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Author Topic: lightest vs strongest magnet  (Read 12009 times)

Offline ukmicky

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lightest vs strongest magnet
« on: 12/08/2007 00:33:46 »
Are all magnets made out of heavy materials and if so are the heaviest types the most powerful.

I was just wondering as i was reading an article about levitating living things like frogs humans etc thought the use of very strong magnetic fields and was wondered if the strength of a magnet had anything to do with how dense and heavy the material it was made out of was..


 

Offline ukmicky

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Re: lightest vs strongest magnet
« Reply #1 on: 12/08/2007 00:33:49 »
Are all electro magnets made out of heavy materials and if so are the heaviest types the most powerful.

I was just wondering as i was reading an article about levitating living things like frogs humans etc thought the use of very strong magnetic fields and was wondered if the strength of a magnet had anything to do with how dense and heavy the material it was made out of was..
 

another_someone

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lightest vs strongest magnet
« Reply #2 on: 12/08/2007 02:24:01 »
The kind of magnets that cause those kind of fields, as far as I am aware, are electromagnets using superconductors.
 

Offline neilep

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lightest vs strongest magnet
« Reply #3 on: 12/08/2007 04:07:57 »
If there really was a magnet that could levitate a person would it not screw up the person too ?
 

Offline ukmicky

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lightest vs strongest magnet
« Reply #4 on: 12/08/2007 04:18:14 »
Quote
If there really was a magnet that could levitate a person would it not screw up the person too ?
Na they said they tried it on a fish and then on a Frog and i'm sure the Frog would have told them if he felt any different. ;D





PS IF YOU CAN READ THIS YOUR TO CLOSE TO YOUR MONITOR
« Last Edit: 12/08/2007 04:25:43 by ukmicky »
 

Offline neilep

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lightest vs strongest magnet
« Reply #5 on: 12/08/2007 04:32:19 »
I'm too close to the monitor !!.....
 

Offline DoctorBeaver

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Re: lightest vs strongest magnet
« Reply #6 on: 12/08/2007 07:07:15 »
Hi Micky.

As you know, my knowledge of physics is very limited so I could be (and probably am) way off the mark; but I dare say 1 of our resident physics whizzos will put us straight.

The electromagnetic force is mediated by photons and I would have thought that a heavier, denser material would be able to produce more of them due to having more constituent particles.

Then again, I don't know whether fewer but more energetic photons would be the same as more but less energetic photons.

« Last Edit: 12/08/2007 07:11:20 by DoctorBeaver »
 

Offline that mad man

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lightest vs strongest magnet
« Reply #7 on: 12/08/2007 13:20:27 »
I have just recovered 2 rare earth magnets from a dead hard drive (hope you are reading neil) and boy, are they powerful. Even for their size the magnetic field will penetrate a few inches through wood.

Slim things, a few mm thick and in an arc shape about 40mm long. They are not very heavy but they are fragile as I have broken one already.

TBH I don't know what "rare earth" means or how they are made but they must be 10 x more powerful that normal magnets.

@ neil MRI scans use a very powerful magnetic force. They have a new device just installed in Sheffield that has to be enclosed in a very thick screened room. It is so powerful that if not screened it can effect the magnetism in the area over a few miles radius.

bee
 

Offline neilep

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lightest vs strongest magnet
« Reply #8 on: 12/08/2007 14:10:37 »
Wow Bee !!..that is one powerful magnet !!...I suppose it has to be screened with lead eh ?...I say that because lead seems to be what is used to screen most things !....though  I'm probably wrong....

Could they not use magnetism to also retain the magnetism ?
 

Offline Bored chemist

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lightest vs strongest magnet
« Reply #9 on: 12/08/2007 14:24:55 »
They don't use lead- it simply wouldn't work.
The cheapest stuff to use is steel so I guess they use that.
When they are making magnetically screened rooms designed to have very little magnetic field in them they use a big thick steel shield then a layer of an alloy called mu metal which has a very high magnetic permeability which effectively "short circuits" the field.
Another trick is to use a set of coils to produce a field that opposes the external field.
The "rare earths" is a rather old name for the lanthanide elements.
http://en.wikipedia.org/wiki/Rare_earth_element
 Apart from one of them (promethium) which is radioactive and decays away, they are not that rare. Only 2 of them get used much in magnets Samarium alloyed with cobalt and neodymium alloyed with iron and boron both make really impressive permanent magnets.
 

Offline Soul Surfer

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lightest vs strongest magnet
« Reply #10 on: 13/08/2007 22:56:40 »
MRI machines also have to be screened from other magnetic fields because MRI imaging depends on setting up very precise and controllable quite large magnetic field gradients to allow the resonance frequencies to be separated out in the image.
 

Offline dentstudent

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lightest vs strongest magnet
« Reply #11 on: 14/08/2007 09:27:02 »
Quote
If there really was a magnet that could levitate a person would it not screw up the person too ?
Na they said they tried it on a fish and then on a Frog and i'm sure the Frog would have told them if he felt any different. ;D





PS IF YOU CAN READ THIS YOUR TO CLOSE TO YOUR MONITOR

and also aware of pedant spelling. s/b You're ;).
 

Offline Pumblechook

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lightest vs strongest magnet
« Reply #12 on: 09/12/2007 00:01:16 »
The magnets they used to use on the necks of CRTs were very powerful and made of a 'ferrite' material which is light and brittle.   Similar material as used on AM portable radios....ferrite rod aerial.   
 

lyner

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lightest vs strongest magnet
« Reply #13 on: 09/12/2007 18:48:40 »
Quote
The magnets they used to use on the necks of CRTs were very powerful and made of a 'ferrite' material which is light and brittle.   Similar material as used on AM portable radios....ferrite rod aerial.
They are not permanent magnets. They are ferrite 'cores' with a high permeability to 'enhance' the magnetic field around a coil carrying an electric current and have to operate at fairly high frequencies - for which iron  is too lossy.
 

Offline Bored chemist

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« Reply #14 on: 09/12/2007 20:06:09 »
The ferrites are about two thirds as dense as steel- not very light.
 

Offline techmind

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lightest vs strongest magnet
« Reply #15 on: 09/12/2007 20:27:58 »
...Apart from one of them (promethium) which is radioactive and decays away, they are not that rare. Only 2 of them get used much in magnets Samarium alloyed with cobalt and neodymium alloyed with iron and boron both make really impressive permanent magnets.

At university we used (what I think was) a neodymium-iron-boron magnet in a superconductor/levitation experiment. The little magnet was only about 3mm cube, but could easily lift an old-fashioned and fairly heavy pair of office scissors (none of the plastic-handles you get today)...
 

Offline Pumblechook

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lightest vs strongest magnet
« Reply #16 on: 09/12/2007 20:28:27 »
The magnets which used to be on the neck of old TVs where ferrite permanent magnets and much lighter than steel.
 

Offline Bored chemist

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lightest vs strongest magnet
« Reply #17 on: 09/12/2007 20:32:17 »
Since ferrites are not a lot lighter than steel...
 

Offline Pumblechook

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lightest vs strongest magnet
« Reply #18 on: 09/12/2007 20:40:08 »
These were quite large rings of ferrite ..rectangular in cross section.  They use to fit on the neck of cathode ray tubes in 405 line TVs.... Dismantled quite a few old TVs in my time and kept the magnets.   They were quite light..very similar to ferrite rods used in AM radios....very brittle.    I have a ferrite rod and it is 2/3 (as someone said) the weight of the a steel drill bit of a similar diameter plus or minus for fiddle factor as they are of different lengths.   The ring magnets may not be of quite the same material.  I have a broken bit of one somewhere..  Must be 40 years since they were used in tellies.
« Last Edit: 09/12/2007 20:54:11 by Pumblechook »
 

Offline daveshorts

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lightest vs strongest magnet
« Reply #19 on: 10/12/2007 10:56:05 »
There are two main ways of making a magnet, by putting a current through a coil, or by using a ferro-magnetic material. If you use a superconducting coil the current will keep going for a long long time, so it is essentially a permenant magnet.

If you are talking about ferromagnets then the simple answer is that they are extremely complicated. On the smallest scale they are magnets because they have unpaired electrons - so they have an electron 'orbiting' the nucleus in one direction without another orbiting in the opposite direction. This means the atoms are tiny electromagnets. Having this property means a material is a paramagnet. This means it has the capacity to be magnetic, but it will only magnetize weakly in a magnetic field and when you take the field away it stops.

The next stage is that in some materials,due to a wacky quantum mechanical effect, the atomic magnets like lining up so you get regions of the material with all the atomic magnets line up behaving like larger magnets. These areas are called domains. Normally they are randomly orientated, but if you apply a field they will tend to line up. The only elements that have this ferromagnetic property are iron, nickle and cobalt. These are all similar transition metals and so quite dense. It is possible to make ferromagnets out of mixtures of other elements.

How easily these domains can move affects how strong a magnet you can make. If you magnetise them and they can move easily then when you turn the field off they will randomise again leaving you with a very weak magnet. If however it is very hard to move the domains you can be left with a very strong magnet. So all the crazy alloys you get to make magnets are about making it very hard for the magnetic domains to move. At the moment the strongest magnets are neodymium, Iron, Boron  Nd2Fe14B and can produce over a tesla of magnetic field.

 

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lightest vs strongest magnet
« Reply #19 on: 10/12/2007 10:56:05 »

 

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