Question

Use the domain theory to explain why a needle becomes magnetized by rubbing it in one direction with a strong permanent magnet

Answer 1

A magnetic domain is region in which the magnetic fields of atoms are grouped together and aligned
In an unmagnetized object, like the initial piece of metal like a needle , all the magnetic domains are pointing in different directions. But, when the metal became magnetized, when it is rubbed with a strong magnet, all like magnetic poles lined up and pointed in the same direction.
When we rubbed the magnet over the surface of the metal, some of the magnetic domains aligned and the metal became partially magnetized. When we rubbed the magnet over the metal a second time, more of the magnetic domains became aligned and the metal became a stronger magnet.
Thus the metal became a magnet. It would quickly become unmagnetized when its magnetic domains are returned to a random order.