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 ...

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Force Exerting on a magnetic train

A question is already asked ( How does this “simple” electric train work? ). But I've got a question about it. In order to calculate the force which is being exerted on the system including magnets ...
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1answer
27 views

Where does the earths magnetic field originate [duplicate]

To my knowledge my knowledge magnetism comes either from an electric current flowing through an object or from a permanent magnet which can be created by heating certain ferrous metals to specific ...
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1k views

Generating unlimited electricity through magnets

Well i had seen a toy, which i till date don't know was it battery powered or not? and also could it be used to actually create energy (I know that it is not possible but whats the problem?) ...
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1answer
5k views

How do 2 magnets spin by themselves if positioned precisely?

A few years ago I went to a museum, where there was a board with 2 bar magnets, on a pole each so they could rotate. If you rotated them so the lined up with the same poles (N) facing each other, ...
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4answers
302 views

Do magnets redshift light?

Do magnets redshift light? Suppose we have an extremely powerful magnet (say the size of the Sun) and we have a smaller paramagnetic material above it (say. Titanium Brick which is ...
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2answers
60 views

How virtual photons give rise to electric and/or magnetic field? [duplicate]

Say a neutron which have magnetic moment despite carrying no charge. Isn't both the electric field and magnetic field consist of virtual photons? So how can the same virtual photons give rise to 2 ...
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1answer
36 views

Analogue of charge for magnetic fields?

Now, I understand how there are no magnetic monopoles, and hence no analogue of magnetic charge in terms of a scalar field, but is there a similar concept that instead uses a vector or spinor field to ...
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1answer
122 views

Find magnetic field in a solenoid for different regions?

A steady current I flows along an infinitely long hollow cylindrical conductor of radius R. This cylinder is placed coaxially inside an infinite solenoid of radius 2R. The solenoid has n turns per ...
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2answers
265 views

Magnet dimensions for 3-phase permanent generator

I'm making a 3-phase permenant generator. According to Faraday's law, the emf produced is negative number of turns times the change in magnetic flux over the change in time. If it is only the CHANGE ...
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Do metal shavings affect the magnetic field they are used to visualize?

It's obvious that the use of metal shavings to visualize magnetic field lines was instrumental in Faraday's work to develop electromagnetic theory. But they also did too good a job of convincing ...
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2answers
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Why magnetic field lines and force are not orthogonal with magnets?

The below explanation why magnetism exists is superb in this video. The explanation about magnets is also great in this video. A magnet has atoms with unpaired electrons forming mini magnets. The ...
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23 views

Magnetic Forces and Junkyard Magnets: What's Going On? [duplicate]

In my electromagnetic theory class, I learned that magnetic forces do no work. This is easy to see when observing a cyclotron; the speed never changes, so the kinetic energy never changes and ...
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1answer
241 views

Induced Current & Lenz's Law - 2 Circular Loops with same direction of current

I'm new to the wonderful world of physics, and I'm really confused about magnetism and induced currents. Let's say we have 2 circular closed loops that each carry a current $I$ clockwise and the ...
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1answer
20 views

Computing magnetic fields contours

I have a set of Velcro-backed magnets of varying strengths that I can stick to a sheet of non-magnetic material. What are the standard techniques for computing the magnetic field lines for an ...
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1answer
664 views

Can we increase the magnetic flux for a permanent magnet?

When we pass current to the permanent magnet does its magnetic flux, magnetic property of attraction and repulsion increases? if possible Is there any other way for increasing the magnetic flux?
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2answers
59 views

Why bar magnet can produce magnetic field?

Say I wrapped a piece of wire around an iron bar in a closed circuit connected to a DC power supply, the electrons starts flowing and moving charge produce magnetic field. Yet a bar magnet can produce ...
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3answers
2k views

Can an electromagnet repel a strong magnet?

When the direction of current is reversed, the polarity of an electromagnet should be reversed. I am trying to understand why this did not happen in an experiment I conducted today. An electromagnet ...
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1answer
21 views

What is phase coherence?

What is phase coherence? I have exam next week in MRI, and I can't understand this sentence: Time T2 relates to loss of resonance and thus the loss of transversal magnetization. This occurs due ...
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1answer
111 views

How to calculate earth's magnetic field by time period of suspended magnet?

Assuming that torsion of the suspension wire small enough to be neglected, how can we derive earth's magnetic field by measuring time period of an oscillating magnet suspended on a string?
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How does the magnetic current in a MRI machine flow? [closed]

For a project, I was researching about the MRI machine, and I need to find how the electric current in a MRI machine flows.(like which direction, what shape, and how) I have tried google and wiki, but ...
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1answer
546 views

How does temperature affect magnets?

How does an increase/decrease in temperature affect: Strength of the magnet Polarity Other changes? I have made some research and I have found that increasing the temperature turns ferromagnetic ...
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2answers
115 views

Could I make a magnetic foam or film by mixing magnetic dust?

I'm a developer and tinkerer more than an academic, and I'm not sure if this question, being more practical and less theoretical, will be welcome or not here. But here goes, with apologies in advance ...
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2answers
253 views

Are magnetic orbits possible?

I have a small ball with lots of magnets embedded in it with all the north poles facing out and I have a big sphere with lots magnets embeded in it with all the south poles facing out. I set the ...
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3answers
5k views

Non-conservative electric fields due to changing magnetic flux?

What I read in several places, tells me that, the fact Coulomb's Law follows inverse-square law and gives a force which is radial, implies that a static electric field must be conservative.(In short, ...
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2answers
441 views

Repelling a weak permanent magnet with an electromagnet

I have a question about magnetic repulsion. Suppose I have a permanent magnet (axially magnetized) placed on top of the iron core of an electromagnet. I want to switch on the elctromagnet to repel the ...
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1answer
57 views

Flux cutting in a uniform magnetic field

Say we have a uniform magnetic field acting into the page, and we have a bicycle wheel which is spinning at a constant tangential velocity $v$. Each spoke has a equal length, $l$. Reading has told me ...
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1answer
3k views

Magnetic field inside finite solenoid

In my book they don't really derive the equation of the magnetic field inside of a finite solenoid. They just give me equation 1 and image and the end result, equation 2. ...
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1answer
452 views

Coercivity of a ferromagnetic material?

I understand that coercivity is the field/force required to demagnetize/magnetize a ferromagnetic material. What if we had two opposite magnetic fields of different strengths values H acting on the ...
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2answers
2k views

Is it possible to levitate a toy maglev train using only permanent magnets as long as the train stays in motion?

I am fascinated with magnets, and specifically the idea of magnetic levitation. I recently purchased a Levitron toy maglev train and have enjoyed finding the perfect sweet spot at which it levitates, ...
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0answers
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Can I emit light from an inductor? [duplicate]

As I understand it, inductors create a magnetic field when current flows through them, and light is an electromagnetic radiation. So, is it possible for an inductor to generate magnetic waves of the ...
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1answer
34 views

Conservation of Angular Momentum in Einstein - de Haas effect

I am not really sure why the law of conservation of angular momentum should hold true in the Einstein - de Haas effect. Consider the following excerpt about the phenomenon (taken from Magnetism in ...
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1answer
3k views

Why is the magnetic field stronger at the edges of a bar magnet?

I have been performing an experiment at school in which I test the force on an iron surface from the magnetic field of an electromagnet. The electromagnet has a rectangular iron core. The theory ...
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1answer
435 views

Question about superconductivity

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 $r_0<r<R$ ...
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1answer
103 views

What happens if a current flows through a wire wrapped around a magnetised material?

A cylinder of radius $a$ has a uniform magnetisation along its axis, which results in zero bound volume current density and a bound surface current density $M\hat{\phi}$. A coil with $N$ turns and ...
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0answers
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The frequency induced by the alternating current

Let set up the experiment as followed. A string is stretched at two ends. Two magnet poles N and S are placed under and above the string. Now we let an alternating current go through the string with ...
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2answers
147 views

Why in electrostatics is $dV=-E.dr$ but in electromagnetic induction, $EMF=+E.dS$?

In electrostatics we learned that $$dV=-E.dr$$. I understood the derivation which was used to derive this. Now when I have come to Electromagnetic Induction,I see that when there is a time varying ...
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0answers
28 views

Magnetic field of a permanent magnet - numerical calculation

I'd like to understand methods for calculating the magnetic field generated by a magnetized piece of material, e.g. a permanent magnet. I was wondering about the approach described here as it seems ...
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1answer
645 views

Forces on a wire moving in a magnetic field?

When a wire is placed inside a magnetic field and current starts to flow in that wire, that wire experiences the Lorentz force = $IL \times B$ and beings to move. Aside from induced motional - ...
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1answer
563 views

Peierls substitution vs minimal coupling

In the presence of vector potential (let's assume it's uniform), a tight-binding Hamiltonian will be changed according to the Peierls substitution: $$t_{ij}c_i^{\dagger}c_j \to ...
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1answer
746 views

Do intergalactic magnetic fields imply an Open Universe?

According to a paper on the arXiv (now published in Phys Rev D), they do. How credible is this result? The abstract says: The detection of magnetic fields at high redshifts, and in empty ...
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1answer
30 views

Shift in pixels between 2 tissues in MRI

I have the following question: given a known chemical shift $\delta$ between 2 tissue proton resonances and a MR image sequence with a total spin-echo sampling time of $t$ ms, what is the spatial ...
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1answer
114 views

Prove that Laughlin's 3-electron states are a complete set of states

In R. B. Laughlin's 1983 Physical Review B article, Quantized motion of three two-dimensional electrons in a strong magnetic field, Laughlin separates out the center of mass motion of the electrons, ...
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1answer
35 views

Auxiliary magnetic field identically zero?

Consider a 3D space that's filled up completely with a material of fixed magnetization $\mathbf{M}$ (i.e. everywhere in space the magnetization points in the same direction and has the same ...
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0answers
32 views

Electric field due to a current carrying loop

I want to know how I can calculate the radiated electric field in the far zone of the loop. Knowing that the loop is in center at the origin of a x-y plane Knowing that the loop as a time-harmonic ...
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0answers
45 views

Can a magnetic field weaken aluminum?

I'm wondering if there is any reason to suspect that applying a magnetic field to a piece of solid aluminum would weaken it structurally in any way. The application is that I would like to put a stir ...
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1answer
27 views

Difference between flux of wire loop and wire in a uniform magnetic field

How come when a wire loop sweeps out an area in a uniform magnetic field and moves with constant velocity there is no induced current because there is no change in flux. However, when a straight wire ...
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2answers
542 views

Magnetic field and Newton's third law

If a magnet exerts force on a iron block (opposite and EQUAL), does a iron block also exerts force on magnet (via Newton's third law)? If yes then what magnetic property does it has to produce equal ...
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3answers
207 views

Do moving charges get affected by the magnetic field they create while moving to constitute current? If not, how can self-induction be possible?

Let a bunch of charge move with a constant velocity $\mathbf v\;.$ Since, the charges are moving, they would create magnetic field $\bf B$ as it is current that produces magnetic field. Now, would ...
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1answer
297 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 ...
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1answer
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How does this approximation of the $B$-field of a charged rotating disk for $z\gg R$ make sense?

Consider a disk of radius $R$ rotating with angular velocity $\omega$ and with a surface charge density $\sigma$. I have shown that the magnetic field as a function of the distance along its axis (z) ...