Answer the following questions regarding
(a) A vector needs three quantities for
its specification. Name the three independent quantities
conventionally used to specify the
(b) The angle of dip at a location in
southern India is about 18º.
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?
field, it is claimed, roughly approximates the field due to a
dipole of magnetic moment 8 x
at its centre. Check the order of magnitude of this number in
(f ) Geologists claim that besides the
main magnetic N-S poles, there are several local poles on the
surface oriented in different directions. How is such a thing
possible at all?
(a) The three independent quantities
conventionally used for specifying
(i) Magnetic declination,
(ii)Angle of dip, and
(iii) Horizontal component of
(b)The angle of dip at a point depends
on how far the point is located with respect to the North Pole or
the 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 closer to the
magnetic North Pole.
(c)It is hypothetically considered that
a huge bar magnet is dipped inside earth with its north pole near
the geographic South Pole and its south pole near the geographic
Magnetic field lines emanate from a magnetic north pole and
terminate at a magnetic south pole. Hence, in a map depicting
field lines, the field lines at Melbourne, Australia would seem
to come out of the ground.
(d)If a compass is located on the
geomagnetic North Pole or South Pole, then the compass will be
free to move in the horizontal plane while
earth's field is
exactly vertical to the magnetic poles. In such a case, the
compass can point in any direction.
T - 1
Radius of earth, r=
Magnetic field strength,
= Permeability of
free space =
This quantity is of the order of magnitude of
the observed field on earth.
(f)Yes, there are several local poles
surface oriented in different directions. A magnetised mineral
deposit is an example of a local N-S pole.
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