so weak that the other kinds of magnetism often overwhelm it.
总之 外部磁场导致原子内电子排列发生变化
Basically, an external magnetic field causes the electrons around atoms in a material to
然后电子运动轨迹改变
change course,
这些电子的新的运动又产生另一个相斥的磁场
and their new motion generates an opposing magnetic field.
这种磁场很弱
This field is pretty weak,
但是却能使物质在原先磁场中受到排斥
but it does cause the material to be repulsed from the magnetic a little bit,
例如 如果把一根木牙签放到一个磁场中
for example, if you hang a wooden toothpick in a magnetic field, the
牙签本身会产生与原磁场相斥的另一个磁场 并最终与原磁场垂直
ends will repel the field and it will end up aligning across the magnetic field.
这是理解这种磁性——“逆磁性”的一种便利方法
This is a convenient way to remember the name of this kind of magnetism – diamagnetism –
“逆”意为反向穿过 就像直径是穿过圆心的
since “dia” means across, like the “diameter” measured across a circle.
逆磁性物质排斥磁级
Diamagnetic materials will repel a magnet,
“逆磁性罗盘”的指向是垂直磁场的
and a diamagnetic “compass” will point across the magnetic field –
也就是东西指向
that is, it will orient east-west.
尽管逆磁场很弱 但却很重要
As weak as it is, diamagnetism is pretty darn awesome
由于它的反斥作用:
because it’s a repulsive effect:
任何逆磁性物质都会在足够强的磁场中悬浮起来
any diamagnetic material will levitate in a strong enough magnetic field,
像这个石墨烯块 或是这个青蛙(水具有逆磁性)
Like this chunk of graphene, or, since water is diamagnetic, this frog.
原则上 人也可以通过这种方式漂浮起来
In principle, humans could also be levitated this way,
当然需要的磁场要很强
though the magnetic fields required would be enormous.
我们一笔带过了很多细微末节
There are also a lot of subtleties we’ve skated over,
比如氮原子是逆磁性的 尽管它有未配对电子
like the fact that nitrogen is diamagnetic even though as an atom it has unpaired electrons –
或许有人认为它至少是顺磁性的
one might think that it should be at the very least paramagnetic.
但是氮原子形成氮气的过程中
But nitrogen atoms bond to form N2 molecules
外部有完整的电子层
which have full outer electron shells and
因此是逆磁性物质
are thus only diamagnetic.
另一方面 我们见过的氧气分子
On the other hand, molecular O2, as we’ve seen,
也有未配对电子 但是却是顺磁性的
still has unpaired electrons, and it’s paramagnetic.
或许你也曾见过超导体是怎样在磁场中悬浮的
You’ve probably also seen how superconductors can levitate in a magnetic field,
这其实也是种完美的逆磁性现象
which is a kind of perfect diamagnetism –
通过超导体的电流不仅产生反斥磁场
not only do the currents in a superconductor create opposing magnetic fields,
也完全反斥物质本身产生的磁场
they expel magnetic fields from the material entirely.
但两者的根本原因大不相同
But the root cause is very very different,
这是我们下次要讨论的问题
and that’s a journey for another day.

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视频概述

磁悬浮和磁场形成的奥妙是什么?

听录译者

收集自网络

翻译译者

海参崴

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审核团审核员XD

视频来源

https://www.youtube.com/watch?v=BqKeiiezqzc

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