A PRIMER ON MAGNETS
In this post, I will be talking about magnets, magnetic properties and will answer some fascinating questions like, from where the magnet gets its magnetic characteristics? how can we make a permanent magnet? does magnetic monopole exist? etc.
According to Greek legend, magnetism was first discovered by a shepherd named Magnes, who lived in Magnesia, Greece. Magnes was herding his sheep through the mountains. Suddenly he noticed the ferrule of his stick and nails in his sandals got stuck to a rock. The iron in his stick and nails had become attracted to the magnetic rock. The stone was named as magnetite, after the name of the shepherd or the country it was found in. It was also known as loadstone because of its attractive properties. Magnetite is one of the three natural occurring oxides of iron. It gets attracted to magnets and can be easily magnetized to form a permanent magnet. Naturally magnetized pieces of magnetite are called loadstone.
So as we now know where the word ‘magnet’ came from, let’s dig deeper into magnets.
What is a Magnetic Field?
In layman terms, a field is a region in which each point is affected by a force. The field is specifically named after the force which affects each point in space. Thus, a gravitational force affects each point in the gravitational field. An electromagnetic force affects each point in the electromagnetic field. An electric force affects each point in the electric field. Similarly, a magnetic force affects each point in the magnetic field.
You cannot see or touch this field under normal conditions but you can observe its effects on an object, example needle deflecting when a current is passed through a wire, a metallic object being attracted, like poles of bar magnet being repelled, etc. Electric currents produce magnetic fields, thus, we can define a magnetic field in terms of electric current that generates it.
Figure 1 is what we observe when we pierce a flat sheet with a wire carrying current (i) and spread iron filling on the flat sheet. Here we could clearly see the magnetic lines of the magnetic field. As we increase the current (i) the magnetic field strength (H) increases and as we increase the distance from the center (r), the magnetic field strength (H) decreases. Therefore, we can formulate a magnetic field strength (H) as follows:
This is the Ampere’s law in its most general form.
What’s the Origin of Magnetism?
Magnetic moment (M) helps us to understand the origin of the magnetic field. It would be safe for me to mention that the origin of the magnetic field is abstract to understand, however, we could identify the particle which technically is the origin of the magnetic field. By definition, the magnetic moment (M) is a vector that characterizes the magnet’s overall magnetic properties. Magnetic moment (M) is formulated by assuming an electron revolving around a positively charged nucleus as follows:
M = – L(e/2m)
Where e is the charge, m is the mass and L is the angular momentum of the electron revolving around a positively charged nucleus. The negative sign indicates that the orbital angular momentum of the electron (L) is opposite in the direction of the orbital magnetic moment (M).
The circular orbit of electrons produces an orbital magnetic moment. In additional to orbital magnetic moment, the electron has an intrinsic magnetic moment called spin magnetic moment. However, it does not mean that the electron is spinning as it does not have an axis to spin around like earth. The microscopic roots of magnetic can be traced back to this spin magnetic moment. The spin magnetic moment of the nucleus is way less than the spin magnetic moment of an electron. You may also verify this result by applying the above formula of the orbital magnetic moment. Therefore, it’s the electron which mainly originates the magnetic field in an atom.
Does Magnetic Monopole Exist?
A magnetic monopole is one of the fascinating science mystery. Paul Dirac mathematically showed that if magnetic monopole i.e. a hypothetical elementary particle with single magnetic charge exist, then, all electric charge in the universe must be quantized. Today, we are certain about the existence of quantized electric charge, however, physicists are still in search of magnetic monopoles. Other theories like the grand unified and superstring too predict the existence of magnetic monopoles.
One of the best theories in the era of physics is the theory of electromagnetism which is governed by Maxwell’s equations predicts, that, magnetic monopoles do not exist. Thus, the existence of magnetic monopoles will ruin one of the best theories in physics. Nevertheless, it was pointed out by Pierre Curie, that, magnetic monopoles could conceivably exist, despite not having been seen so far. Therefore, it’s still unclear whether magnetic monopoles exist or not. What do you think? Let me know down in the comment section.
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