The earth has a strong magnetic field around it. It is
because the earth itself behaves like a strong magnet with its north and south
poles of the magnet in reverse with the geographic north and south of the
earth.
The entire earth magnetic field can be resolved into
horizontal and vertical components. Magnetic meridian is a vertical plane that
connects the north and south of the earth.
The angle between magnetic meridian and geographic north and
south is called angle of declination. Its value at the equator angle of
declination is approximately seventeen degree.
The angle between horizontal component and the vertical
component of the earth magnetic field is called angle of dip or inclination.
This value varies between zero and ninety degree. At magnetic meridian it is
zero degree and at the poles its value is ninety degree. The lines joining the
points with same dip are called isoclinical lines.
Apparent dip
The angle made by a magnetic needle with the horizontal component
of the earth magnetic field is called apparent dip. We can get to a conclusion
as shown in the diagram below.
Intensity of the magnetic field is defined as the magnetic
field strength per unit permeability of free space or medium. It is a vector
quantity and has similar direction of magnetic field strength.
Intensity of Magnetization is defined as the magnetic moment
per unit volume.
Magnetic susptability is
defined as the ratio of intensity of magnetization to the magnetic intensity.
It is a scalar quantity and it has no units and dimensions.
We can find the relation between susptability and relative
permeability as shown in the diagram below.We can express the total magnetic field strength as the
vector addition of horizontal and vertical components of the earth magnetic
field. By simplifying it further we can get the relations as shown in the
diagram below.
Potential energy of a bar magnet
Let us assume a bar magnet placed in the magnetic field. We
need to do some work in rotating it from one position to other. This work done
will be stored in the format of potential energy after the work is done.
The small amount of work done is defined as the dot product
of torque experienced by the bar magnet and the small angle it got turned. To
get the total work done, we shall integrate the equation and certain limits are
applied. Thus we are able to measure the total work done and that itself is
equal to the potential energy of the system.
Its value varies depending on the angle from where to where
it is turned. Its value vary if we are starting rotating the magnet from the
original or the earth magnetic field itself. We can also measure the work done
if we are moving in a turn around way that is rotating it in opposite
direction.
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