Magnetic Declination Video Lecture | Physics for JAMB

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and trying to know about the magnetic
elements of Earth what are the magnetic
elements offered what do we mean by
magnetic elements of earth magnetic
elements are nothing but then the
distance these are a set of three
quantities which describe the magnitude
and direction of Earth's magnetic field
completely they'll tell now I told you
only about the magnetic field lines of
the earth now there are certain
quantities which will appropriately and
accurately define the magnitude and
direction of the magnetic field of Earth
so those set of three quantities are
together known as magnetic elements of
Earth they basically define the magnetic
field of the earth so what are those
three elements they are magnetic
declination magnetic tip and horizontal
component so these three elements
together will define the math direction
as well as magnitude of magnetic field
of the earth right so we will try to
understand each of these elements one by
one so let us first know what is
magnetic declination now just now I told
you that as I mentioned earlier that the
geographic north and geographic south
are different from the magnetic north
and magnetic south so when I talk about
magnetic declination it is basically the
angle between Geographic north and
magnetic north so this angle is known as
the magnetic declination so it is
generally denoted by theta let us
suppose this is the true knot and this
is the magnetic not so this angle
would be your magnetic declination now
how will you know which is the magnetic
knot for example if you place what is
this this is nothing but your needle
right the magnetic compass needle so
when you place your needle the needle
will always point towards the
north-south direction right so the
direction pointed by the needle that
direction the angle which that direction
means with the true Geographic knot is
known as the angle of declination so
when you see it here then this angle
this axis and this axis the angle which
they make amongst themselves is known as
the magnetic declination right so
magnetic declination is greater at
higher latitudes and smaller near the
equator that means as now when you look
at this figure you might think that this
angle will remain the same whether I am
at the equator equator is somewhere here
right whether I am at the equator
all right go towards higher latitudes
that is as I go towards the poles also
this angle will remain the same but it
is not so that's because this axis that
is the true north axis this axis will
remain the same now when you are at the
equator at this point your magnetic
compass will point somewhere in this
direction let us suppose this is your
compass when you are at equator so this
will point almost towards your
geographic north right but as you keep
going higher like keep going to hide
your latitudes what will happen this
angle will keep increasing for example
as you go higher in the latitude let us
suppose you reach this point when you
when you reach this point your magnetic
needle will point towards the magnetic
north that means it will point somewhere
here right so this angle will increase
again when you reach this point it will
point here so if you see because you
will always measure that deflection of
the magnetic needle with respect to this
yellow axis which you see here this
yellow axis is the direction of true not
so when you are here so it will point
towards the magnetic not it is
this one so this will be your angle when
you go up it will point towards this
direction so this is your angle as you
go even above it will point towards this
direction then needed so this angle will
keep on increasing as you go higher in
the latitude that means when you are at
the equator the direction which is shown
by the magnetic needle that is same as
your true not almost same not exactly
same but at least almost same as your
true not but as you keep going up the
deflection shown by your magnetic needle
that keeps increasing and that is why
the angle with the geographic north also
keep increasing right so I hope it is
clear so as you keep moving up all your
keep moving down the the direction shown
by the compass will keep increasing
right like in like for example here it
is shown that the compass is placed here
so this is the angle now as you keep
increasing I mean as you keep going up
in latitude for example when you place
the same compass somewhere here so the
compass will again point like this for
example if I please this compass here if
this point is here in this case it will
point to this direction only because
your magnetic north is here that means
it will point like this so if you look
at this this angle and this angle so
your this angle will increase similarly
if you place the compass even higher so
the compass will point somewhat like
this so that means this angle will again
increase so that means as you keep
moving the compass upward the angle
between the true north and the North
shown by the magnetic compass keep
increasing so that declination is
smallest at near the equator
therefore places which are which are
equatorial that means which lie
somewhere near the equator for example
India India is a country which lies
somewhere near the equator so places in
India there if you place the magnetic
needle the direction shown by the
magnetic needle
is the same as the true north-south
direction so the magnetic needle aligns
itself in the north-south direction so
that north-south is the same as the true
north-south direction because the angle
between geographic north and magnetic
north is very less so it again that
means the angle of the magnetic
declination is denoted by theta and it
is the angle between the true geographic
North and the magnetic north this angle
is smaller near the equator and it
increases as we go towards the poles
that is as we go towards higher
latitudes the angle of declination keeps
increasing now while it increases I hope
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