Non-Destructive Testing (NDT) Practice Test

When a bar magnet is cracked but not completely broken, how many poles will exist within that bar magnet?

1. 2

2. 3

3. 4

4. 6

The correct answer is: 4

When a bar magnet is cracked but not completely broken, the fundamental property of magnets comes into play, which is that they always have a north and south pole. When a magnet is divided, each fragment, regardless of its size, continues to exhibit its own north and south poles. In the case of a bar magnet that is cracked, even though the magnet appears to be a single piece, the crack introduces a new interface where the magnetic field lines can emerge. This results in the creation of additional poles around the crack. The number of effective poles would increase in accordance with the number of segments created by the crack. Thus, if the bar magnet is cracked into three pieces, for example, each piece would maintain its two poles, and the sections created by the crack itself can create additional poles in proximity to the fracture. The principal takeaway here is that the presence of a fracture in a magnet introduces complexities that increase the number of poles observed, leading to the conclusion that multiple poles can exist in a cracked magnet. Given this understanding, the total number of magnetic poles resulting from the fracture is equal to the inherent poles of the magnet plus the poles created due to the crack. This accumulation can lead to a misleading but technically accurate perspective on the number of