Expert: Daniel Mazur - 4/8/2010

Question
when a permanent magnet is broken into two pieces ,one of the magnets 'poles change.why?how?what is the mechanism of this?

Answer
Hello Dhiaa,

poles don't change upon breaking a permanent magnet in two. All that happens is that instead of one magnet [N--S] (N for north and S for South pole) you end up with two magnets, each of which has both North and South poles. Consider that you break the magnet exactly between the original poles (I think this is the way you meant). Then the "equation" of the breaking is
[n--s][n--s] <= [N--S]
The lower case letters symbolize that while number of magnets (pairs of poles, dipoles) has doubled, each magnet has half the "strength".

Then we can consider breaking (cutting) a magnet ALONG the North-South direction and the "equation" of that will be
[n--s]
[n--s] <= [N--S]
Simply you just split the North pole in two and south in two as well, and each pair (each dipole) ends up with half the strength.

To understand why this is always so, you need to accept that the poles of magnets cannot exist alone (not in the real world, only in theories). Each magnet consists of individual atoms as their smallest chemical constituents, and even the atoms have their North and South. So, by breaking apart a big magnet you are not creating poles, you are merely making visible the poles that already were inside the material. Thus:

[n--s][n--s][n--s][n--s]   [n--s][n--s]   [n--s][n--s]
[n--s][n--s][n--s][n--s] = [n--s][n--s] + [n--s][n--s]
[n--s][n--s][n--s][n--s]   [n--s][n--s]   [n--s][n--s]

You can do the reverse experiment and put two identical magnets together in the [n--s][n--s]. The whole, the sum of the 2 magnets will behave exactly the same way as one [N--S] magnet.

I hope this explanation helps you.

Daniel