Take the 2-minute tour ×
Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free, no registration required.

Why do bar magnets have the least attraction in its center?

share|improve this question
add comment

1 Answer

up vote 3 down vote accepted

Their field lines look like this:

enter image description here

You see that the field lines near the center are parallel to the length of the bar. Moreover, the density of the field lines on the picture is maximized at the "poles" of the bar magnet and minimized at the center which means that the magnitude of the magnetic field is smallest at the center, too.

It's not hard to see why the field lines look approximately as those on the picture above. For an infinitely long magnet, the magnetic field would be fully confined to the cylinder - think of an infinitely long solenoid which essentially has the same magnetic field as a bar magnet. For a bar magnet of a finite length, the field lines ultimately split behind the poles but they're still comparably strong over there.

On the other hand, the field outside the bar, and far from the poles, is only nonzero because of some subleading effects; it would vanish for an infinitely long solenoid - that's why the field is so small over there.

share|improve this answer
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.