Contents
The study of Physics Topics involves the exploration of matter, energy, and the forces that govern the universe.
What are the Different Types of Artificial Magnets? What is a Magnetic Axis?
Natural Magnet
Magnetite, a black stone found in nature is called natural mag-net. It has two specific properties—
(i) attractive property and
(ii) directive property.
(i) Attractive property: Magnetite is found to attract pieces of iron.
(ii) Directive property: If a piece of magnetite is suspended freely with the help of a thread, it aligns itself in the north- south direction.
Navigators used magnetite as a compass for guiding their ships and hence it was called leading stone or lodestone.
The two above-mentioned properties are called magnetic prop-erties and the phenomenon is known as magnetism. Bodies showing these properties are called magnets.
Magnetism is a physical property of matter because when a body is magnetised, no chemical change occurs.
Artificial Magnet
Magnets found in nature have no definite shape. So the directive property cannot be understood clearly. Moreover, the attractive
power of this magnet is weak and hence is not so useful. Later artificial magnets have been invented for practical use. Using some special processes magnetic properties can be built up in iron, steel, nickel and some alloys. This process is known as magnetisation and the magnets thus made are known as artifi-cial magnets.
There are different shapes and sizes of artificial magnets. These are,
- bar magnet [Fig.(a)];
- magnetic needle [Fig.(b)];
- horse shoe magnet [Fig.(c)];
- ball-ended magnet [Fig.(d)] etc.
North and South Poles of a Magnet
If a bar magnet is dipped into some iron filings and then with-drawn, a good amount of filings clings at the two ends of the magnet but almost none at its middle [Fig.].
So, attractive power is maximum at the two ends of the magnet, and these two regions are called poles of a magnet. The middle portion, where no attraction is observed, is called the neutral region.
If a bar magnet is suspended freely by a thread, it sets itself at rest in the north-south direction. The pole of the magnet which always faces north is called the north pole (IV-pole) or positive pole. Similarly the pole facing south is called the south pole (S-pole) or negative pole of the magnet.
The line joining the two poles of a magnet is called magnetic axis. If a magnet is suspended freely from its mid-point, it comes to rest after some time. The imaginary vertical plane through the magnetic axis of the magnet at this position is called the magnetic meridian of that place.
Usually poles are considered as points and these two points lie very close to the ends of the magnet [Fig.]. The effective length of the magnet is about 80 – 85% of its geometrical length.
If different magnets are dipped into iron filings and withdrawn, the amounts of iron filings collected are not the same in all cases. So, the attractive power of different magnets are different, but there is no difference between powerful and weak magnets in respect of the directive property.
Mutual Action between Two Magnetic Poles
If the N-pole of a bar magnet is brought near the N-pole of a magnetic needle, repulsion occurs between them, i.e., the N- pole of the magnetic needle moves away from the bar magnet [Fig.].
Again, if the AT-pole of the bar magnet is brought near the S-pole of the magnetic needle, they attract each other, i. e., the S-pole of the magnetic needle comes closer to the bar magnet.
If the experiment is performed with the S-pole of the bar magnet, the opposite action is observed, i.e., the S-pole of the bar magnet attracts the IV-pole of the magentic needle but repels its S-pole.
Inference: Like poles repel each other but unlike poles attract each other.
Repulsion is the conclusive test of magnetisation:
If a body is repelled by a magnet, it is sure that the body is a magnet.
If one end of a body is brought near the N-pole of a powerful magnet and if an attraction is observed between them there are two probabilities:
- the body may be an ordinary piece of iron or
- the body is a magnet and the end under investigation is the S-pole of that magnet. So, attraction cannot identify whether a body is a magnet or not.
But if repulsion instead of attraction is observed in the above experiment, it is definite that the body is a magnet and the end under investigation is the N-pole of that magnet.
Hence, repulsion is the conclusive test of magnetisation.