Re: comprehending electric/magnetic interactions

[Brian Whatcott <betwys1@SBCGLOBAL.NET>]

I will not pretend to explain a concept to an educator:
that role properly subsists with another educator.
I can however mention two ideas, as they appear to me.

1) The SI definition of electric current is sometimes
given as a force of a particular magnitude acting between two
parallel wires of infinite length and given separation,
each carrying a current of given
magnitude, the force acting perpendicular to their length.

2) A popular image which acts as a mnemonic of sorts
has a one turn coil with current flowing in the rotation
indicated by the letter "N" or letter "S" providing a
magnetic force equivalent to that of a permanent magnet
at the pole corresponding to each letter.

When such coils are placed co axially, there will be repulsion
or attraction in the direction of the axis of rotation.
When such coils are placed side by side, one  expects a force
to act perpendicular to that axis, so they move laterally,
closer or further apart.

If one can accept this rendering of forces due to currents in
wires, then it seems to me one can conform the case mentioned
 below by Gary to these three known cases.

Brian Whatcott      Altus OK

At 02:05 PM 7/1/2003 -0700, Gary Turner, you wrote:
> Could anyone help me explain this problem that arose during a discussion
> of magnetic field interactions.
>
> Consider a simple current loop.  It will produce a magnetic field and, if
> brought into an opposing magnetic field (in such a way that the external
> field is perpendicular to the plane of the loop), should be repelled by
> it.  Now, square the loop up and take three of the sides out of the region
> of magnetic field.  Now all that remains is a current-carrying wire in a
> magnetic field, which will be pushed to the side (F=qvxB).
>
> Indeed, a simple F=qvxB calculations shows that the loop will be
> either "stretched" or "compressed" depending on the direction of the
> current instead of being attracted towards, or repelled from, the source
> of the external magnetic field.
>
> It seems that the one side remaining in the field should still have a
> repulsive force - if it does not apply to any one side, how can it apply
> to the whole - but that would imply that there exists a force parallel to
> the magnetic field in addition to the qvxB.  This would have to hold
> equally for a long conductor just sitting in a magnetic field.
>
> Anyone out there considered this?