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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70
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9answers
13k views

How can magnets be used to pick up pieces of metal when the force from a magnetic field does no work?

I learned that the force from a magnetic field does no work. However I was wondering how magnets can be used to pick up pieces of metal like small paperclips and stuff. I also was wondering how ...
34
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6answers
12k views

Does a magnetic field do work on an intrinsic magnetic dipole?

When you release a magnetic dipole in a nonuniform magnetic field, it will accelerate. I understand that for current loops (and other such macroscopic objects) the magnetic moment comes from moving ...
26
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4answers
6k views

What is the magnetic field inside hollow ball of magnets?

Setup: we have a large number of thin magnets shaped such that we can place them side by side and eventually form a hollow ball. The ball we construct will have the north poles of all of the magnets ...
35
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2answers
16k views

Does special relativity make magnetic fields irrelevant?

I've heard that special relativity makes the concept of magnetic fields irrelevant, replacing them with relativistic effects between charges moving in different velocity frames. Is this true? If so, ...
25
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2answers
15k views

What prevents this magnetic perpetuum mobile from working?

As a child, I imagined this device, which may seem to rotate indefinitely. I have two questions. Is this perpetual motion machine already known? If it is, could you please give some references? What ...
9
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3answers
20k views

Do magnets lose their magnetism?

I recently bought some buckyballs, considered to be the world's best selling desk toy. Essentially, they are little, spherical magnets that can form interesting shapes when a bunch of them are used ...
39
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5answers
23k views

Is Biot-Savart law obtained empirically or can it be derived?

There's already a question like this here so that my question could be considered duplicate, but I'll try to make my point clear that this is a different question. Is there a way to derive Biot-...
37
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6answers
94k views

Can someone please explain magnetic vs electric fields?

I've looked through about 20 different explanations, from the most basic to the most complex, and yet I still don't understand this basic concept. Perhaps someone can help me. I don't understand the ...
3
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1answer
2k views

How does a magnet work?

I'm having trouble understanding how a magnet (not the field that is generated as a result but the material itself) work. The particles are aligned in a specific direction to give rise to force but I ...
-1
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1answer
769 views

What is the nature of the magnetic fields? [closed]

In this question, I am hoping to find out if there is an explanation to the magnetic hidden forces. In other words, what causes these fields? Is there any suggested theory, or any confirmed ones ? ...
3
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3answers
18k views

Manganese has more unpaired electrons than Iron so why is Iron ferromagnetic Manganese paramagnetic?

Manganese has five unpaired electrons, but Iron has four, then why is Iron ferromagnetic and Manganese paramagnetic? What's that property I'm missing?
18
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6answers
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Can magnetic fields be redirected and focused at one point?

I know that magnetic fields can be redirected, but... given a situation where you have static magnetic field over a large area, and you want to quickly change the magnetic field strength. Is it ...
12
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2answers
2k views

What is the mechanism by which magnetic fields do work?

I've seen some conflicted answers to this question in texts and on the web, in the case of a dipole, for example. Do magnetic fields do work directly, or is it their induced electric fields that do ...
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5answers
38k views

How long does a permanent magnet remain a magnet?

I have a bunch of magnets (one of those game-board thingies) given to me when I was a school-going lad over 20 years ago, and the magnets feel just as strong as it was the day it was given. As a ...
17
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8answers
10k views

What is the electric field generated by a spinning magnet?

Consider a cylinder of permanently magnetized material, with uniform magnetization pointing along the cylindrical symmetry axis (the $z$-direction). The magnet is rotating about its cylindrical ...
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1answer
237 views

Eddy current induce EMF

Q1 Suppose there is a wire having AC current so as ac current is alternating it creates back EMF whether that back emf produces current? If yes then that current is same as eddy current or not? And ...
2
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2answers
3k 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 ...
4
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4answers
1k views

How any material can provide electrostatic and magnetic shielding

Several metallic objects like Iron, Copper etc can provide electrostatic shielding (one should remain inside the car during thunderstorm) and several superconductors like HTS (High Temperature ...
4
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3answers
4k views

Can current be induced in a superconductor?

Moving a magnet close to a conductor induces a current. If it consists of a superconducting material with resistance $R=0$, then my textbook says: Then the induced current will continue to flow ...
3
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1answer
3k views

Why magnetic flux density is material dependent where as electric flux density is not?

Electric flux out of a closed surface depends only on the charge enclosed. So, intuitively, the number of flux lines crossing unit area is constant regardless of the material. However, the number of ...
16
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2answers
46k views

What is the difference between an electric and a magnetic field? [closed]

This question is a consequence of another question of mine which is about spin. Here is my spin question. What is the difference between these two fields? How do they occur? Am I right if I say that ...
11
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2answers
11k views

Is magnetic force non-conservative? [duplicate]

If magnetic field is conservative, then why not the magnetic force? My professor thinks it is non conservative but he couldn't explain to me why?
14
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3answers
27k views

How does Hendo hoverboards achieve the self-propelling motion? What is the MFA?

From what I understand of the idea behind Hendo hoverboards, they use four disc shaped hover-engines to generate a self-propelling motion. I also understand that it uses Lenz's law and eddy currents. ...
15
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4answers
8k views

Why should Conservative forces have their curl equal to zero?(intuition)

There are several conditions that must be met in order for a force to be conservative. One of them is that the curl of that force must be equal to zero? What is the physical intuition behind this? If ...
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2answers
2k views

Mechanism by which electric and magnetic fields interrelate

I read that force due to electric field on some particle in one reference frame can exhibit itself as force due to magnetic field in some other reference frame and that electric and magnetic fields ...
6
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2answers
7k views

Magnetic field lines

When I searched the net about magnetic field lines, Wikipedia told something about contour lines and that magnetic materials placed along a magnetic field has some specific loci, which i did not ...
9
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4answers
10k views

Is there any example where electric and magnetic fields are not perpendicular?

Perpendicular electric and magnetic field creates light or other electromagnetic waves. Is it a necessary property to have a perpendicular fields? If not what would happen when the fields are not ...
3
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1answer
996 views

Induced magnetic field produces electric field and vice versa forever!

So here are the two of Maxwell's laws that I am interested in: So we have the simple circuit (from google): So, before the system goes into steady-state we know that charge slowly accumulates on the ...
23
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6answers
28k views

Where do magnets get the energy to repel?

If I separate two magnets whose opposite poles are facing, I am adding energy. If I let go of the magnets, then presumably the energy that I added is used to move the magnets together again. However, ...
11
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4answers
9k views

How do permanent magnets manage to focus field on one side?

The actuator of a hard drive head consists of two very strong neodymium magnets, with an electromagnetic coil between them. If you take that apart, the magnets attract each other very strongly. There'...
6
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3answers
16k views

Why does an electric motor burn up when you physically stop it?

As an electric motor spins, the energy from the electricity is 'conducted' to the rotor by the magnetic fields. However, when the motor is stopped, the energy becomes heat and burns up to motor. ...
5
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1answer
594 views

Physical interpretation of 2-forms dual to pseudovectors

Mathematically for every 3D pseudovector $x^i$ there is a 2-form $F_{ij}=\epsilon_{ijk}x^k$ such that the 2-form transforms properly under all orthogonal transformations. Therefore I would expect it ...
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1answer
621 views

How does the electrons' magnetic dipole moment get influenced when electrons are moving through a magnetic field?

How does the electrons' magnetic dipole moment get influenced when electrons are moving through a magnetic field? How does the electrons' intrinsic spin influence the direction of the electrons' ...
4
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1answer
556 views

What are magnetic field lines?

Does a magnetic field have concentrations of magnetic force lines as seen when putting iron filings over top a bar magnet or are these imaginary? I.e. are they just an artifact of the iron being a '...
3
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1answer
16k views

From where do the permanent magnets get energy from? [duplicate]

I have a doubt about permanent magnets. If a magnet is permanent it can attract some materials permanently. Attracting something involves energy. If a permanent magnet can do this forever, from where ...
3
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4answers
969 views

Positive work by a magnetic field

Consider a single charge moving only under the influence of Magnetic Field $\vec{B}$. The charged particle moves in a circle and the work done by $\vec{B}$ is 0. Now consider a current element in a ...
2
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1answer
140 views

Geomagnetic reversal?

I have always been told that the geomagnetic field acts "as if" there were a bar magnet inside the Earth. I now this is not true, but I feel that knowing what is actually going on would help me ...
0
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1answer
324 views

Are magnetic fields just modified relativistic electric fields?

Feynman's Lectures, Volume 2, says that the electromagnetic force is invariant in any reference frame, and the magnetic force in one frame becomes the electric field in another. And Wikipedia says: ...
7
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1answer
7k views

Why is the geomagnetic north pole at a different location from the magnetic north pole?

According to this site Magnetic North, Geomagnetic and Magnetic Poles The Geomagnetic poles (dipole poles) are the intersections of the Earth's surface and the axis of a bar magnet hypothetically ...
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2answers
1k views

Why is the B field of a solenoid equal to $\mu_0 i n$ while that of a loop is $\frac{\mu_0 i R^2}{2(R^2+z^2)^{3/2}}$?

In the B field of the loop, if R is the radius and z is the distance along the axis perpendicular to the center of the loop, let z go to zero, and multiply by N loops. Starting with the B field of the ...
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3answers
1k views

Why do we multiply the magnetic flux by the winding number?

A current I flows through a solenoid (with n turns). Self inductance is $L$. If the magnetic flux is $\phi$, I am taught that $-n\phi=LI$ I dont understand the part with $n$, why do we have multiply ...
0
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1answer
536 views

Magnetic Shielding?

Can magnetic fields be "blocked"? For example, in the game, TitanFall, a robot stop bullets with ( presumably ) a magnetic shield. I wish to calculate the magnetic force required to stop a bullet ...
22
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5answers
49k views

What are the fields produced around a current carrying conductor?

If you consider a current carrying conductor, every instant an electron enters the conductor, another electron will be leaving the conductor. Thus, the current carrying conductor will not be charged (...
33
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2answers
4k views

Why does the Earth even have a magnetic field? [closed]

From my knowledge of magnetism, if a magnet is heated to a certain temperature, it loses its ability to generate a magnetic field. If this is indeed the case, then why does the Earth's core, which is ...
28
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5answers
3k views

Why do we deal only with large scale magnetic fields in astrophysics, and not electric fields?

In astrophysics there is a lot going on about strong, large scale magnetic fields: in stars (prominences), magnetic dynamos, compact accretors collimating jets, etc. There's even a special ...
14
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2answers
8k views

Why are magnetic fields so much weaker than electric?

In EM radiation, the magnetic field is $ 3*10^8$ times smaller than the electric field, but is it valid to say it's "weaker". These fields have different units, so I don't think you can compare them, ...
5
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3answers
1k views

The magnetic field of a magnetic monopole

Let us define the magnetic field $$\vec{B} = g\frac{\vec{r}}{r^3}$$ for some constant $g$. How can we show that the divergence of this field correspond to the charge distribution of a single magnetic ...
10
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2answers
23k views

Why is the divergence of a magnetic field equal to zero?

We know due to Maxwell's equations that: $$\vec{\nabla} \cdot \vec{B}=0$$ But if we get far from the magnetic field, shouldn't it be weaker? Shouldn't the divergence of the field be positive? If ...
9
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4answers
3k views

Elementary Particle of Magnetic Field

If gravity - a field force - has an elementary particle, the graviton, why don't other field forces like magnetic fields have their elementary particles? I mean, why isn't there a magneton? Or, what ...
7
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2answers
2k views

Which mathematical operation does the right hand rule for current come from?

I am currently wondering about the famous right-hand rule for magnetic fields around currents. Where does it come from mathematically that when you point with your thumb in the direction of the ...