Answer the following questions .
a. The earth's magnetic field varies from point is space. Does it also change with time ? It so , on what time scate 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 know about the earth's field in such distant past ?
e. The earth's field departs from its dipole 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 `10^(-12)` T, Can such a weak field be of any significant consequence ? Explain.
[Note : Exercise 2 is meant mainly to arouse your curiosity . Answers to some question above are tentative or unknown . Brief answers wherever possible are given at the end . For details , you should consult a good text on geomagnetism.]