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Physics for Secondary Schools
and south geographic poles as defined by pole. The compass needle points toward
its axis of rotation, and the north and the north pole, which means it will point
south magnetic poles that are defined toward the Earth’s MSP. Therefore, a
by its magnetic field. The magnetic compass needle points in the general north
pole in the Northern Hemisphere is direction of the Earth as shown in Figure
magnetically a south pole called the 3.46. For this reason, the magnetic north
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Magnetic South Pole (MSP), and in pole of the compass needle is referred to
the Southern Hemisphere, the magnetic as a north-seeking pole, and the general
pole is called the Magnetic North Pole direction it indicates is often called the
(MNP) as shown in Figure 3.45. “magnetic north".
Geographic Magnetic To earth’s To earth’s
north pole south pole geographic magnetic
north south
pole pole
Compass
north
magnetic
pole
Magnetic Geographic
north pole south pole
Figure 3.46: Magnetic compass
Figure 3.45: Earth’s geographic
and magnetic poles
When a magnet is hung so that it can
swing freely in a horizontal direction, it
Direction of the Earth’s magnetic field will move back and forth for a short time
Magnetic fields have both magnitude before it comes to rest in an approximate
and direction. The SI unit for magnitude N–S direction. The magnet comes to rest
of a magnetic field is the Tesla, T. The with its axis in a vertical plane called the
magnitude of the Earth’s field varies magnetic meridian.
from one location to another, ranging
from 25µT to 65µT. A compass may
be used to determine the direction of the
Earth’s magnetic field. A compass is a String
device with a magnetised needle that is
free to rotate in a horizontal plane and
align itself with the horizontal component
of the Earth’s magnetic field. The head
of a compass needle is a magnetic north
pole, and the tail is a magnetic south Figure 3.47: Freely suspended magnet
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Student’s Book Form Two
Physics Form 2 Final.indd 116 25/10/2025 10:27
