question_answer 17)

Answer the following questions: (a) Explain qualitatively on the basis of domain picture the irreversibility in the magnetisation curve of a ferromagnet. (b) The hysteresis loop of a soft iron piece has a much smaller area than that of a carbon steel piece. If the material is to go through repeated cycles of magnetization, which piece will dissipate greater heat energy? (c)‘A system displaying a hysteresis loop such as a ferromagnet is a device for storing memory.' Explain the meaning of this statement. (d)What kind of ferromagnetic material is used for coating magnetic tapes in a cassette player, or for building ‘memory stores' in a modern computer? (e)A certain region of space is to be shielded from magnetic fields. Suggest a method.  

Answer:

(a) Refer article 5.5. 1. and 5.7.1. of 'Dinesh New Millennium Physics- XII. (b) Heat dissipated per second is directly proportional to the area of the hysteresis loop so carbon steel piece will dissipate greater heat energy. (c) Magnetisation of a ferromagnet depends upon the applied field as number of cycles of magnetisation given to it. Thus the value of magnetisation can indicate the number of cycles of magnetisation a sample has undergone or in other words the memory with respect to the cycles stands stored in the sample. (d) Ceramics are used for this purpose. Ferrites which are specially treated barium iron oxides are commonly used. (e) The space to be shielded is enclosed by soft iron rings. The magnetic field lines remain confined in the ferromagnetic material of the rings and the enclosed space will be free from magnetic effect. Note. Magnetic shielding is not as effective as electrostatic shielding is.