(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 a 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.
Answer –
(a) The Earth’s magnetic field changes throughout time, and it takes a few hundred years for a significant shift to occur. The change in the Earth’s magnetic field over time cannot be overlooked.
(b) Because the iron core at the Earth’s core is molten and non-ferromagnetic, it cannot be regarded a source of Earth’s magnetism.
(c) Radioactivity in the earth’s interior is the source of energy that keeps the currents flowing in the earth’s core’s outer conducting areas. The earth’s magnetism is thought to be caused by these charged currents.
(d) The reversal of the Earth’s magnetic field has been observed multiple times in the past, approximately 4 to 5 billion years ago. During the solidification of rocks, these fluctuating magnetic fields were barely recorded. The investigation of this rock magnetism can provide information about the geomagnetic history.
(e) At long distances, the Earth’s field deviates significantly from its dipole shape due to the existence of the ionosphere. Because of the field of single ions, the Earth’s field is slightly altered in this location. The magnetic field that is linked with them is generated when they are moving.
(f) Charged particles travelling in a circle can be deflected by a relatively modest magnetic field. For a big radius path, this may not be detectable. The deflection can change the flow of charged particles when seen in the context of the vast interstellar space.