I also have a paper with electromagnetic theories about light that I thought were great before I was persuaded—James Clark Maxwell
Electromagnetism is a great discovery. Modern inventions, from microwave ovens to mobile phones to maglev trains, are all based on the principles of electromagnetism. Each of these everyday devices contains some very complex electronics, transistors, semiconductors, transformers, and so on. But, despite the incredible complexity, these functions can be solved almost entirely by the four simple equations proposed by James Clark-Maxwell that brilliantly explain electricity and magnetism, or collectively call electromagnetism.
The first equation, while very simple, can be scary at first. So let's break it down into several parts. The " B " here represents the magnetic field at a point in space , but what is a magnetic field?
Let me make this clear first. Have you ever used a refrigerator magnet? Have you ever noticed how quickly it "escapes" from your hands and sticks to the surface of the refrigerator when approaching it? This can't happen on its own, so there must be something in the air that makes the refrigerator magnet drawn onto the refrigerator. This "thing" is what we call a magnetic field, in other words, it is the area around a magnetic substance (refrigerator magnet) that can exert force on another magnetic object (the surface of the refrigerator). This magnetic field is the factor that determines the force, so the stronger the magnetic field in a place, the stronger the force. If you look closely, you must also notice that it is always glued in a particular direction, and there are two special places that tend to be attracted more "tightly", these two places are what we call the poles of the magnet (north and south). The magnetic field around the magnet is not evenly distributed, and we have to express this with something. We express this force in terms of something called a magnetic field line, and the magnetic field line of a refrigerator magnet looks like this.
The two poles of the strongest magnetic field are the places where the magnetic field line is most dense, in other words, the denser the magnetic field line, the greater the force. This is what the " B " in Maxwell's equations does. This is a mathematical equation that expresses the strength of a magnetic field and the direction in which it acts, i.e. it is a vector. This simple equation makes a lot of sense, it helps us interpret the direction and the strength of the force acting on an object close to the magnet.
Now that we understand this part of the equation, let's move on to understanding what the inverted triangle represents. It's what we call divergence. When we relate it to fluid flow, it becomes much easier to understand divergence. Consider a bathtub with taps and outlets in the bathtub as shown in the image below.
Turn the faucet on and the drain as well. The water flow seen from above must have been like this. The small arrows painted around represent the flow of water. Here, we ignore any reflections from the side of the bathtub. The arrow at a certain point points in the direction of the water flow at that point, so there may be a range of speeds in the bathtub. Therefore, if you consider the flow of water, for example, the yellow circle in the middle of the bathtub, the amount of water flowing in will also flow out, so the dispersion of the water flow of this yellow circle will be zero.
Now consider the maroon circle and orange circle around the end of the faucet. The water flowing into the brown circle also flows out, so the net flow rate is zero; similarly, the net flow rate of the orange circle is also zero. You might ask, if the divergence is always zero, what's the point?
In fact, in other cases, the divergence is not always zero, first consider a very simple case: a light bulb, around the bulb there is a similar imaginary ball, you can know, the light emitted from the bulb directly out of the sphere, where the dispersion of the light emitted around the sphere is positive! But is there also a negative divergence? Exist, a vacuum cleaner! Consider having an imaginary sphere around the vacuum cleaner that pulls dust particles onto itself, so when we calculate the overall dispersion of dust around the vacuum cleaner, the result is negative! This is the negative divergence.
Now that we have a vague concept of " B " and " inverted triangle " , we can begin to understand Maxwell's first equation. The equation says that the divergence or net current of the magnetic field is always zero, regardless of the location or chosen magnetic material. Let's review the experiment with the bathtub and get the field line back in the refrigerator magnet for a better perspective.
Consider the orange-red circle on the right side of the magnet, and you'll see that the incoming magnetic field will also flow out, but does this hold true for every point? Let's take a look at the circle near the magnetic pole of the bar magnet, which at first appears to be a "source".
While this may seem like a "source," it is not, and there is no actually a magnetic field line flowing from the South Pole to the North Pole. So if we follow the actual magnetic field lines, as shown in the figure above, taking into account the overall space, you will see that the sum of the net flows is still zero for all points around the magnet. If you look closely, you'll notice how similar bathtubs and magnets are when comparing their respective magnetic field divergences. Thus, this equation shows that the net magnetic field flow at any point in space is zero, regardless of where the magnet is.
This has some very serious implications. This means that there is no magnetic monopole. Or to put it another way, a magnet always has an north pole and an south pole.
Many studies have found evidence of the existence of magnetic monopoles, but to date, none have been confirmed. But if one day a magnetic monopole is discovered, it will mean that Maxwell's equations are wrong and our understanding of electromagnetism is wrong. This will usher in a new era in physics!