question_answer 1)

Answer the following questions regarding earth's magnetism:                 (a) A vector needs three quantities for its specification. Name the three independent quantities conventionally used to specify the earth's magnetic field.                 (b) The angle of dip at a location in southern India is about . Would you expect a greater or smaller dip angle in Britain?                 (c) If you made a map of magnetic field lines at Melbourne in Australia, would the lines seem to go into the ground 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 m magnetic moment 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?  

Answer:

                (a) (i) Angle of dip or magnetic inclination,                 (ii) Magnetic declination,                 (iii) Horizontal component of magnetic field of earth .                 (b) Yes, it is about in Britain because it is closer to the magnetic north pole of earth.                 (c) The magnetic field lines due to the magnetism of earth would seem to come out of the ground.                 (d) Compass can point in any direction because it is free to move in horizontal plane but at magnetic poles the magnetic field of earth is exactly vertical so there will be no horizontal component of the magnetic field to effect the compass.                 (e) Using the formula for magnetic field on the equatorial line of a magnetic dipole i.e.,                 we get                                                            This value tells the order of magnitude of magnetic field of earth.                 (f) Geologists are correct to think so because it is an approximation to consider the magnetic field of earth to be a single dipole field. The magnetised mineral deposits can be treated as local dipoles on earth.