Page 110 - Physics_Form_2

Physics for Secondary Schools
FOR ONLINE READING ONLY
Figure 3.20: Double touch method
Activity 3.4
Aim: To magnetise a steel rod by
a single-touch method.
Materials: Steel rod, bar magnet, pins,
smartphone or tablet with
camera, tripod or phone
stand, video recording or
time-lapse app, computer
or smartboard
Procedure
1. Place the steel rod on a flat surface
and set up a smartphone or tablet
on a tripod to record the entire
magnetisation process.
2. Drag the pole of a bar magnet from
one end of the rod to the other.
3. After reaching the far end, lift the
magnet and return it to the starting
point.
4. Repeat step 2 ten times. The stroking
should involve wide loops.
5. After magnetising, use pins to test
for magnetism by hanging them one
below the other from the rod, and
record or photograph the result.
6. Use a computer or projector to
play back the video and analyse the
104
Physics Form 2 Final.indd 104
magnetisation process, highlighting
key actions and effects.
Questions
(a) Why must step 2 be repeated during
the magnetisation process?
(b) Why are wide loops important when
stroking with the magnet?
(c) Explain the significance of loading
the pins one below the other.
For each stroke, several dipoles align
themselves in one direction. Stroking
is repeated to ensure that a maximum
number of dipoles have aligned
themselves to such a level that the end
product is a magnet. A state where no
further alignment takes place is known as
saturation. A load of pins placed one after
the other is used to test for saturation. If
the magnet can hold the pins, then it has
reached its saturation. During stroking, a
wide loop is advised so that the alignment
of the dipoles is not disturbed.
The third method of magnetisation
relies on the fact that an electric current
produces a magnetic field. A long wire is
wrapped around an object, such as a nail
and connected to a battery as shown in
Figure 3.21. The direct current supplied
in the wire produces a magnetic field that
magnetises the nail. The combined effect
of all the turns of wire produces a field
similar to that of a bar magnet. A wire coil
of several turns is called a solenoid. To
increase the field strength of the magnet
formed by a solenoid, a soft iron core is
Student’s Book Form Two
25/10/2025 10:26