what exactly is magnetism?like in electricity we can say that electrons and protons are responsible?how can it be justified?
Magnetism is also caused by electric charges, but they have to be moving.
James Clerk Maxwell showed that electricity and magnetism are two aspects of the same phenomenon in the 19th century.
Wikipedia has an article on electromagnetism, but the math is not for beginners.
Both electricity and magnetism are transmitted by photons. While electrons (and holes*) may flow through electric devices it’s the electric field that is doing the work. Protons are bound in atoms and are not involved in everyday electricity.
Some (many) particles have an electric charge. No particles have a magnetic charge. IIRC one of Maxwell’s equations implies this (goes of to read Mapcase’s link.) There it is, Gauss’ law for charge, no monopoles.
- a hole is where an electron isn’t
Yes and no. A moving electrical charge creates an (orthogonal) magnetic field, but magnet fields such as those developed by permanent magnets, can also be created by movement and interaction of electrons at the quantum mechanical level, which isn’t motion as we think of it. Here’s the Wikipedia main article on magnetism (different from Exapno Mapcase’s link) which is a good starting point for understanding the different manifestions of magnetism. You’ll have to get into Maxwell’s equations to really understand the mechanics of electromagnetism, but reading up on the differnt “types” of magnetism will get you started without a lot of fussy math.
Stranger
Tell that to an electrochemist. Protons, or rather, cation (ionic atoms or molucules with a positive charge) play a significant role in chemical reactions which create electric currents.
Leptons and quarks are the two fundamental constituants of normal matter, and both they (and their antiparticles) have electrical charges. (Leptons have whole or “elementrary” charges–those of value 1 or -1–while quarks have fractional charges and therefore are under normal conditions always confined within other particles like protons and neutrons to satisfy elementary charge summation.) Other exotic particles have been suggested which may have electrical charge properties–elementary or fractional–but have not been demonstrated to actually exist.
The lack of magnetic monopoles is actually a little troubling, symmetry-wise, and many have suggested that they do or should exist but for various reasons are highly unstable and decay into magnetically neutral particles. This is still an open, though not currently highly active, field of investigation in particle physics and cosmology. See dyons. There’s no real known reason magnetic monopoles can’t exist, but we just haven’t found them or any definitive signs of them. Pity; it would make life much easier for anyone trying to control magnetic fields.
Stranger
It continues to fascinate me that so many everyday phenomena are absolutely impossible to explain or understand without resorting to mathematics or concepts that most people cannot or do not comprehend. A simple question such as “What, exactly, is magnetism?” cannot be definitively answered unless one starts delving into forces and fields that, according to Stranger, may not exist or “should” exist, or whatever. At least, there are aspects of the idea that aren’t totally understood. Of course, I understand that we are never at the total end of our understanding of anything, but it is such and interesting paradox that such a common and apparently simple and familiar experience such as magnetism should be such a mystery. Gravity, too. Ya know?
It’s often the simple questions that lead one to very complicated issues. Unlike “direct” electromatic repulsion between physical objects (er…touching), magnetism seems to offer what the kind of remote interaction that so squigged out Newton. To resolve this we create this notion of invisible fields or particle interactions, and the math and theory behind that predict what happens in the real world sufficiently that we accept it as truth, but to claim that this comprises genuine understanding is misleading at best.
We (most of us, except for the very rare and highly twisted genuises) can only understand phenomena as interpreted in terms of past experience, hence the inclination to explain fundamental forces and interactions in terms of particles, waves, et cetera. Because, like all analogies, these break down at a certain level, we tend to view these failures as paradoxes when in truth, they’re a failure of our ability to properly understand. A magician’s slight of hand seems like a great mystery, too, until you see the trick demonstrated. Then it’s just a “I didn’t realize you could do that,” revelation.
Fun stuff, indeed.
Stranger
I’m sure that someone smarter than me will come along to correct me if I’m wrong, but it seems to me to be a problem of scale.
The thing is, the “mechanics” (for lack of a better word) that produce phenomenon like gravity and electromagnetism occur on a scale MUCH smaller than we can directly observe. Our intuitive “understanding” of the world is in large part formed when we’re young. When we get into thinking about things that occur outside of our ability to directly observe them it’s not uncommon for our findings to conflict with what we intuitively believe is the way the worlds works.
In short, things happening on a very small scale don’t appear to follow the “rules” we’re familiar with.
Well, there’s this gang called the Pros…
More accurately, no known particles have a magnetic charge. As my advisor is fond of describing the situation: Magnetic monopoles definitely exist. There might just be a very small number of them, like zero. That is to say, it’s very probable that magnetic monopoles were formed in the Big Bang, but under many models, their expected density is approximately one in a volume the size of the observable Universe.
zoid, one can accurately say that the underlying mechanics of electromagnetism occur on a very small scale, but the situation is a bit different with gravity. The quantum-mechanical aspects of gravity are completely unknown at this point, even by specialists. Our best current models for gravity depend not on microscopic phenomena, but on the geometry of space-time. Of course, non-Euclidean geometry is probably just as unfamiliar to laymen as are Hilbert operators, so the point remains that they don’t follow what most think of as “the rules”.
This is a serious problem. People tend to think that common everyday phenomena must have simple understandable explanations. And when they don’t, then tend to turn on scientists for making things “complicated.” Or talking in a strange language. Or for making their brains work.
Ya know what? Nothing has a simple explanation. Nothing deep about our universe can be explained simply and without mathematics. Our “common sense” understandings are wrong. It’s not a plot by scientists. It’s the way the world is.
It’s also the reason that people keep turning to “god” as an explanation - because it is simple and they never have to go beyond that.
Doesn’t matter that this explanation explains nothing and can’t be used to make anything happen. Ya want it simple? Ya got simple. Just be sure ya take the consequences as well.
Really? So if I built me a room with lead walls thick enough to stop virtually all photons, would my compass not know how to find magnetic north?
The electromagnetic field can be alternately expressed as a flow of photonic fluid, but this makes for some very convoluted explanations in QED in order for it to all wash out nicely; otherwise, you have to go back to some version of luminiferous aether, and nobody wants to go there. It’s this sort of thing that drives physics undergrads to heroin addiction during their third-year E&M sequence.
To answer your specific question, the lead would somewhat attenuate the magnetic field in an analogous manner to how thick glass refracts light but it doesn’t terminate the field lines; to do so would result in a magentic point charge which, as already noted, is not readily found in nature (so far as we’ve seen). [post=6467723]Here[/post]'s an old thread on the topic.
Stranger
Um, Okay. But would my compass work?
Probably. The Earth’s magnetic field is quite strong, and in absence of any other magnetic influences, even an attenuated field would still orient the needle.
If you tried it, though, I’d wrap a big coil of copper wire around your bunker and alternate a current through it just to screw with you. 
Stranger
Mapcase, I hope you don’t take my little aside as a rant against science. It’s simply an observation. I’m not turning on anyone, but merely commenting that our everyday existence is bound by experiences that appear to be simple and commonplace - things falling down, for example. And we wonder why things appear to be attracted to the earth, and with a little more sophisticated observation, why things seem to be attracted to each other. It’s a great question. And it seems very simple. The fact that the answer is so extremely complex, so complex that no one really has an answer, is fascinating. The fact that when things get very far away they apparently start pushing away from each other instead of pulling seems pretty weird, too. It’s all very amazing and just makes our every day existence seem to have levels of complexity that are not apparent at first glance - it’s just quite fascinating, life.
You may be taking it lightly as an observation about life, but it remains, in fact, a deep and serious problem. Not to mention one that I’ve been thinking a lot about lately, hence my rant.
The question really is: why should we imagine that there are simple explanations to anything? We’re talking about the basic forces of the universe. That we can say anything about them at all, even in our most complex math, is amazing. It could easily be that we would have no idea of how anything worked when dealing with issues this deep.
Instead, we have a vast disconnect between those who want simple explanations and those who understand that just achieving any understanding requires a lifetime’s work. It’s a real societal issue and will remain so until the general public accepts that the way the universe works is not something that can be handled in a paragraph on a message board, but that it’s not an insult to them to say so.
Au contraire, mon fraire. I’m not necessarily looking for an easy or simple answer. But I don’t know why I have to rule one out. And I don’t know why you should automatically assume that the answers are so deep that they are automatically beyond us all. I understand that in our examination of these forces and factors that we have gotten denser and denser, until now the discussions have left virtually everyone behind. The conversations are in languages and terminology that almost no one follows. String theory and multiple dimensions are child’s play these days. That’s old hat. But at some point, maybe someone will come back to something simpler. Maybe. All I’m saying is that complexity is not necessarily the only answer. A deep and serious problem? And why is that? What rests on our understanding? A child’s life? I’m wondering about all this now.