Answer the following questions:
(i) The earth’s magnetic field varies from point to point in space. Does it also change with time? If so, on what time scale does it change appreciably?
(ii) The earth’s core is known to contain iron.
Yet geologists do not regard this as a source of the earth’s magnetism. Why?
(iii) The charged currents in the outer conducting regions of the earth’s core are to be responsible for earth’s magnetism. What might be the ‘battery’ (i.e. the source of , energy) to sustain these currents?
(iv) The earth may have even reversed the direction of its field several times during its history of 4 to 5 billion years. How can geologists know about the earth’s field in such distant past?
(v) The earth’s field departs from its dipole shape substantially at large distances (greater than about- 30000 km). What agencies may be responsible for this distortion?
(vi) Interstellar space has an extremely weak magnetic field of the order of ${{10}^{-12}}$ T. Can such a weak field be of any significant consequence? Explain
(i) Yes, the earth’s magnetic field varies from point to point in space and it also changes with time. It may change daily, annually of secularly with period of order of about 1000 yr. It may change irregularly during magnetic storms, etc. The time scale for appreciable change is about few hundred years.
(ii) The earth’s core contains iron but in the molten state. The molten iron is hot ferromagnetic material
in nature thus, it cannot be treated as a source of the earth’s magnetism.
(iii) The source of energy to sustain these currents may be the radioactive material in the interior of the earth.
(iv) During the solidification of certain rocks, it is recorded that the field was very weak. The analysis of these rocks may give the history of direction of field.
(v) The responsible reason for this distortion may be the
motion of ions in the earth’s ionosphere. The earth’s magnetic field may get modified by the field due to the motion of ions in atmosphere.
(vi) As we know that, when a charged panicle moves in a magnetic field, it moves along a circular path.
The necessary centripetal force is provided by the magnetic force.
As, B is less, r is more. So, in the interstellar space they move in a circular path of a large radius. Thus, the deflection in their paths becomes negligible.