Attraction and repulsion
What is magnetism?
Magnetism is an invisible, non-contact force exerted by an object to attract or repel another object. Attraction is the force that pulls an object towards another, while repulsion is the force that pushes an object away from another. Compare this to gravity, which only attracts objects.
All atoms have one or more electrons orbiting its nucleus. The movement of the electron/s around the nucleus produces a slightly magnetic field. In non-magnetic substances, the random arrangement of atoms cancels out any magnetic forces produced by the electron orbits, making the substance non-magnetic.
In magnetic substances, the electron orbits are aligned in one direction, giving the substance its magnetic qualities. The orbits in metals such as iron, nickel and cobalt, tend to align in groups called domains, which is why these substances are often magnetic.
North and south
The domains align so that they point in two directions called poles, one north and one south. A compass is a type of magnet that aligns itself according to the Earth's magnetic field, showing north and south. We will explain more about the Earth's magnetic field next chapter.
Attraction and repulsion
There are two basic rules for magnets:
- unlike poles (different poles) attract each other; and
- like poles (same poles) repel each other.
This means a north pole and a south pole will attract each other while a north pole will repel a north pole and a south pole will repel a south pole.
We have already introduced the concept of force fields for non-contact forces. A magnetic field is a force field in which the attractive and repulsive forces of a magnet operate. The force field of a magnet is not linear but emitted in a curved pattern because each magnet has both a north pole and a south pole.
You can witness the shape of a magnetic field by pouring iron filings on a piece of paper and then placing the magnet underneath the paper. The filings will align according to the force of attraction and repulsion in the field.
The closer the lines, the stronger the force. The strongest parts of a magnet are at its poles. Refer Image 1
Creating and destroying magnets
Some substances are naturally magnetic, while others can be made magnetic by aligning its domains along a north-south axis. You can make an unmagnetised piece of iron magnetic by using a magnet to align its domains, gently tapping its domains into alignment or placing it in an electromagnet, which will align the domains. We will go into further depth about electromagnetism in the next chapter.
You can experiment with magnetism with a magnet and a small piece of iron or steel, such as a pin. Use either pole of a bar magnet and stroke along the pin a number of times. Make sure you stroke with the same end, in one direction only. By doing this you create a temporary magnet and you can now use the pin to attract another pin.
Magnets that retain their magnetic force are permanent magnets. You can destroy magnets by knocking their domains out of alignment or by heating them, making the atoms become excited and disordered, scrambling their alignment. Most permanent magnets are made from harder substances that have a high heat tolerance, so that it is more difficult to destroy the domain alignment.