Page 149 - SCERT Kerala State Syllabus 8th Standard Basic Science Textbooks English Medium Part 1_Neat

Compass is a magnetic needle arranged in such a way that it
can rotate freely inside an aluminium or plastic case. When
placed on a horizontal surface the magnetic needle in it comes
to rest quickly in the north- south direction. Hence this
instrument is used to find the direction.

On the basis of the lesson, write down the method adopted
in ancient times by sailors on ships and travellers in the desert
to reach their destination.
Haven’t you seen that a bar magnet suspended on a string
lies in the north south direction? Why don’t the ends come
in other directions?

Earth as a Magnet

The earth acts like a large magnet. This was first
geographic north earth's discovered by the scientist William Gilbert. He found
magnetic south out that just as the earth has north and south
geographically, it has the north pole and the south
pole when considered as a magnet.

Towards which pole of the earth’s magnet does
the North Pole of the suspended magnet point?

What about the south pole of the bar magnet?
The south pole of the earth’s magnet is near the
earth's magnetic geographic north pole and the north pole of the earth’s
north geographic
south magnet is near the geographic south pole. (Figure 11.4)

Fig. 11.4
From the ideas you have gathered, write down in your
science diary why a freely suspended bar magnet using a
thread always align itself in the north south direction. Isn’t it
See 'magnet and compass' a property of magnets? Let’s have a look at the other
in PhET of IT@ School properties of magnets.
Edubuntu
Let's magnetise a hacksaw blade.

How does magnetisation occur?
Place the hacksaw blade AB on a table. Rub the north pole of the bar magnet
NS starting from the end A to the end B of the blade, as shown in fig.11.5.
Repeat it several times in the same manner. The hacksaw blade changes
into a magnet with the end A as the north pole and the end B as the south
pole.

148 Basic Science VIII