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来源:QQ解答    发布时间:2019年08月22日 09:34:34    编辑:admin         

This is a neodymium magnet-its pretty darn strong.And now,after heating it in a flame...its 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。Thats easy-theyre 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。However,its 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 wont 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.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,无法克其本身的震动。That is,their temperature!In which case,even though all the individual atoms in the material are magnetic,the material as a whole isnt.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:its attracted by a magnet,though it doesnt stay magnetized afterwards.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。But lets 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 wont 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.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。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.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。201507/384597。

;Thanks a lot;这么客气的话为什么会引起美国人的误会?问题出在哪儿?英语表达感谢应该怎么说呢?今天Jenny,Jason就要告诉你。201507/384445。

Coal, steam, and a new sensation, speed.煤 蒸汽 还有一种全新的感觉 速度We have always strived to go further, faster.我们总是努力走得更远 更快5,000 years ago,The horse triples the distance we can cover in a day.五千年前 马儿将我们日行的距离增加了两倍By train, we travel ten times farther.而有了火车 我们行进速度快了十倍Imagine your first trip on a steam railroad.想象一下你乘坐蒸汽火车的首次旅行You climb into this carriage behind this belching, vast, smoking machine,你爬进车厢内 前面是呼啸着喷涌烟雾的巨大机器traveling so fast, they thought your lungs might explode or your eyes might pop out.行驶速度快得惊人 让人感觉肺要炸开 眼球要蹦出来了The idea of traveling 20 miles an hour,it was mind-boggling.那时二十英里的时速 就让人觉得难以置信They would comment on how fast they were traveling,人们不停议论着极速的旅程and they werent at all sure the human body could sustain this.他们从不知道人类能够承受 这样的速度极限The Baltimore-Ohio railroad is Americas most ambitious tunneling project.巴尔的到俄亥俄的铁路 是美国最伟大的隧道工程The man in charge: Benjamin Latrobe, Jr.总工程师是小本杰明·拉特罗布The son of an architect,Hes become one of the leading engineers in the US.他是位建筑师的儿子 当时的他已是美国一流的工程师了The obstacle he faces: the Appalachian Mountains.他所面临的最大困难就是阿巴拉契亚山脉A towering wall of slate and limestone,这面由页岩和石灰石构成的高耸墙壁between the east coast and the rest of the continent.将东海岸与大陆隔绝开来201604/436214。

栏目简介:;Shanghai Live; focuses on big events in the city and major issues around the world, and presents them in a practical and audience-friendly manner to meet the ever-evolving needs of Shanghais English-speaking viewers,both local and expatriate.《直播上海英语电台》集中报道城市大事件以及全球热点话题,并以观众喜闻乐见的方式呈现给大家,从而满足上海本地以及上海海外人士的英语需求。201509/396667。

He decides he will lead the Jews out of exile他决定带领被流放的犹太人And back to the promised land.重回应许之地But many dont want to go,但很多犹太人并不愿回去They have lived their entire lives in Babylon,他们一生都居住在巴比伦And the journey will be dangerous.而且他们相信回去的路必定危机重重Zerubbabel persuades a hundred families to leave.所罗巴伯说了一百户人家和他同行Their departure from Babylon will become a new chapter他们离开巴比伦后将开启人类历史上In the story of mankind:一个新的篇章;Go out from Babylon, flee from the Babylonians.;离开巴比伦 逃离巴比伦人的统治;Declare this with a shout of joy,;仰天长啸 告诉整个世界;Proclaim it, send it out to the end of the earth:;向他们宣告 让这声音传遍世界的每个角落;Say, The Lord has redeemed his servant.;;我们要说 上帝拯救了祂的仆人们An epic journey of 500 miles长达五百公里史诗般的旅程Back to the sacred city they have never seen:只为回到那片他们从未见过的圣地:Jerusalem.耶路撒冷201510/401683。



He wasnt always patient.他不是次次都很有耐性He wasnt always saying things that you wanna hear,也不会总是说好听的话or saying it right.或是很得体的话But what he said and what he was doing was just trying to make them stars.但他的所作所为 都是为了要造就巨星Our last day at the Regal Theater我们在理格剧院的最后一天is when l went to Joe, l said,我跟乔说say now, why dont you let me put these kids at Motown? 不如你让我把这群孩子们 签到城吧And Joe said those words to me, Man, l thought youd never ask. 乔这么回答我 老兄 我等的就是你这句话We were in New York City.我们当时在纽约And we had just finished performing with James Brown.才刚结束与詹姆斯·布郎的演出We were opening up for him.我们帮他开场Bobby Taylor had been begging Berry to check us out.鲍比·泰勒一直恳求贝瑞来观赏And he wouldnt do it because he had another kid on his label.他一直不愿意 因为他旗下还有另一名歌手And he was catching a lot of flak from the state州政府一直找他麻烦about working this kid whos underage.因为这孩子还未成年Berry would say, l never wanna have anything to do with kids in this business.贝瑞说 我在这行 再也不想跟儿童扯上边lts too much problems.太麻烦了l cant even handle one. What am l gonna do with five? 我连一个都搞不定了 更何况是五个And the one kid was little stevie Wonder.那个孩子就是史提夫·旺达201508/394501。