Imagine that in a rectangular region of empty space between the magnetic poles of a large horseshoe magnet, the magnetic field is essentially uniform and points directly downward, but is zero outside the region's boundary. The four vertical sides of the rectangular region are in empty space. We can easily imagine such a field, but such a field is in fact physically impossible.

Question

Quizplus · Accepted Answer

This is because magnetic field lines must form closed loops, originating from the north pole and terminating at the south pole of a magnet. A field that is uniform in a region and zero immediately outside without a smooth transition or closed loops violates this fundamental property of magnetic fields.

Imagine That in a Rectangular Region of Empty Space Between