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Magnetism
Concept sheet | Science and Technology
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Secondary
1-2
Magnetism is a characteristic property of a substance that has the ability to be attracted or repelled by a magnet.
Hematite (iron ore) is a magnetic substance.
Fluorite is a non-magnetic substance.
Hematite rock
vvoe, Shutterstock.com
Fluorite rock
igsin, Shutterstock.com
The magnetism of a substance can be tested practically by bringing it close to a magnet.
Magnets
A magnet is an object or device that has magnetic forces able to repel or attract certain objects. Magnets are made of ferromagnetic elements such as iron |\text{(Fe)},| cobalt |\text{(Co)},| nickel |\text{(Ni)}|, or an alloy of these metals.
Although their shape and size vary, magnets always have a north pole and a south pole.
The north pole of a magnet is the pole that naturally points towards the Earth's geomagnetic north pole (near the Earth's geographic north pole). On the magnet, it is often identified by the letter N and the colour red.
The south pole of a magnet is opposite to the north pole. On the magnet, it is often identified by the letter S and the colours blue ou white. It can also have no colour at all.
Magnets of various shapes and sizes
Law of magnetic poles
All around a magnet, magnetic forces exert an effect on other magnets and on nearby ferromagnetic substances. This invisible area bounding the range of a magnet is called the magnetic field.
The magnetic field of a magnet cannot be seen with the naked eye, but the effects of the law of the magnetic poles can be observed:
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There is an attraction between two magnets when different poles are close to each other;
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There is a repulsion between two magnets when two like poles are close to each other.
The different poles (north and south) of these two magnets attract each other. These magnets attract each other.
Attraction between two magnets
The like poles (north-north or south-south) of these two magnets repel each other. These magnets undergo repulsion.
Repulsion between two magnets
Since the needle of a compass is a magnet, observing its behaviour in the vicinity of another magnet allows the identification of its magnetic poles.
Here is a U-shaped magnet with unidentified poles.
Bring a compass to one end of the U-shaped magnet and observe the needle’s behaviour.
The north pole of the compass is attracted to the end of the U-magnet.
Based on the law of the magnetic poles, we can say that this side of the U-shaped magnet is definitely a south pole (north-south attraction).
Since a magnet always has a north pole and a south pole, the other end of the U-shaped magnet is inevitably a north pole.
Behaviour of a compass near a U-magnet