As a bar magnet is generally referred magnets with cylindrical or cuboid form which have a magnetic north and south poles exactly. The magnetic poles typically lie along the longest axis of symmetry. The bar magnet has the strongest attraction at the poles and only low field strengths at the center of the bar.
A U-magnet is basically just a curved bar magnet . A disc magnet can also be viewed as a modification of a (cylindrical) bar magnet, in which the radius is greater than the height of the cylinder. The poles are also located on the top surfaces of the cylinder, i.e. on the top and bottom of the disk .
- Günter Springer: Expertise in electrical engineering. 18th edition, Verlag - Europa - Lehrmittel, Wuppertal, 1989, ISBN 3-8085-3018-9