Plane of core memory
mtapley at swri.edu
Fri Apr 19 09:19:20 CDT 2019
> On Apr 18, 2019, at 11:18 PM, dwight via cctalk <cctalk at classiccmp.org> wrote:
> Although, after written, there is little magnetism lost out side of the ring, while being magnetized, there is quite a bit of stray magnetism. By placing the the rings at 90 degrees, it minimizes the magnetism induced in the adjacent ring. The fields follow the inverse square law so the effect drops off quite quickly. Also the ring tend to pull the magnetic field into the ring, at least until saturated. At that time the field can leak into a neighbor and flip its state. Not being aligned with the direction of the ring also minimizes this stray field.
… inverse cube (?) … depending on the geometry you are talking about?
Real physicists please set me right if I have this wrong, but I think only radiating and static point fields (like electric or gravitational) from a finite source fall off as inverse square. That’s easy to see, it’s the same effect crossing the total area of a sphere centered at the source. Area on the sphere goes up like square of radius, so intensity has to go down like the square.
Magnetic field (from a finite source) I think goes down like the cube of the distance - north and south poles of the source tend to cancel better as the apparent angle between them gets smaller, in addition to the above effect. (That is a mnemonic, not a real explanation.)
On the other hand, if you were talking about field around a wire with current in it (a non-finite source, at least locally), then it *is* inverse square for the magnetic field, where inverse square refers to distance from the axis of the wire.
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