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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2
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3answers
112 views

Why can the divergence of vector potential be anything?

Purcell in his book was deriving the vector potential $\bf A$ using $\text{curl}\;(\text{curl}\; \mathbf A)= \mu_0 \mathbf J\; .$ After some algebra, he came to this: $$-\frac{\partial^2 A_x}{\...
0
votes
4answers
152 views

Why does the frequency of a Transformer not change?

I was reading about the transformer, when I came across a note by the author that stated that the Frequency is not changed as the flux linked to the secondary coil in a transformer changes. Is there ...
0
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0answers
14 views

Books about non-uniform magnetisation

I need to study non-uniform magnetisation and the only book where I found this was Berkeley Physics Course Vol.2. Is there other book's options to this issue?
2
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3answers
148 views

Has this double slit experiment been performed with electrons?

I don't know if we have the technology yet. Double slits, one electron at a time. The moving electron should produce a magnetic field. Can we detect such a weak magnetic field and tell which slit ...
0
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0answers
73 views

Magnetic hysteresis energy loss derivation

we have that the magnetic energy stored in a field is : $$W_m = \frac{1}{2}\int_v B.H dv$$ From here im unsure how to get to the expression that the power dissapated in a hysteretic cycle is given by ...
1
vote
1answer
22 views

how is current measured through ammeter? [duplicate]

If we join a shunt through a galvanometer,it makes an ammeter.but in parallel arrangement voltage is same and only some amount of current is passed and not the total current of circuit.so how does the ...
0
votes
1answer
249 views

Is the number of turns in a loop part of the magnetic flux?

In all both my physics textbooks, the number of loops $N$ is left out of the equation for magnetic flux $\phi_B = \int_s \vec B \cdotp\hat n dA$ and only when calculating the Emf induced by an ...
0
votes
1answer
15 views

Local nuclear magnetic field compared to macroscopic field

In an NMR experiment, I the local magnetic flux density of an iron sample was found to be roughly 33 T, by checking for a resonance frequency of the magnetic dipoles. How can it be that such a high ...
2
votes
0answers
44 views

What kind of cheap, available, magnetic metal could I use for my boardgame? [closed]

My question revolves around my need to snap plaster walls to plaster dungeon floors for a boardgame called Dungeons & Dragons. My intention is to glue and paint over metallic strips under the ...
1
vote
2answers
58 views

Is it possible to shield a magnetic field?

Is it actually possible to shield a magnetic field? They teach us at school that magnetic fields are generated by electricity running through the wires (that's how electromagnets work). On the other ...
0
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0answers
34 views

Redirectioning photons through magnetic lenses

What shape magnet/s would I need to create parallel lines from the ends of a rod shaped magnet?or what shape of magnet would create parallel lines? Is this close?
0
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0answers
19 views

Levi-cevita symbol, force on current by magnetic field of other current

I have the expression for F⃗1, the force on I1 due to the magnetic field of the current I2, using the Levi-Cevita symbol. However, one part of this double integral should equal zero mathematically or ...
0
votes
1answer
58 views

Does the alternating current “move” such that there can be Lorentz force present on the wire?

As in question, does the alternating current "move" such that there can be Lorentz force present the wire? Becuase the current alternates on a fixed place there can be no Lorentz force?
0
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1answer
51 views

Electric current through loop of wire

We have an electric current running through a wire loop, then we are interested in the magnetic field generated by this current (moving charges). The main question is, the value of the magnetic field ...
0
votes
2answers
124 views

Does the ring (in the picture) experience Lorentz force?

Does the ring in the picture below experience Lorentz force? Or should I say it's just some magnetic force? (Notice that the poles repel eachother.) I am unsure because of the setting with the ...
1
vote
1answer
33 views

magnetic force from v=0 and dB changing

magnetic force is defined as: $ \mathbf{F}=q \mathbf{v} \times \mathbf{B}$ so if v=0 there is no force. However Faraday's law states that if $d\mathbf{B}\neq0 $ then we have an induced emf even ...
0
votes
0answers
128 views

What makes the magnetic field inhomogeneous in the Stern–Gerlach experiment?

The magnetic field depicted in Stern–Gerlach experiment is described as inhomogeneous. Is that depiction the only depiction of inhomogeneous magnetic field used, or are there other examples of ...
6
votes
2answers
197 views

Is the thermal conductivity of metals affected by magnetic fields?

Especially for a ferromagnet a magnetic field should have a field-induced band shift in the density of states but I wonder if this shift is big enough to be significant and affect the thermal ...
0
votes
0answers
41 views

How does magnetic field gets generated by friction between high temperature molten metallic cores?

I was watching "Strip the cosmos" show on Discovery science channel last day and they explained that earth produces magnetic field due to rubbing of the two concentric cores, both the molten metal ...
0
votes
0answers
56 views

Is the saturation magnetization of a thin film different if you apply the field at different directions?

I'm getting different values of the saturation magnetization when I measure them in-plane versus out of plane. The saturation magnetization for the out of plane measurement is greater than in the in ...
1
vote
0answers
22 views

Why do magnetic forces scale down so poorly?

Im told by experts in MEMS and nanotech that magnetic forces scale down very poorly. This is one reason we have many MEMS devices based on electric forces/electrostatics but not on magnetics. Can ...
0
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0answers
51 views

A Magnetic Vortex in a Magnetic Vortex

This is not to scale. Can a magnetic vortex be compressed into a flat disk using magnetic entrapment? Can a magnetic vortex happen inside another magnetic vortex?
0
votes
2answers
77 views

Does radar affect magnetism?

Does radar affect magnetism? Let's say I have two magnets, one is suspending the other. Would radar affect the magnetic field?
0
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1answer
79 views

Finding the electric and magnetic fields from the vector potential $\vec A=\vec{E_0} e^{i(\vec k\cdot\vec r-\omega t)}$

I am trying to find the electric and magnetic fields from the vector potential $$\vec A=\vec{E_0} e^{i(\vec k\cdot\vec r-\omega t)},$$ I know $$\vec B=\vec \nabla\times \vec A$$ and $$\vec E=-\vec\...
-1
votes
1answer
184 views

Why does an electromagnet attract iron according to Special Relativity?

I saw a video of Veritasium on "How Special Relativity Makes Magnets Work" and came up with a question. So please watch the video first before answering my question as it is related to the video. 1) ...
1
vote
2answers
261 views

Direction of H and B inside and outside a bar magnet

I seem to have encountered a contradiction when thinking about the directions of $\textbf{H}$ and $\textbf{B}$ inside and outside a bar magnet. Suppose that a bar magnet has a roughly constant ...
0
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2answers
55 views

Hysteresis loss

It is know that ff an alternating magnetic field is applied to the material, its magnetization will trace out a loop called a hysteresis loop. The lack of retraceability of the magnetization curve is ...
3
votes
1answer
155 views

Which is more fundamental: $H$ or $B$? [closed]

According to Wikipedia, $B$ is called the Magnetic flux density / Magnetic induction / Magnetic field, while $H$ is called the Magnetic field intensity / Magnetic field strength / Magnetic field /...
0
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0answers
68 views

Distance of the electric field generated by a Slayer Exciter ( Variation of tesla coil )

I'm currently trying to create a really basic simulation of a slayer exciter for a demonstration I have to give at my college. The thing is we want to know how far does the electric field produced by ...
-1
votes
2answers
46 views

Magnetic field due to current, I don't get how you get the direction, can someone draw it for me? [closed]

Taken from here, 3rd problem. As you can see, no matter from which point current goes, from a to b or from b to a, in either cases, magnetic field would be down, right?
0
votes
1answer
110 views

How is magnetic field created in an atom according to quantum model

How is magnetic field created in an atom according to quantum model? I mean, we are taught about the magnetic field by bohr's model which assumes that electron revolves around the nucleus in a ...
0
votes
0answers
36 views

If I know how many atoms I have in a film, can I know the total magnetic moment?

Say I have a Co film and I know its volume so I know the total number of atoms in it. Using this plus the knowledge that each atom has a magnetic moment of 1.7 Bohr magnetons, would the total magnetic ...
1
vote
1answer
119 views

Why does transformer winding need large numbers of turns?

In transformers there are large number of turns in winding for both primary and secondary sides around the core. So, my question is why can not we just put one or two turns in winding as we need to ...
1
vote
2answers
63 views

Magnet and needle

When I place a needle near a clamped magnet and let it go, it moves towards the magnet. Since magnetic field cannot work on individual charge particles, we must conclude that the needle loses its ...
0
votes
1answer
71 views

A confusion with solenoidal windings

I have seen in solenoids, toroids, transformers, electromagnets and machines that the core is pretty insulated. Over this the winding coil is wrapped but it is a bare coil (turns are not insulated to ...
3
votes
0answers
53 views

Can a magnetic lock be negated or overcome by a stronger electro magnet? [closed]

Magnetic locks seem to be fairly standard on modern buildings. Is it, though, possible to negate a magnetic lock my placing an oppositely-polarized, strong electromagnet across from the magnets on the ...
1
vote
2answers
49 views

How does this incorrect model of a wire give the correct result for B-field produced?

I see in Griffith's book Introduction to Electrodynamics, 4th edition, the following model (paraphrased). Consider a wire (infinitely-long) with positive linear charge-density $\lambda$ moving to ...
-1
votes
3answers
77 views

development of magnetism in a magnet [closed]

If we cut a magnet, the magnetic field develops. But if we cut it vertically, then will the magnetic field develop?
4
votes
1answer
58 views

Why do these calculations of EM fields for a magnet and wire loop seem inconsistent?

Suppose you have a conducting circular wire loop and a magnet moving towards each other. They move along the $z$ direction with nonrelativistic constant speed $v$. Let the $B$ field of the magnet in ...
2
votes
1answer
72 views

Why a motionless proton doesn't feel any force in a magnetic field according to special relativity?

In this ( https://www.youtube.com/watch?v=1TKSfAkWWN0 ) specific video uploaded by Veritasium on YOUTUBE , we come to know about how special relativity makes magnets work. We observe that when a ...
40
votes
4answers
6k views

Is Earth really a magnet?

I am a student of class 9. When I was going through magnetism and read that an earth is a magnet I got some doubts. My question is: is earth really a magnet? Doesn anyone have any proof that earth is ...
2
votes
1answer
58 views

How to define a the outward direction of 4d simplex?

For a 2d simplex (triangle) with three vertices a,b,c, we could define the outward direction of the face as a-b-c, like define a magnetic field induced flux. For a 3d simplex (tetrahedron) with four ...
1
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0answers
53 views

When a coil makes a complete turn, why is does magnetic flux double with respect to time?

EMF, $\mathcal{E}$, is equal to -d($\phi$)/dt Where $\phi$ is magnetic flux. Why is it that if from $t_1$ to $t_2$ the coil makes a complete turn and during this turn the normal vector's angle with ...
3
votes
1answer
61 views

Entangled spins in a uniform magnetic field

I have been trying to calculate the time derivative of the expectation value of the operator representing the spin components of a a singlet state (e.g. sigma(z)tau(z)). I formed the tensor product of ...
22
votes
3answers
4k views

Extra strong magnet which doesn't demagnetize credit cards. How does it work?

I've just bought this case for my mobile phone. It has three credit card slots, which isn't strange at all, but in combination with a strong magnet closure, it almost seems a bit stupid, because, who ...
1
vote
1answer
52 views

Current carrying wire to suspend in midair? [closed]

A straight current carrying wire is inserted in a region of space where a strong magnetic field is directed vertically downward. How can the wire be oriented so that it is suspended in midair by the ...
0
votes
0answers
101 views

Current through moving bar on rails with non-constant magnetic field

I am working on the problem pictured below and I cannot figure it out. I have been using the equation d[flux]/dt = -BLv and V = -d[flux]/dt. However, since the magnetic field is not constant through ...
0
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0answers
61 views

How does mass of magnet with current-flowing wire inside change?

We just did an experiment where we put a coil inside of a magnet and let certain current run through the coil and measure the mass change of the magnet. I have looked/researched in textbook and ...
0
votes
2answers
298 views

Magnetic flux density of a solenoidal electromagnet

I am designing an electromagnet which will be used to test magnetic sensors. So I used to formula found at hyperphysics which relates the magnetic field flux density to the number of turns, the ...
6
votes
3answers
639 views

How to find the direction of an eddy current?

Suppose there is a magnetic field going from left to right. Suppose a thin sheet of metal conductor (e.g. a 1m*1m square) is dropped through the magnetic field such that the plane of the conductor is ...