Answer the following questions: (a) The earth's magnetic field varies from point to point in space.
Does is also change with time? If so, on what time scale does it change appreciably?
(b) The earth's corei s known to contain iron. Yet geologists do not regard this as a source of earth's magnetism, why?
(c) The charged currents in the outer conducting regions of earth's core are thought to be possible for earth's magnetism. What might be the battery 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 geologits know 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 30000km). What agencies may be responsible for this distortion?
(f) 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.

Explanation

(a) Earth's magnetic field chagnes with time. It takes a few hundred years to change by an appreciable amount. The variation in earth's magnetic field with the time cannot be neglected.
(b) Earth's core contains molten iron. This form of iron is not ferromagnetic. Hence, this is not considered as a source of earth's magnetism.
(c) Theradioactivity in earth's interior is the source of energy that sustains the currents in the outher conducting regions of earth's core. these charged currents are c onsidered to be responsible for earth's magnetism.
(d) Earth reversed the direction of its field several times during its history of 4 to 5 bilion years. These magnetic field got weakly recorded in rocks during their solidification. one can get clues about the geomagnetic history from the analysis of this rock magnetism.
(e) E arth's field departs from its dipole shape substantially at large distances (greater than about 30,000km) because of the presence of the ionosphere, In this region, earth's field gets modified because of the field of single ions. while in motion, these ions produce the magnetic field associated with them.
(f) An extremely weak magnetic field can bend charged particles moving in a cricle . this may not be noticeable for a large radius path. with refrence to the gigantic interstellar space, the defication can affect the pasaage of charged particles.