question_answer 2)

Answer the following questions                 (a) 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?                 (b) The earth?s core is known to contain iron. Yet geologists do not regard this as a source of the earth?s magnetism. Why?                 (c)The charged currents in the outer conducting regions of the earth?s core are thought to be responsible for earth?s magnetism. What might be the ?battery? (i.e. the source of energy) to sustain these currents?                 (d)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 known about the earth?s field in such distant past?                 (e)The earth?s field departs from its dipole shape substantially at large distances (greater than about 30,000 km). What agencies may be responsible for this distortion?                 (f)Interstellar space has an extremely weak magnetic field of the order of . Can such a weak field be of any significant consequence? Explain.  

Answer:

(a)Although appreciable change can take a few hundred years yet change with time is very much there.                 (b) Molten iron has temperature more than Curie temperature so it is not ferromagnetic in nature.                 (c) Probably radioactivity (i.e. emission ofandparticles from the nuclei) present in the interior of earth is responsible for it.                 (d) During solidification of some rocks, the magnetic field of earth gets weakly recorded in these rocks. Geomagnetic history of these rocks can be traced by making analysis of such rocks.                 (e) Ionosphere of earth consists of charged ions. Motion of these ions causes a magnetic field which affects the magnetic field of earth at large distances from earth. The magnetic field due to ions depends upon extra terrestrial disturbances like solar wind.                 (f) At very-very large distances like interstellar distances the small fields can significantly affect the charged particles like that of cosmic rays. For small distances, the deflections are not noticeable for small fields but at very large distances the deflections are significant.                 [clearly small value of B gives a very large value of radius R]