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Physics for Secondary Schools

magnetic fields, one due to the bar magnet and the other due to the Earth. Figures
3.51 illustrates the resulting field when the two fields combine. At certain location,
the Earth’s field neutralises the field due to the bar magnet. This results into neutral
points (x).
Magnetic
north
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x

x x

x

Figure 3.51: Fields of a bar magnet against the earth’s magnetic field
Angle of declination GNP
As mentioned earlier, the Earth’s Axis of rotation MSP
Magnetic North Pole (MNP) and Angle of
Geographic North Pole (GNP) are declination
not in the same plane. Generally, Geographical
the Earth’s axis of rotation does not equator
coincide with the magnetic axis as
shown in Figure 3.52. Magnetic
axis
Magnetic equator
The angle between the two axes
is called the angle of declination, MNP GSP
D or angle of deviation Figure 3.52: Angle of declination

Additionally, the Earth’s magnetic field changes slowly over time so that the MNP
moves. There have been times through the Earth’s 4.5-billion-year history that the
Earth’s magnetic field was completely reversed. Table 3.1 shows a list of the latitude
and longitude of the MSP for some years from 2001.

Table 3.1: Location of MSP for some years
Year 2001 2002 2003 2004 2005 2006
Latitude 81.3°N 81.6°N 82.0°N 82. 3°N 82. 7°N 86.50°N
Longitude 110.8°W 111.6°W 112.4°W 113.4°W 114.4°W 164.0°E

The angle of declination also indicates whether the magnetic south is east or west of
the geographic north.

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Student’s Book Form Two

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