Question -
Answer -
(a) The three independentquantities conventionally used for specifying earth’s magnetic field are:
(i)Magnetic declination,
(ii) Angle of dip,and
(iii)Horizontal component of earth’s magnetic field
(b)The angle of dip at apoint depends on how far the point is located with respect to the North Pole orthe South Pole. The angle of dip would be greater in Britain (it is about 70°)than in southern India because the location of Britain on the globe is closerto the magnetic North Pole.
(c)It is hypotheticallyconsidered that a huge bar magnet is dipped inside earth with its north polenear the geographic South Pole and its south pole near the geographic NorthPole.
Magnetic field linesemanate from a magnetic north pole and terminate at a magnetic south pole.Hence, in a map depicting earth’s magnetic field lines, the field lines atMelbourne, Australia would seem to come out of the ground.
(d)If a compass is locatedon the geomagnetic North Pole or South Pole, then the compass will be free tomove in the horizontal plane while earth’s field is exactly vertical to themagnetic poles. In such a case, the compass can point in any direction.
(e)Magnetic moment, M =8 × 1022 J T−1
Radius of earth, r =6.4 × 106 m
Magneticfield strength,
Where,
= Permeability of free space = 
This quantity is ofthe order of magnitude of the observed field on earth.
(f)Yes, there are severallocal poles on earth’s surface oriented in different directions. A magnetisedmineral deposit is an example of a local N-S pole.