let us study 2 important terms. in. terrestrial
magnetism that is in the magnetic field of earth these are geographic and magnetic meridian.
let us first write down, about. these 2. terms. very first is geographic meridian. abut geographic
meridian we can write that, at any point. on earth surface. it is a vertical plane.
containing. true north-south direction. at that point. we’ll discuss it with the help
of. realistic situation also. but first write down the magnetic meridian. because it’ll
be easier to deal both of these simultaneously. about magnetic meridian we can say that at
any point. on earth surface. it is a vertical plane. containing. earths magnetic field.
and. magnetic axis. of earth. to understand both of these, lets have a look on the situation
here. you can see this is our earth, and here we are treating, this vertical line as its
axis of rotation. say if we consider a point p on the surface of earth. if we just zoom
into the picture we can see at point p if these are the directions north south east
and west. then north-south direction is the one. which is in a vertical plane which is
containing the earth’s axis of rotation. here you can see i have drawn a vertical plane.
or a diametrical plane of, spherical earth which contains earth axis of rotation. so
at any point on earth surface. this plane will also contain the true north-south direction
also. now if we consider the magnetic axis of earth we know it is at an angle approximately
11 degree tilted from the axis of rotation. and earths magnetic field exist. along this
axis like you can see these are the magnetic lines of earths magnetic field. then at this
point p where we have drawn . the north-south-east-west direction as these in the northern hemisphere
of earth. the magnetic field is getting into the earth surface at. the angle of the theta.
here if we zoom. into this picture we can see this is the direction of earths magnetic
field. and if we draw vertical plane which contain the. earths magnetic field. and if
we zoom out the picture you can see this vertical plane will also contain the magnetic axis
of earth. so this plane we define as magnetic meridian. and you can see the other plane
which we already considered which was containing the earth axis of rotation. this is termed
as geographic meridian. so these 2 vertical plane at a point on earth surface which will
always intersect at the point on earth surface. these planes are called geographic meridian,
and magnetic meridian.
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