thinking about magnetics

[Borat]

i need somebody to tell me that i am not completely insane yet

i was thinking about magnetic fields for maybe err couple hours and came to this strange conclusion:

if you took a magnet of infinite size the magnetic field inside of it woudl be zero.

then if you carved out a hole inside of this magnet the field inside the hole would have same magnitude as an equal size magnet would in empty space - but reverse polarity.

now. is anybody here a doctor and can diagnose me ?

[JarreYuri]

Your thesis sounds right to me.
But that's just me making the model in my head.

[hoboham]

I’m not sure about that, magnetic flux isn’t charge i.e. a charged conductive sphere would have a zero voltage inside due to the equal amount of current on the outside, but with a magnet each domain is aligned in one direction giving the net effect, regardless. Inside of your sphere one end would have positive flux and the other opposite end would have negative flux

[tinitus]

Originally Posted by Borat

if you took a magnet of infinite size the magnetic field inside of it woudl be zero.

I dont think there is any "field" INSIDE a magnet
The field is created AROUND the magnet

Im not sure about it, but within certain limits it seems to me like a slightly wider field gap results in greater field strength, than a very narrow field gap

[jcx]

a good model for a permenant magnet is a sheet of surface current on the exterior with current direction normal to the polarization

this model clearly has interior magnetic field of opposite direction to the external field

all flux lines are closed loops so somewhere in the magnentic circuit the flux points in the opposite direction from the that of any reference point on the flux line loop

try poking around the HyperPhysics site:
http://hyperphysics.phy-astr.gsu.edu/hbase/HFrame.html

[Borat]

Originally Posted by jcx

a good model for a permenant magnet is a sheet of surface current on the exterior with current direction normal to the polarization

this model clearly has interior magnetic field of opposite direction to the external field

now try applying that model to a piece of magnet that doesn't have any exterior because it is infinite.

i can tell you what logic i used to arrive at the conclusion if you want but i don't guarantee it's correctness.

[tinitus]

Are you talking about the universe?

[Borat]

Originally Posted by tinitus

Are you talking about the universe?

you just made me think of a new way to prove it will be zero. let me give you both ways.

original proof:

if you integrate the field along any field line it will be zero because it forms a complete circle. therefore if you integrate along every field line of a magnetic dipole the sum will be zero as well. therefore if you integrate over the volume of the entire universe the field of one dipole it will be zero because you will have integrated over every field line. now if there is an infinite number of such dipoles which are uniformly spread in space then their combined effect on a single point in space by reflection will be the same as the effect of a single dipole on all of the points in space combined. therefore it will be zero and there will be no field.

second proof:

if the magnet is infinite it means the field must be uniform everywhere. this means the field lines always run parallel and are straight into infinity. this means they don't exist because a field line can only form a circle. therefore the field is zero.

[Borat]

that's more or less the principle behind this ribbon motor:



you can arrive at this motor using the logic described in this thread by starting with an infinite piece of magnet, cutting an infinitely long gap in it and then symmetrically trimming it off to manageable size.

you start with uniformity and then you use symmetry to maintain it.

if you do it right you are left with a 100% uniform gap field as in the above diagram.