Re: wondermagnets

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Jim Lux <jimlux-at-earthlink-dot-net> 

At 12:06 PM 3/11/2004 -0700, you wrote:
>Original poster: Terry Fritz <teslalist-at-twfpowerelectronics-dot-com>
>
>Hi Jim,
>
>At 10:23 AM 3/11/2004, you wrote:
>>At 07:24 AM 3/11/2004 -0700, you wrote:
>>>Original poster: Terry Fritz <teslalist-at-twfpowerelectronics-dot-com>
>>>
>>>Hi Steve,
>>>
>>>I friend of mine has a magnetron (in his basement). I think he said the 
>>>magnet was about 1 Tesla.  The Magnets from the store seem to be "rated" 
>>>at 1.2 Tesla.  So I would guess they are about the same but the 
>>>Magnatron electromagnets in general covers more area.  His machine is 
>>>also very small compared to some.
>>>
>>>Cheers,
>>>
>>>         Terry
>>
>>
>>Flux - (Weber (Volt second) ) (in CGS, Line or Maxwell)(Capital 
>>Phi)  (compare Current)
>>
>>Flux Density (magnetic induction) - Tesla (Weber/sq m), Gauss (CGS) 
>>(Capital B)  (compare current density Amps/square meter)
>>
>>Magnetomotive Force - Gilbert(CGS) Amp-turn (SI), (compare to Voltage)
>>
>>Magnetic field strength (Magnetizing force)   - ampere/meter (no SI unit) 
>>(Oersted CGS)) (Capital H) (compare E field Volts/meter)
>>
>>
>>mu (permeability) = B/J  (Gauss/Oersted) (Tesla/(amp/meter))
>>
>>In an electromagnet, as you put more magnetic field (i.e. by cranking up 
>>the current in the coil around the material) into something, the flux 
>>increases until it reaches some maximum, and then the flux can go no 
>>higher (around 1.8-2T for iron/steel)
>>
>>Some materials ("hard") will still have flux, even after the field is 
>>gone.  You can then put an opposite field on it and the flux will 
>>steadily decrease.
>>
>>So.. that magnet rated at "1.2 Tesla" actually means that at some place, 
>>the field is 1.2T.
>
>I barely have "electric" fields figured out, let alone the magnetic stuff 
>%:o))
>
>So a 1.2T magnet could be the size of a car, or the size of a pin head...

Exactly... The "pole pieces" in, for example, a loudspeaker, take the flux 
from a fairly large magnet and squeeze it down into a smaller area (where 
the coil is).  The total flux remails the same, but the flux density is 
higher in the air gap.   At 1 Tesla, you could use steel or iron for the 
polepieces.  You could have a big magnet that has a flux density of, say, 
300 mT at the faces and make that 1T in a gap with 1/3 the cross sectional 
area.