Joining poles of bar magnet What happens when 2 poles(i.e. noth and south) of the same bar magnet joined to each other to form circular loop?
 A: bridging the gap between the poles of a magnet means that most of the field lines are captured inside the body of the magnet to form endless loops that do not extend outside- and it stops attracting other magnetizable objects. 
A: A pole, in mathematics, is a point at which a function is singular
(undefined/infinite/divide-by-zero).   A good mathematical approximation of
the external field of a bar magnet is the combination of two
singular functions, one positive and one negative, whose
singular points lie near the tips of the bar.
In that "dipole" approximation, the result of bending the bar so that
the poles meet is that the field everywhere vanishes (because
the negative and positive functions cancel).   That's a good match
for what would happen in the real world, where the external field of the
ring magnet becomes negligible; unless you were to attempt
to alter the magnetization (reversing the internal field, for instance), there's no way to know it's a magnet.
Core memory used such ring magnets, to hold data in early
computers.   There's an energy stored in the internal
magnetization, that can be used to read out the sense, clockwise
or counterclockwise, of a ring magnet field.
Oddly, for symmetry reasons, the dipole approximation is
accurate in the ring-magnet limit, but has subtle deviations
from the real field from a bar magnet: square poles, with corners,
aren't characterized correctly by any two-pole function.
