# I Non linear field of a long bar magnet

1. Dec 20, 2017

### shustrng

How can the "end effect " be reduced on a long Bar magnet where the (for example) North pole is along the length of the top side. For example a 0.5 cm square bar say 5" long is stuck (South) onto a metal backing. The center length of 4" has a linear field effect but the ends have a bloom presumably as the N/S pole fields overlap. For example a small washer can be placed anywhere along the middle (top side) and will stay where placed, but when slid to the end, and released, it jumps back a cm away from the end? Basically, this non-linear field is stronger attracting at these ends. It is desired to reduce this end effect.

2. Dec 20, 2017

If I understand your experimental observations, some of the magnetic flux lines in the north direction exit the magnet near the north pole, but before they reach the pole. As a result, a thin piece of iron placed on top of the magnet near the north pole will also become magnetized in the northerly direction. The result is you then have two north poles right next to each other and they will repel. Alternatively, if the piece of iron were introduced adjacent to the pole (on the endface), the magnetization would be such that the south pole end of the piece of iron would be adjacent to the north pole of the magnet, and it would stick to it. $\\$ I think I interpreted your observations correctly, but I don't know how to reduce the effect.