# Questions tagged [magnetic-fields]

For questions that utilize the concept of magnetic fields (commonly denoted by the letter B), or for questions whose answers likely involve magnetic fields. More specific than the [tag:magnetism], as questions about the phenomenon & theory of magnetism do not necessarily involve the discussion of fields.

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### Average force between two parallel finite wires with AC

Imagine 2 parallel antennas (wires) of equal length (a) with a distance r between them. Both have AC currents with identical sine wave forms (equal frequencies and amplitudes) . They are also in-...
777 views

### Sequential Stern-Gerlach devices - realizable experiment or teaching aid?

At least one textbook  uses sequential Stern-Gerlach devices to introduce to students that the components of angular momentum are incompatible observables. Viz., the $z$-up beam from a SG device ...
807 views

### Could the Faraday's rotating wire experiment be explained without using Lorentz force?

I read Faraday's rotating wire experiment which resulted in the invention of the homopolar motor. He was clever enough to think it that way and make the wire rotate around one of the poles of the ...
238 views

### What is actually happening when a magnetoresistive magnetometer degausses itself?

I'm trying to understand if anisotropic magnetoresistive devices themselves (not other passive ferromagnetic components) can become magnetized, and if so, how the application of a DC 1.1 gauss field ...
1k views

### Biot-Savart law from Ampère's with multivariate calculus

Let us assume the validity of Ampère's circuital law $$\oint_{\gamma}\mathbf{B}\cdot d\mathbf{x}=\mu_0 I_{\text{linked}}$$where $\mathbf{B}$ is the magnetic field, $\gamma$ a closed path linking the ...
607 views

### Boundary conditions on current carrying wire

I'm trying to simulate by finite elements method Maxwell equations for a current carrying wire. My 3d geometry consists of a cylinder and a box containing it. I will use a mixed formulation and ...
907 views

A long cylinder of radius $R$ is made from two different material. Its radius $r<r_0$ $(r_0<R)$ part is a material with superconducting transition temperature $T_1$, and its $r_0<r<R$ ...
212 views

### 2 Particles in a Landau level interacting via a Central Potential

I am studying Robert Laughlin's paper about the Franctional Quantum Hall Effect http://gtwlx.jpkc.fudan.edu.cn/reference/FQHE-T.pdf . In it, while he is setting up his motivation for the Laughlin ...
745 views

### Current geometry and Ampere's law

Under the right circumstances, Ampere's law $\oint \vec H\cdot d\vec \ell=I_{encl}$ can be used to deduce the field $\vec H$ at a point from the current enclosed by the circuit which produces $\vec H$....
945 views

### How to calculate the energy transfer between working coil and working piece and dissipated energy of working piece in induction heating?

For who don't know how does induction heating work, a short description can be found here. However, my question is about physics. Assume I have a coil inductor calculated carefully 50 uH as below: ...
6k views

### How to calculate the magnetic dipole moment of a bar magnet?

I want to calculate the force between two magnets. In a previous Phys.SE question, I was told that I needed to use the dipole-dipole interaction, but that equation depends on $m$, the magnetic dipole ...
12k views

### Force from solenoid

I'd like to approximate the force from a solenoid, or at the very least find a formula which is proportional to the force so that I can experimentally find the constant for my particular case. ...
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### Why does type-I superconductor behave differently than type-II as $H$ is increased?

As one increases the external magnetic field $H$ above a critical value $H_c$, a type-I superconductor abruptly changes to a normal conductor. But for type-II, the transition is not sharp but gradual ...
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### Why a superconductor expel magnetic lines of force from inside completely when cooled below critical temperature?

Suppose a superconductor which is in a normal state (i.e. $T>Tc$) is subjected to a magnetic field. As soon as magnetic field switched from 0 to some value, eddy currents will develop on the ...
325 views

### Is it possible to create arbitrary shapes of magnetic fields?

I've been reading about Transcranial Magnetic Stimulation (TMS) which can activate neurons using a magnetic field, which got me thinking... what if we can pick and choose exactly which neurons to ...
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### How to store magnets?

I have two identical powerful disk-like magnets (with hole in the center). They have same size. They are stuck together (attract). I have a bunch of sphere magnets. I left them "collide" and form a ...
82 views

### flux threading through superconducting ring

I have been confused over the wording used in this paper describing RSFQ logic circuits: http://www.mukhanov.com/uploads/LikharevSemenov-RSFQReview_IEEETAS91.pdf From page 6: " If such a single flux ...
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### Why can't we take a current carrying bar to determine the magnetic field in Biot savart law?

Our teacher told us that to determine the magnetic field by Biot savart law, we should always consider a wire and not a bar. I don't get the reason for the same. Is it because then we have to take in ...
89 views

### Lighting an Electric Bulb with Earth's Magnetic Field

Yesterday, I was solving some problems of Electromagnetic Induction. Suddenly a thought struck my mind. Earth has its own magnetic Field.If an aircraft of metallic body is flying in the air then ...
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### Why do paramagnetic materials require large fields to achieve magnetic saturation?

I'm performing an experiment on a paramagnetic sample, and the field strengths we are applying range from -7T to 7T, which are impressively large field magnitudes. However, we still are not observing ...
246 views

### What causes diamagnetism?

What makes a diamagnetic substance repel a magnet? If one explains it on the basis of cancelation of dipole moments in an atom and Lenz's law, shouldn't the diamagnetic substance be attracted to the ...
63 views

### What are the relations between a ladder algebra and an $SU(2)$ algebra?

I am studying elementary models of the Quantum Hall Effect. I don't have a strong background in Lie algebras so I was hoping someone could elaborate on the following observation: For a free particle ...
67 views

### How to write integral to calculate the area where a field is between two limits?

I would like to express the following quantity in a mathematical form, but cannot think how I would write the integral. "The area on the surface of a cylinder where the magnetic field is between two ...
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### Enhancing strength of magnet, practical question

I feel like I'm shooting a squirrel with a howitzer asking my question on the physics stack exchange, but here goes... I have a long ring-shaped (1cm outer dia x 3cm length) rare earth magnet that I ...