Magnets Essay, Research Paper

Diamagnetics was discovered by Michael Faraday in 1846, but no 1 at the clip thought that it could take to any appreciable effects. William Thomson ( Lord Kelvin ) , mentioning to levitation as the job of “ Mohamet? s casket, ” had this to state: “ It will

obably be impossible of all time to detect this phenomenon, on history of the trouble of acquiring a magnet strong plenty, and a diamagnetic substance sufficiently light, as the [ magnetic ] forces are overly lame. ”

William claude dukenfields strong plenty to raise diamagnetic stuffs became available during the mid-20th century. In 1939, Werner Braunbeck levitated little beads of black lead in a perpendicular electromagnet. Graphite has the largest ratio degree Celsius /r known for diamagnetics ( 8 & # 215 ; 10-5

m3/g ) ; today, this experiment can be repeated utilizing merely a strong lasting magnet, such as one made of Nd, Fe and B. Leaving aside superconductors ( which are ideal diamagnetics ) , foremost levitated by Arkadiev in 1947, it took another 50 Y

R to rediscover the possible levitation of conventional, room-temperature stuffs. In 1991, Eric Beaugnon and Robert Tournier magnetically lifted H2O and a figure of organic substances. They were shortly followed by others, who levitated liquid hydrog

and He and toad eggs. At the same clip, Jan Kees Maan rediscovered diamagnetic levitation at the University of Nijmegen, in coaction with Humberto Carmona and Peter Main of Nottingham University in England. In their experiments, they levitated

ractically everything at manus, from pieces of cheese and pizza to life animals including toads and a mouse. Unusually, the magnetic Fieldss employed in these experiments had already been available already for several decennaries and, at possibly half a vitamin D

en research labs in the universe, it would hold taken merely an hr of work to implement room-temperature levitation. Nevertheless, even physicists who used strong magnetic Fieldss every twenty-four hours in their research did non acknowledge the possibility.

If you were to state to a kid playing with a horseshoe magnet and pieces of Fe that his uncle has a much bigger magnet that can raise everything and everybody, the kid would likely believe you and might even inquire for a drive on the magnet. If a phy

cist were to state such a thing, he or she ( armed with cognition and experience ) would likely smile patronizingly. The physicist would cognize that merely a really few stuffs, such as Fe or Ni, are strongly magnetic. The remainder of the universe? s stuff

are non ; or to be precise, the remainder of the universe is a billion ( 109 ) times less magnetic. This figure seems excessively large to let common substances ( H2O, for illustration ) to be lifted even by the most powerful magnets. A billionfold addition in magnetic Fieldss

an be found merely on neutron stars. In this instance, nevertheless, cognition and experience would misdirect the physicist: In fact, all stuffs can be lifted by utilizing magnetic Fieldss that are instead standard these yearss.

Whether an object will or will non levitate in a magnetic field B is defined by the balance between the magnetic force F = MB and gravitation mg = V g is the material denseness, V is the volume and g = 9.8m/s2. The magnetic minute M = ( / & # 181 ; 0 ) VB so that F = ( /

& # 181 ; 0 ) BVB = ( /2 & # 181 ; 0 ) VB2. Therefore, the perpendicular field gradient B2 required for levitation has to be larger than 2 & # 181 ; 0 g/ . Molecular susceptiblenesss are typically 10-5 for diamagnetics and 10-3 for paramagnetic stuffs and, since is most frequently a few g/

cm3, their magnetic levitation requires field gradients ~1000 and 10 T2/m, severally. Taking fifty = 10cm as a typical size of high-field magnets and B2 ~ B2/l as an estimation of the order of 1 and 10T are sufficient to do levitation of para- and diama

netics. This consequence should non come as a surprise because magnetic Fieldss of less than 0.1T can levitate a superconductor ( = -1 ) and, from the expressions above, the magnetic force additions as B2.

By the way, this is the most general rule of Nature: whenever one tries to alter something settled and quiet, the reaction is ever negative ( you can easy look into out that this rule besides applies to the interac

on between you and your siblings ) . So, harmonizing to this rule, the disturbed negatrons create their ain magnetic field and as a consequence the atoms behave as small magnetic acerate leafs indicating in the way antonym to the applied field.

All the atoms inside the toad, act as really little magnets making a field of approximately 2 Gauss ( although really little, such a field can still be detected by a compass ) . One may state that the toad is now built up of these bantam magnets all of which are repelled

y the big magnet. The force, which is directed upwards, appears to be strong plenty to counterbalance the force of gravitation ( directed downwards ) that besides acts on every individual atom of the toad. So, the toad? s atoms do non experience any force at all and the toad

loats as if it were in a ballistic capsule.

* ) There are a few stuffs ( such as Fe ) whose atoms are a spot brainsick and love to be in a magnetic field. Their magnetic? acerate leafs? are oriented in the same way. But those are exclusions from the general regulation.

A hazeln

Greenwich Mean Time, a toad, and a globule of H2O all hovering, or levitating, have to be in a in a magnetic field of at least 10 T. This field strength is merely several times more than that of bing lasting magnets ( about 1.5 T ) and merely 100 times or so

ronger than that of a typical icebox magnet. One demand merely open a text edition on magnetic attraction to recognize that such Fieldss can raise “ nonmagnetic ” stuffs. Indeed, the magnetic force moving on a stuff of volume V with susceptibleness degree Celsius in a magnetic degree Fahrenheit

ld B is F = ( M & # 209 ; ) B where the magnetic minute M = ( hundred /m 0 ) VB. This force should counterbalance the gravitative force milligram = R Vg ( R is the material denseness and g is the gravitative acceleration ) and, therefore, the perpendicular field gradient & # 209 ; B2 required for lift

g has to be greater than 2m 0g ( r /c ) ( here we use “ raising ” to separate it from “ levitation ” , which means stable drifting ) .

Merely because an object can levitate does non intend that it will when placed in a strong plenty magnetic field. The right conditions are surprisingly elusive ; for case, even an addition of merely a few per centum in magnetic field will usually destabilise

evitation and do the object to fall. A diamagnetic object can levitate merely near to an inflexion point of the perpendicular constituent of the magnetic field, where d2BZ/dz2 = 0. Note that this is a strictly geometrical status, which does non depend on T

field strength. The spacial extent of the part of stable levitation is typically a little fraction of the magnet? s size & # 8211 ; merely 2 centimetres for a half-meter Bitter magnet, for illustration. Consequently, the field strength must be carefully adjusted to com

nsate for gravitation at that peculiar point. If the field is somewhat weaker than required, the object falls ; if stronger, the field is horizontally unstable and merely the magnet walls stop the object from traveling sideways and so falling.

A soft touch or airflow can easy destruct the levitation. Those who have tried to levitate high-temperature superconductors would likely raise their superciliums, since they encounter no jobs. However, super-conducting levitation takes advantage O

magnetic flux lines being pinned inside a superconductor ; this is what makes drifting superconductors such a familiar sight. Eliminate pinning, and one time once more careful accommodations of both spacial place and field strength are required.

The thought of diamagnetic levitation is so attractive that, when foremost larning about it, experimental physicists of course start believing & # 8211 ; if merely for a brief minute & # 8211 ; about using the consequence in their peculiar research. Indeed, super-conducting mom

ets with a room-temperature dullard are comparatively inexpensive these yearss, -a sensible, basic apparatus costs about $ 100,000 & # 8211 ; doing entree to the levitation low-cost even for single research groups.

Watching a levitating H2O bead in a magnet, one inevitably starts believing about analyzing weightless fluid kineticss, non on board a infinite bird but merely in a research lab. Containerless crystal growing, besides a frequent topic of infinite research, is

other obvious application to see. Or take, for illustration, diamagnetically suspended gyroscopes. In our ain recent experiment, we could detect Earth? s rotary motion utilizing a little plastic ball levitated in a magnet and spun by a optical maser beam. Not a great ach

vement in itself, but already those first effort has shown error impetuss of merely 0.1 % of Earth? s rotary motion, a record depression for any type of gyroscope.

Magnetic micro-gravity seems to work good even for complex biological systems. Several groups of biophysicists, & # 8211 ; such as those led by James Valles of Brown University, Karl Hasenstein of the University of Southwestern Louisiana and Markus Braun of the

niversity of Bonn ( Germany ) & # 8211 ; , have already begun surveies of works and animate being responses to such magnetically simulated micro-gravity. Biological systems are amazingly homogenous with regard to diamagnetic levitation: Apparently diverse constituents

ch as H2O, tissues, castanetss and blood differ in their values of degree Celsiuss /r by merely several per centum, which implies that gravitation is compensated to better than 0.1g throughout a complex life being. Further, even if paramagnetic molecules and ions are presen

as in blood, they contribute merely to the mean susceptibleness ; their strong response to the field is smeared out by temperature ( mBB & lt ; & lt ; karat ) , Brownian gesture and a much stronger matching to the environing diamagnetic molecules. Probably, the alignmen

of really long biomolecules along the field way is the magnetic consequence most likely to befog true micro-gravity in complex systems. Fortunately, one can ever look into for this and other non-microgravity effects by puting a system in an indistinguishable, B

horizontal, field gradient or in a homogenous field of the same strength.

Mentions

? Everyone? s Magnetism? by A.Geim, Physics Today, Sep.1998, page 36-39

? Of Flying Frogs and Levitrons? by M.V.Berry and A.K.Geim, European Journal of Physics, v. 18, p. 307-313 ( 1997 ) .

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