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 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 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 5.2 is meant mainly to arouse your curiosity. Answers to some questions above are tentative or unknown. Brief answers wherever possible are given at the end. For details, you should consult a good text on geomagnetism.]
a)
It is given that Earth’s magnetic field changes with space. It also changes with time. However, it may take a few hundred years to change by an appreciable amount. But even on a much smaller time scale of few years, this variation in earth’s magnetic field with the time cannot be neglected completely.
b)
Earth’s core is known to contain iron, yet, geologists do not regard this as a source of the earth’s magnetism because the iron in the earth’s core is in molten form. This form of iron is not ferromagnetic. Hence, it cannot be considered as a source of earth’s magnetism.
c)
The charged currents in the outer conducting regions of the earth’s core are thought to be responsible for earth’s magnetism. The source of energy to sustain these currents may be coming from the radioactive reactions going on in the interior of the earth’s core.
d)
The earth may have even reversed the direction of its field several times during its history of 4 to 5 billion years. Geologists can know about the earth’s field in such distant past because the earth’s magnetic fields get recorded weakly in the rocks as they solidify. Geologist can get clues about history of earth’s magnetism by studying these rocks.
e)
Earth’s field departs from its dipole shape substantially at large distances (greater than about 30,000 km ) 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 of their own hence distorting the earth’s overall field.
f)
Interstellar space has an extremely weak magnetic field of the order of 10 -12 T . This extremely weak magnetic field can bend charged particles moving in a circle. This may not be noticeable for small distances but over a large path, the deflection can affect the passage of charged particles like cosmic rays significantly.
a)
It is given that Earth’s magnetic field changes with space. It also changes with time. However, it may take a few hundred years to change by an appreciable amount. But even on a much smaller time scale of few years, this variation in earth’s magnetic field with the time cannot be neglected completely.
b)
Earth’s core is known to contain iron, yet, geologists do not regard this as a source of the earth’s magnetism because the iron in the earth’s core is in molten form. This form of iron is not ferromagnetic. Hence, it cannot be considered as a source of earth’s magnetism.
c)
The charged currents in the outer conducting regions of the earth’s core are thought to be responsible for earth’s magnetism. The source of energy to sustain these currents may be coming from the radioactive reactions going on in the interior of the earth’s core.
d)
The earth may have even reversed the direction of its field several times during its history of 4 to 5 billion years. Geologists can know about the earth’s field in such distant past because the earth’s magnetic fields get recorded weakly in the rocks as they solidify. Geologist can get clues about history of earth’s magnetism by studying these rocks.
e)
Earth’s field departs from its dipole shape substantially at large distances (greater than about
f)
Interstellar space has an extremely weak magnetic field of the order of
