Answer the following questions:(a) Explain qualitatively on the basis of domain picture theirreversibility in the magnetisation curve of a ferromagnet. (b) The hysteresis loop of a soft iron piece has a much smaller areathan that of a carbon steel piece. If the material is to go throughrepeated cycles of magnetisation, which piece will dissipate greaterheat energy? (c) ‘A system displaying a hysteresis loop such as a ferromagnet, isa device for storing memory?’ Explain the meaning of thisstatement. (d) What kind of ferromagnetic material is used for coating magnetictapes in a cassette player, or for building ‘memory stores’ in amodern computer? (e) A certain region of space is to be shielded from magnetic fields.Suggest a method.
a)
Consider the magnetization curve of a ferromagnetic material.
It is observed that when the magnetizing current H is zero, the actual magnetic flux density B is still greater than zero. Hence the magnetism persists even when the magnetizing current is removed. This reflects the irreversibility of the ferromagnetic material.
b)
The heat dissipated by a magnetic material as it goes through repeated cycles of magnetization depends on the area of its magnetization (B-H) curve. Since the magnetization curve of the soft iron piece has a smaller area than the carbon steel piece, the carbon steel piece will dissipate more heat.
c)
‘A system displaying a hysteresis loop such as a ferromagnet is a device for storing memory’. This statement means that the value of magnetization of a given material can be used as a record to store some information if the information bits can be made to correspond to these cycles. Since the magnetization curve is not just a single value function of magnetizing field; its value for a particular field depends both on the field and also on the history of magnetization.
d)
The ferromagnetic material used for coating magnetic tapes in a cassette player, or for building ‘memory stores’ in a modern computer is ceramics also known as ferrite.
e)
To shield a certain region of space from magnetic fields, the region could be surrounded by soft iron rings. In such kind of arrangement, the magnetic field lines will be drawn into the soft iron rings since they offer the least reluctance path to the magnetic field lines. However, unlike the perfect electric shielding of a cavity in a conductor placed in an external electric field, this arrangement is only approximate.
a)
Consider the magnetization curve of a ferromagnetic material.
It is observed that when the magnetizing current
b)
The heat dissipated by a magnetic material as it goes through repeated cycles of magnetization depends on the area of its magnetization (B-H) curve. Since the magnetization curve of the soft iron piece has a smaller area than the carbon steel piece, the carbon steel piece will dissipate more heat.
c)
‘A system displaying a hysteresis loop such as a ferromagnet is a device for storing memory’. This statement means that the value of magnetization of a given material can be used as a record to store some information if the information bits can be made to correspond to these cycles. Since the magnetization curve is not just a single value function of magnetizing field; its value for a particular field depends both on the field and also on the history of magnetization.
d)
The ferromagnetic material used for coating magnetic tapes in a cassette player, or for building ‘memory stores’ in a modern computer is ceramics also known as ferrite.
e)
To shield a certain region of space from magnetic fields, the region could be surrounded by soft iron rings. In such kind of arrangement, the magnetic field lines will be drawn into the soft iron rings since they offer the least reluctance path to the magnetic field lines. However, unlike the perfect electric shielding of a cavity in a conductor placed in an external electric field, this arrangement is only approximate.
