# Tag Info

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TL,DR: Magnetic coupling results in lower transmission of sound energy than physical contact Controlling what surfaces vibrate gives more control over sound generation The same benefit could be achieved with other forms of isolation (e.g. foam) but it wouldn't look as cool. It is bunk, mostly. A magnetically levitating speaker maintains a ...

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This advertising strategy is basically using pseudoscience to get naive people to buy a product. The efficiency problem in speaker design has nothing to do with momentum transfer from the speaker to the air. That's trivial, since the mass of air a speaker moves is typically orders of magnitude less than the mass of the speaker itself. Instead, the (low ...

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I think that the problem is that you are considering an electric current at distance $r=0$ with the Biot-Savart formula. It's like when you have a wire with a current and you want to find magnetic field on the wire, or electric field on a point-like charge. In your problem current $J$ is a linear function of distance, but in Biot-Savart you have something ...

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Increasing the number of turns increases the magnetic field if the current remains constant. In your situation, you are postulating (implicitly) that the applied voltage is constant, and that the current is reduced. The product $N\cdot I$ is therefore unchanged, and the magnetic field does not increase when you increase the number of turns of a resistive ...

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Nope! The first two large magnets in 1) have nonzero dipole moments, while in 2), the pairs of magnets have the magnetic dipole charge canceled. The right way to divide the large magnet with "S" at the top and "N" at the bottom is clearly to have two magnets with "S" at the top and "N" at the bottom! It doesn't matter whether these two half-magnets mutually ...

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I believe that for an ordinary conductor, there is nothing special for a static magnetic field. But this relates only to the electrical properties of that conductor - many material have some magnetic properties as week, and those would of course modify the B field. But for the purpose of this question the B field follows the dipole field "in free space" - no ...

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There is an electric field due to the changing magnetic field, which has direction left -> right. Due to this field, there is an immediate charge seperation caused in the metal rod (-ve near M and +ve near N) which creates another electric field of equal magnitude and opposite direction to perfectly cancel the external electric field. Thus the net electric ...

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What explains this "channeling" behavior of ferromagnetic materials? In other words, is this explainable using the normal methods for magnetic field calculations such as Biot-Savart and treating the ferromagnet as consisting of infinitesimal dipoles Ferromagnetism is a quantum phenomenon, but yes, it can be treated classically as a volume of dipoles ...

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See Appendix B on page 47 and further of this article: Note that the failure of the “rest mass” m to be constant resolves a paradox concerning what one is taught in elementary physics courses: On one hand, one is (correctly) taught that an external magnetic ﬁeld can “do no work” on a body, so a body moving in an external magnetic ﬁeld cannot gain ...

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I doubt my description can be improved other than with a picture. Now the interesting thing here is that I do not know which way the current is flowing, because I do not know which way the compass needles are colour-coded. I guess that the red represents the north pole. I do know that if the current flow is reversed then the needles will swap direction. ...

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The field from a current in a wire is purely magnetic for a static current. When the current varies with time, there will be radiation. What you are missing is that a radio antenna doesn't operate with DC. You can perhaps understand it like this: the magnetic field from a current loop depends on its magnetic moment, which is current times area. When the ...

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The magnetic interaction among the electrons is very weak. The electrostatic interaction among the electrons lead to Hund's coupling among the electrons which in turn results in magnetic arrangement of these tiny magnets and magnetism of the whole solid.

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Well, the details are important. From the abstract in your link of the paper we see that: 1) it is a publication from 1978 2) it calculates rates for positronium annihilation in the very high magnetic fields found in astrophysical situations, 10^12 Gauss It explicitly states that the momentum contribution comes from the magnetic field. In the relevant ...

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First consider Faraday's law, which states that $$\nabla \times \textbf{E} = -\frac{\partial \textbf{B}}{\partial t}.$$ We can interpret this as follows: whenever we are generating a magnetic field that changes with time, there is an associated electric field, and vice-versa. An equivalent interpretation is that a changing magnetic field causes a ...

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