The earth's field departs from its dipole shpae substantially at large distance (greater than about 3000 km). The responsible factor for this distortion is

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.]

A short bar magnet of magnetic moment 5.25xx10^(-2)JT^(-1) is placed with its axis perpendicular to the earth's field 's field direction . At what distance from the centre of the magnet the resultant field is inclined at 45^@ with earth's field on (a) its normal bisector and (b) its axis. Magnitude of te earth's field at the place is given to be 0.42 G, Ignore the length of the magnet in comparison to the distance involved.

The geostationary orbit of the earth is at a distance of about 36000 km from the earth's surface. Find the weight of a 120 kg equipment placed in a geostationary satellite. The radius of the earth is 6400 km.

A short bar magnet placed in a horizontal plane has its axis aligned along the magnetic north - south direction . Null point are found on the axis of the magnet at 14 cm from the centre of the magnet . The earth's magnetic field at the place if 0.36 G and the angle of dip is zero. What is the total magnetic field on the normal bisector of the magnet at the same distance as the null point (i.e., 14 cm) from hte centre of the magnetic ? (At null points , field due to a magnet is equal and opposite to the horizontal component of earth's magnetic field.)

The electric field intensity due to infinite cylinder having charge q per unit length and radius R at a distance r that is greater than R from its axis is

A bar magnet of magnetic moment 2.0 A m^2 is free to rotate about a vertical axis through its centre. The magnet is released from rest from the east-west position. Find the kinetic energy of the magnet as it takes the north-south position. The horizontal component of the earth's magnetic field is B = 25 muT .

The maximum focal length of the eye lens of a person is greater than its distance from the retina. The eye is

Find the distance of a point from the earth's centre where the resultant gravitational field due to the earth and the moon is zero. The mass of the earth is 6.0xx10^24 kg and that of the moon is 7.4x10^22 kg. The distance between the earth and the moon is 4.0xx10^5km .

Answer the following questions regarding earth's magnetism. a. A vector needs three quantities conventionally used to specify the earth's magnetic field. b. The angle of dip at a location in southern India is about 18^@ . Would you expect a greater or smaller dip angle in Britain ? c. If you made a map of magnetic field lines at Melboune in Australia, would the lines seem to go into the groung or come out of the ground ? d. In which direction would a compass free to move in the vertical plane point to , if located right on the geomagnetic north or south pole ? e. the earth' s field, it is claimed roughly approximates the field due to a dipole of magnetic moment 8 xx10^(22)JT^(-1) located at its centre. Check the order of magnitude of this number in some way. f. Geologists claim that besides the main magnetic N - S poles, there are several local poles on the earth's surface oriented in different directions. How is such a thing possible at all ?