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Magnetism is all around us. Magnets are not only found in everyday objects such as speakers, computers, televisions, and electric motors, but they also help in practical uses like navigation and simple household items. From crafting clasps to powerful machines, magnetism plays an important role in both science and daily life. In this article, we will explore the useful natural phenomenon of magnetism.
Magnetism is a physical phenomenon that occurs through a magnetic field, causing objects to attract or repel each other. You may have experienced this when playing with magnets. The north and south poles attract each other, but when the same poles face each other, they push away.
A magnetic field is an invisible physical field that surrounds magnetic materials. It exerts magnetic force on other moving charges or magnetic materials, dictating how magnetic objects attract, repel or interact over a distance without physical contact. You can see the magnetic field in action by sprinkling iron powder around a magnet. The powder would align along the field lines, revealing the shape of the field.
The lines in a magnetic field point from the North Pole towards the South Pole. The stronger the magnetic field, the more concentrated the field lines and more lines would appear in the diagram.
Not every material can become a magnet. Magnetic materials are usually metals and contain domains, tiny “mini magnets” that each have their own north and south pole. In an unmagnetised material, these domains point in random directions. In a magnet, however, the domains are aligned in the same directionthroughout the material. Their individual magnetic fields then combine to form a strong, unified magnetic field, giving the magnet a distinct north and south pole.
Now that we understand that magnetic materials are made up of domains, we can see how arranging these domains allows us to create a magnet. Remember that in a magnet, all the domains are aligned in the same direction. Therefore, to make a magnet from a magnetic material, we need to align its domains so that they all point in the same direction.
A magnetic material can be magnetised simply by being placed in the presence of another magnet’s magnetic field. This process, called magnetic induction, creates an induced magnet. When exposed to the external magnetic field, the magnetic domains within the material temporarily align in the same direction, giving the material temporary magnetic properties.
One example of magnetisation by induction is placing iron nails (or steel paperclips, anything made of a magnetic material) near a permanent magnet. The magnetic domains within the iron nail align with the permanent magnet’s magnetic field, temporarily turning the nail into a magnet that can attract other iron nails. However, once the permanent magnet is removed, the domains randomise again and the nail loses its magnetism
Stroking a piece of magnetic material with another magnet is another way to create a magnet. By rubbing a permanent magnet in the same direction repeatedly, the magnetic domains within the material align, generating a temporary or permanent magnet.
A strong magnet (an electromagnet) can be generated by passing direct current (DC) through a solenoid, which is a coil of wire. DC means electric current flows in only one direction. We can use the right-hand thumb rule (also called the right-hand grip rule) to determine the polarity of the magnetic field generated by the solenoid.
How do we use the right-hand grip rule? First, make a thumbs-up sign with your right hand. Then, curl your index to pinky fingers in the direction of the current flowing through the solenoid. Your thumb will point toward the North Pole!
Now, if a magnetic material is placed inside the solenoid, the magnetic domains within the material align with the magnetic field, causing it to become magnetised. Because this magnet is produced using electricity, it is called an electromagnet.
To make a magnet, we align the magnetic domains within a magnetic material. But what happens if we misalign and scramble these domains? The magnet becomes demagnetised because fewer domains remain aligned, resulting in a loss of magnetism.
You can disrupt the alignment of domains within a magnet through physical force or by using an alternating current (AC).
Physical force, such as hammering or heating, causes the magnetic domains within a magnet to misalign. Essentially, you are physically knocking these domains out of place! This is why magnets may become weaker over time. As they experience wear and tear, their domains gradually accumulate misalignments, reducing their overall magnetism.
If DC refers to a unidirectional current, then alternating current (AC) is an electric current that periodically reverses direction in an oscillating manner. We’ve learned that with DC, a solenoid produces a magnetic field that aligns magnetic domains.
But what happens if the current switches direction regularly? The magnetic field also constantly reverses direction, scrambling the domains and destroying their alignment. Therefore, subjecting a magnet to AC causes it to lose its magnetic properties
You might notice that some magnets, like the bar magnet we’ve played with, are constantly magnetised, while others, such as those in electronics, are only magnetised when the device is switched on. These are known as permanent and temporary magnets, respectively.
The magnetic domains in permanent magnets remain aligned for a long time, resulting in long-lasting magnetism. Permanent magnets are typically made of steel and other hard magnetic materials.
In contrast, the domains in temporary magnets do not retain their alignment for long and quickly lose magnetism once an external influence, such as another magnet or a DC source, is removed. These temporary magnets are usually made of soft iron or other similar materials.
You can use a temporary magnet like soft iron to store permanent magnets. These are known as keepers, and they prevent self-demagnetisation of the permanent magnet by shielding it from physical knocks and other magnetic fields, helping the magnet retain its magnetism over time.
Now that we have learned the basics of magnetism, let’s look at an example of how magnets revolutionised lives.
The compass has been used for navigation since ancient times. It is essentially a small magnet that aligns with a magnetic field. When you place a compass near a magnet, you can see that it turns to follow the magnet’s magnetic field lines.
The earth is a giant magnet, and has its own massive magnetic field that spans across the entire world. Compass needles align themselves to the Earth’s magnetic field, hence showing where the North Pole is.
However, remember that the North Pole of a magnet would be attracted to the South Pole, and hence point in that direction. If that is the case, then shouldn’t the direction the North Pole of our compass points towards be the South Pole?
Conventionally, when we refer to the North Pole, we are actually talking about the geographic North Pole. In reality, the geographic North Pole is actually the magnetic South Pole, and the geographic South Pole is the magnetic North Pole. That’s why a compass needle pointing toward the geographic North Pole is really being attracted to Earth’s magnetic South Pole.
In this article, we explored what magnetism is and how tiny domains within magnetic materials give magnets their properties. When these domains are aligned in the same direction, the material becomes a magnet; when they are misaligned, the magnetism is lost. Because the Earth itself acts like a giant magnet, understanding magnetism is essential for navigation, especially for how compasses work. By grasping these ideas, you can see how a basic natural phenomenon connects directly to everyday tools and technologies.
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Prepared by: Michelle
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