To explain qualitatively the domain picture of the irreversibility in the magnetisation curve of a ferromagnet, we draw the hysteresis curve for ferromagnetic substance. We can observe that the magnetisation persists even when the external field is removed. This gives the idea of irreversibility of a ferromagnet.
(ii) As we know that, in hysteresis curve, the energy dissipated per cycle is direcdy proportional to the area of hysteresis loop. So, as according to the question, the area of hysteresis loop is more for carbon steel, thus carbon steel piece will dissipate greater heat energy.
(iii) The magnetisation of a ferromagnet depends not only on the magnetising field, but also on the history of magnetisation (i.e. how many times it was already magnetised in the past). Thus, the value of magnetisation of a specimen is a record of memory of the cycles of magnetisation, it had undergone. The system displaying such a hysteresis loop can thus act as a device for storing memory.
(iv) The ferromagnetic materials which are used for coating magnetic tapes in a cassette player or for building memory stores in the modern computer are ferrites.
(v) To shield any space from magnetic field, surround
the space with soft iron ring. As the magnetic field lines will be drawn into the ring, the enclosed region will become free of magnetic field.