Page 108 - Physics_Form_2

Physics for Secondary Schools

If atomic dipoles arrange in such a way that N poles of all the dipoles face in one
common direction, the material is said to be magnetised.

Magnetisation is the process of aligning the atomic dipoles in a material in one
direction to produce a net effect of attraction or repulsion.
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The domains may show a net magnetic behaviour in the absence of an external
magnetic field. On applying an external magnetic field, all dipoles align themselves in
the direction of the applied field. In this way the material is strongly magnetised in the
direction parallel to the magnetising field as shown in Figure 3.17.

External
magnetic field

Figure 3.17: Aligned atomic dipoles in a magnetised material

Materials in which it is possible to cause eventually become aligned. Many natural
this alignment are either ferromagnetic or magnetic materials start out as part of
paramagnetic. Ferromagnetic materials lava (molten rock). If the lava contains
such as steel, nickel and cobalt can form ferromagnetic minerals, the atoms align
permanent magnets, while paramagnetic with the Earth’s magnetic field which is
materials such as aluminium and subject to vibration while the rock is still
chromium can only be weakly magnetised liquid. As the rock cools and solidifies,
and do not retain any magnetism once the the alignment becomes permanent.
external field is removed. The alignment
of domains in these materials can be
achieved through one of the following: Activity 3.3
heating or vibration, stroking, and the Aim: To demonstrate magnetic
electric method. alignment

In the first method of magnetisation, Materials: a small glass or plastic
an external magnetic field is required. jar, iron filings, bar
Placing an object in an external magnetic magnet, magnifying
glass (or smartphone
field will result in some degree of with magnification app),
alignment. Vibrating or heating the object computer or tablet with
can increase the amount of alignment by image analysis software
causing the atomic dipoles to move and

102
Student’s Book Form Two

Physics Form 2 Final.indd 102 25/10/2025 10:26