sci.physics.electromag

On Feb 28, 7:45=A0pm, Jim Black wrote:
> On Feb 28, 3:13 pm, Mike D wrote:
>
>
>
>
>
> > On Feb 28, 5:47 pm, Benj wrote:
>
> > > You guys know a lot. How about a quick and dirty answer for this one.
> > > I'm looking at some super strong magnets from United Nuclear.http://ww=
w.unitednuclear.com/magnets.htm
>
> > > The magnets are listed by size and lifting power. Say I'm going to buy=

> > > a rod magnet(s) in some length. The questions I want to answer is
> > > 1. What is the magnetic field right at the surface of the magnet (with=

> > > the magnet in free space)
>
> > > 2. How does the magnetic field fall off with distance on the
> > > centerline of the rod as you move away from the end surface.
>
> > > and
>
> > > 3, =A0What is the field as above if I place two magnets along the same=

> > > axis but spaced apart by some distance d. =A0(only interested in the
> > > field in the gap on the centerline, not in the whole field
> > > distribution around the magnets. )
>
> > > Of course eventually I'll just buy some of these since they are pretty=

> > > cheap and use a Hall probe to get the "real" answer, but it just
> > > seemed to me I could get a handle on this with just the magnet
> > > dimensions and the lifting force to help me decide what to order.
> > > Doesn't the lifting force equal something like BH/2 ?
>
> > > It almost seems to me that since the lifting force is per unit area
> > > that the field at the centerline and surface is independent of the
> > > diameter of the rods? Is that right?
>
> > > Thanks.
>
> > The quickest way to get an answer to 1 is to use one of the online
> > calculators. =A0For example:http://www.dextermag.com/CalculationList.asp=
x
> > Neo45 will have a Br of approximately 1.37 Tesla (13,700 Gauss)
>
> > For 2: The field generally drops as a function of the square of the
> > distance
>
> Make that the cube of the distance (at distances large compared to the
> size of the magnet); magnets are dipoles.
>
> --
> Jim E. Black- Hide quoted text -
>
> - Show quoted text -

I stand corrected. Thanks very much!

Best regards,
Mike