frankywashere Posted February 14, 2018 Posted February 14, 2018 So i'm trying to understand magnetic fields, and I thought the way this video explained it was really interesting. He explains that if you look at a magnetic field as a "solid" it helps make sense of it. Because in essence a magnetic field is a SOLID object, but it's invisible. There's no real energy there, only what you put into it. So if you push opposing magnets together, one magnet isn't "pushing" the other, you're actually pushing it with an invisible object.But, why then can a magnet literally "pull" another magnet to it? Especially if it's a solid.Hope I explained this question properly.
Strange Posted February 14, 2018 Posted February 14, 2018 The trouble is, analogies only work in a limited way. So describing the field as "solid" might be helpful in explaining how they push, but that's about it. And I don't think it is very helpful then because the presence of another magnet (or even magnetic material) will deform the magnetic field, so it isn't really solid. Magnetism is caused by moving electric charges. It is just a fact of life that opposite charges attract and similar charges repel. There are various ways of describing this mathematically, but they don't really say "why" it happens. 1
frankywashere Posted February 14, 2018 Author Posted February 14, 2018 Ah thanks so much for explaining this! Ok now this leads me to my next question. I have a friend of mine that wants to try an experiment. This experiment will fail and he knows it too, but there's 1% of him that believes it may work. I do not believe it will work period because it violates the law of conservation. His idea is this. He believes that if he gets a electromagnetic induction device like those shaker flash lights, and he mounts several of them to a large disc, and then rotates that disk, the shakers will generate current. Now he thinks that by push starting this device he could hook up a motor, and the motor would only need to give the device a smaller push to keep it going since the device would already have momentum working. Just like a car already moving, doesn't need as much power to keep it going once it's already moving, he thinks the motor won't need much power to keep the device spinning. He thinks because of this, the "shakers" will generate enough power to power the motor plus a bit excess. He's trying to calculate the power of each shaker, the mass of the whole unit and the momentum. Could someone please explain why this is stupid and will not work? He thinks because gravity is helping spin the machine that it's somehow different than perpetual motion. Frank
StringJunky Posted February 14, 2018 Posted February 14, 2018 8 minutes ago, frankywashere said: Ah thanks so much for explaining this! Ok now this leads me to my next question. I have a friend of mine that wants to try an experiment. This experiment will fail and he knows it too, but there's 1% of him that believes it may work. I do not believe it will work period because it violates the law of conservation. His idea is this. He believes that if he gets a electromagnetic induction device like those shaker flash lights, and he mounts several of them to a large disc, and then rotates that disk, the shakers will generate current. Now he thinks that by push starting this device he could hook up a motor, and the motor would only need to give the device a smaller push to keep it going since the device would already have momentum working. Just like a car already moving, doesn't need as much power to keep it going once it's already moving, he thinks the motor won't need much power to keep the device spinning. He thinks because of this, the "shakers" will generate enough power to power the motor plus a bit excess. He's trying to calculate the power of each shaker, the mass of the whole unit and the momentum. Could someone please explain why this is stupid and will not work? He thinks because gravity is helping spin the machine that it's somehow different than perpetual motion. Frank There are losses in any closed system - friction will cause losses dissipated as heat, for example.
studiot Posted February 14, 2018 Posted February 14, 2018 (edited) I haven't watched the video, but I hope he did not offer the common fallacy. Magnetic fields do not push by themselves. Experiment. Place an ordinary bar magnet on a slippery table surface. Now bring the north pole of another bar magnet towards the north pole of the bar magnet. What do you observe to happen? What do you deduce from this observation? Edited February 14, 2018 by studiot
physicsismylife Posted February 14, 2018 Posted February 14, 2018 I've tried to explain the source of magnetism and it's mechanics in one of my movies: I hope, that it will help you to understand the magnetic fields...
frankywashere Posted February 14, 2018 Author Posted February 14, 2018 No, fact, he was pointing that fallacy out by using the analogy that magnetic fields are "solids" and don't actually do anything unless you give some input energy.
physicsismylife Posted February 14, 2018 Posted February 14, 2018 Maybe insted of "solid", we should use in this case the term "static" or "potential"?
frankywashere Posted February 14, 2018 Author Posted February 14, 2018 6 minutes ago, studiot said: Oh true. that makes sense.
studiot Posted February 14, 2018 Posted February 14, 2018 1 minute ago, frankywashere said: Franky, Please put your comments outside the quote box or this happens. Were you not going to say any more?
studiot Posted February 14, 2018 Posted February 14, 2018 8 minutes ago, frankywashere said: No, fact, he was pointing that fallacy out by using the analogy that magnetic fields are "solids" and don't actually do anything unless you give some input energy. You have the wrong 'fallacy' What did you make of my experiment? 1
physicsismylife Posted February 14, 2018 Posted February 14, 2018 Quote Magentic fields do not push by themselves. There's no kinetic force, which would work on itself. Every kind of field remains static, until we won't disturb it's balance of energy. Energy remains stored in matter in the form of potential kinetic force, which this matter can induce on other matter. To turn a potential field into kinetic one, we need to introduce somekind of test mass
studiot Posted February 14, 2018 Posted February 14, 2018 Was your question answered? You did say you are trying to understand magnetism.
physicsismylife Posted February 14, 2018 Posted February 14, 2018 (edited) Quote Magnetism is caused by moving electric charges. It is just a fact of life that opposite charges attract and similar charges repel. There are various ways of describing this mathematically, but they don't really say "why" it happens. Not really. Magnetism is created by alignment of magnetic polarities. In the case of subatomic particles, the source of whole magnetism, is the quantum spin. Charged particles are being aligned by electric currents - and this is why, they create a magnetic field. But EM induction works as well in the opposite way: a pernament magnet can create an electric current, when it moves around a conductor. Electric charge and the quantum spin are two, separate properties of matter... Edited February 14, 2018 by physicsismylife
Bender Posted February 14, 2018 Posted February 14, 2018 40 minutes ago, physicsismylife said: Not really. Magnetism is created by alignment of magnetic polarities. In the case of subatomic particles, the source of whole magnetism, is the quantum spin. Charged particles are being aligned by electric currents - and this is why, they create a magnetic field. But EM induction works as well in the opposite way: a pernament magnet can create an electric current, when it moves around a conductor. Electric charge and the quantum spin are two, separate properties of matter... You are either confusing or wrong. Moving charges and quantum stuff are two causes for magnetic fields. The former is eg the case for an electromagnet, the latter for a permanent magnet.
JohnMnemonic Posted February 14, 2018 Posted February 14, 2018 Quote Moving charges and quantum stuff are two causes for magnetic fields. The former is eg the case for an electromagnet, the latter for a permanent magnet. Moving charges = quantum stuff. Electric current = aligned stream of electrons Domains of a pernament magnet are created when the valence electrons in ferromagnetic material are aligned by the orientation of spin. All properies of matter have their source in "quantum stuff". You can't say, that something is different in micro and macro scales - it's only smaller... Because of the quantum spin, electrons can be treated, like tiny magnets...
Bender Posted February 15, 2018 Posted February 15, 2018 (edited) What about alpha particles? They have zero spin. Are you suggesting they shouldn't cause a magnetic field when moving? With "quantum stuff", I refer to phenomena that can only be explained with QM, not ordinary stuff like the magnetic field of a moving charge. Edited February 15, 2018 by Bender
JohnMnemonic Posted February 27, 2018 Posted February 27, 2018 (edited) On 15.02.2018 at 7:03 PM, Bender said: What about alpha particles? They have zero spin. Are you suggesting they shouldn't cause a magnetic field when moving? With "quantum stuff", I refer to phenomena that can only be explained with QM, not ordinary stuff like the magnetic field of a moving charge. Alpha particles have no magnetic moments, as the spins of protons and neutrons cancel eachother out. Funny thing is, that free neutrons have magnetic moments, despite their lack of electric charge. Magnetic field of a moving charge can be explained only with QM. In standard concept of electromagnetism, EM induction has no explanation - it just happens, but no one knows why... If you want to understand electromagnetism you HAVE to deal with QM - sorry, but there's no other way... https://www.coursera.org/learn/particle-physics/lecture/kniQc/4-3-spin-and-magnetic-moment "...There's no movement associated with any of those moments, let alone the rotation..." Edited February 27, 2018 by JohnMnemonic
Bender Posted February 27, 2018 Posted February 27, 2018 1 hour ago, JohnMnemonic said: If you want to understand electromagnetism you HAVE to deal with QM - sorry, but there's no other way... Does QM explain why an electron has a charge or a magnetic moment? What about the deflection of a beam? Do I need QM to understand that? After all, all mechanical forces are basically QM effects.
JohnMnemonic Posted February 27, 2018 Posted February 27, 2018 (edited) Quote Does QM explain why an electron has a charge or a magnetic moment? Actually, there's no explanation, why subatomic particles have any properties at all - magnetic moment, electric charge or mass. There's nothig solid and determined in QM... Personally, I think, that everything, what matters, is the information, "written" in particles... Quote What about the deflection of a beam? Do I need QM to understand that? It depends, if you speak about a stream of solid objects, or about a concentrated and polarized wave... Of course in QM, both can be actually the same... Quote After all, all mechanical forces are basically QM effects. Yes... And this is the biggest problem of physics, as a whole - because ... my first answer in this comment... Edited February 27, 2018 by JohnMnemonic
Bender Posted February 27, 2018 Posted February 27, 2018 17 minutes ago, JohnMnemonic said: Actually, there's no explanation, why subatomic particles have any properties at all - magnetic moment, electric charge or mass. There's nothig solid and determined in QM... Personally, I think, that everything, what matters, is the information, "written" in particles... So QM cannot explain magnetism after all. My example of the deflecting beam was poorly worded. I was referring to the mechanical deformation of a structure. My point is: I can explain the working of EM devices perfectly without QM, just like I can explain the motion of a thrown ball or a rainbow without QM. Every scientific model has elements that just have to be accepted, even QM.
JohnMnemonic Posted February 27, 2018 Posted February 27, 2018 (edited) Quote So QM cannot explain magnetism after all. I think, that there's still no part of physics, which would explain magnetism... Quote My example of the deflecting beam was poorly worded. I was referring to the mechanical deformation of a structure. QM doesn't deal with mechanics of solid objects. To use QM in such case, you would have to describe the behavior of all the particles, which create a macroscale object. It might be possible - but I won't even try... Quote My point is: I can explain the working of EM devices perfectly without QM, just like I can explain the motion of a thrown ball or a rainbow without QM. Hmm, then explain me, how works a pernament magnet, without using QM. Rainbow can't be explined without QM - as you need to describe the frequencies of visible light (photons). Light/photons is an EM radiation and this is pure QM... Quote . Every scientific model has elements that just have to be accepted, even QM. Of course. QM is confirmed by experiments and observations. It works - although no one actually knows why and how it works... Edited February 27, 2018 by JohnMnemonic
Strange Posted February 27, 2018 Posted February 27, 2018 5 hours ago, JohnMnemonic said: If you want to understand electromagnetism you HAVE to deal with QM - sorry, but there's no other way... It depends what level you want to understand it. Classical theory is perfectly good enough for most everyday cases. 3 hours ago, JohnMnemonic said: Actually, there's no explanation, why subatomic particles have any properties at all - magnetic moment, electric charge or mass. That is not really the role of physics. Physics describes how things with those properties behave. (It is possible that some future theory might explain why some of those properties exist, but there will be other unexplained things.)
swansont Posted February 27, 2018 Posted February 27, 2018 5 hours ago, JohnMnemonic said: I think, that there's still no part of physics, which would explain magnetism... The Lorentz transform of the electric field. 5 hours ago, JohnMnemonic said: Rainbow can't be explined without QM - as you need to describe the frequencies of visible light (photons). Light/photons is an EM radiation and this is pure QM... Then this depends on your definition of explain. That light has different wavelengths and frequencies is observed. Why this is the case may require QM, but that is not a prerequisite for explaining refraction and reflection, which can be done classically. 5 hours ago, JohnMnemonic said: Of course. QM is confirmed by experiments and observations. It works - although no one actually knows why and how it works... The "why" is not part of the science, though, so this lack of knowledge is not a failing of the science.
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