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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5
votes
1answer
657 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 ...
5
votes
2answers
698 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 ...
2
votes
1answer
497 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 $r_0<r<R$ ...
-1
votes
0answers
26 views

Charged particle in rest frame and their magnetic field [on hold]

I’m wondering how statements like "A charged particle at rest creates an electric field, but no magnetic field" are right. An electron has an electric field and it has a magnetic dipole moment. Both ...
0
votes
0answers
8 views

Factors Effecting Neodymium Magnet's Grades and Strength?

Neodymium magnets have different grades in strength. Such as: N38, N45, N52... etc [ Where higher number means greater strength, in MGOe ] Since all magnets are made by saturating them in magnetic ...
2
votes
1answer
116 views

How force get transmitted when a magnet attracts iron?

According to particle physics , every fundamental force has its force carrier particle. Photon is a force carrier particle of electromagnetic force but how does force gets transmitted when a iron is ...
-3
votes
0answers
34 views

Pauli Spin Matrices [on hold]

i) Determine the effect of the pauli spin matrices $\sigma_x$ and $\sigma_y$ on the eigenstates of $\sigma_z$. Which physical process is conveyed on the eigenstates of $\sigma_z$ by applying ...
4
votes
0answers
27 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: ...
0
votes
0answers
19 views

How can magnets behave like springs? [on hold]

I have found this interesting video on the web, where thwy show how changing the geometry of a magnet can highly increase its strength, and produce different outcomes. At 5:47 the show how two ...
3
votes
1answer
135 views

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

At least one textbook [1] 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 ...
0
votes
0answers
32 views

Is my definition of a dipole and its dipole moment correct?

Assume that we have a dipole affected only by an applied magnetic field where only 2 possible orientations for its dipole moment are possible: "up" and down". A dipole is simply an object with a ...
0
votes
1answer
118 views

Magnetic interaction of wire and rectangular loop

In this video, Prof. Lewin shows an infinitely long wire and a rectangular loop at a distance $r_1$ from each other, each carrying a current. He then calculates the magnetic field resulting from the ...
0
votes
1answer
27 views

What would happen if a magnet was pushed towards a copper tube in space?

So the question was inspired by one of curious comments on youtube. What exactly would happen if you pushed a strong neodymium magnet towards the copper tube (aiming for the opening in an effort to ...
6
votes
4answers
616 views

Tokamaks and the reason they are still not efficient

I'm curious about why tokamaks are inefficient as generators. In laymans terms, what is the main reason(s) tokamaks still cannot be used as generators? My limited understanding of tokamaks tells me ...
0
votes
0answers
17 views

What is the physical meaning of a magnetic conduction current?

In electrodynamics, it is possible to have an electric conduction current, whereby $J=\sigma_e E$, with $J$ being the current, $\sigma_e$ the electrical conductivity and $E$ the electric field (this ...
-1
votes
0answers
38 views

How is liquid magnet possible? [closed]

My lector has made a liquid magnet. How's that possible? And how does it work? Thank you
4
votes
1answer
58 views

Is diamagnetism a static or dynamic effect?

When we put a diamagnetic material in the presence of an external magnetic field $\vec B_0$, the magnetic field inside the material decreases to $$\vec B=(1+\chi_m)\vec B_0,$$ where the magnetic ...
0
votes
3answers
129 views

Why geologist do not consider molten iron in the magma to be the source of Earth's magnetic field?

This was a question that came in a exam. How come is this possible? Actually, a question on the source of Earth's magnetic field was asked here on physics SE, which matches my opinion. The ...
4
votes
3answers
568 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 ...
0
votes
1answer
22 views

Net magnetic field in a loop

The Ampere's law states that the net magnetic field in a loop is proportional only to the current inside the loop. So if we calculate the net magnetic field in figure 1 and figure 2 we would obtain ...
0
votes
2answers
732 views

How does the magnetic field get induced in car's tire?

I was amazed to see how my car's tire started attracting the nuts and bolts, how in the world did it induce the magnetic field? Never heard of such phenomena!!!
0
votes
3answers
250 views

What determines the magnitude of force of an electromagnet?

Let's assume that there is an electromagnet with $B = 1 Tesla$ , what is the magnitude of the force it could generate on other dipoles equal to it's surface area? Can the magnitude of force (in ...
0
votes
0answers
25 views

The velocity of the charged particle in the magnetic field [duplicate]

Enrico Fermi considered that moving charged particle gains energy in the magnetic field, so its velocity increases. According to the Lorentz Law $\vec F=q\vec v\times\vec B$. Work is $A=\vec ...
1
vote
4answers
780 views

Where are the poles in a magnetic field generated by a current carrying straight conductor?

Consider the magnetic field generated by a straight current carrying conductor. Where are the poles?
-2
votes
1answer
12 views

Realigning of atomic structure by dissolving and electrowinning(electro extraction)? [closed]

Can the atomic structure(that makes up the magnetic domain) be realigned by dissolving a neodymium magnet(that has been demagnetized permanently) with acid(aqua regis or HNO3) and thus separating the ...
1
vote
1answer
388 views

Force of a solenoid on a ferromagnetic material

As I was trying to find an answer to another problem, I was informed that the equation I was using would not work. The equation I was using was $$F = (NI)^2\mu_0\frac{\text{Area}}{2g^2}$$ If this ...
-3
votes
0answers
17 views

Magnetic field of a cylindrical conductor with a hole in it [closed]

Can someone explain to me how they get $\hat{\varphi}_2$ in terms of everything else?
1
vote
1answer
32 views

spinning compass

There is an area where I live that prevents my compass from giving a solid direction; instead it just spins. Does this mean that this area lacks a magnetic field, or has to many of them for my ...
23
votes
4answers
9k 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 ...
1
vote
1answer
886 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 - ...
4
votes
1answer
332 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 ...
0
votes
1answer
203 views

What is the magnetic flux density “outside” the solenoid when AC current is passing through it?

I know that there are well defined equations explaining the magnetic flux density in the solenoid. However what about magnetic field outside the solenoid? How is the magnetic flux density related ...
0
votes
0answers
16 views

How can I approximate calculate the magnetic force between electromagnets?

I try to find an approximate amount of force exerted between two electro magnets. The below site could've helped me but the problem is that the below just talks about the number of coil turns and so ...
0
votes
1answer
53 views

Magnetic field induce photons?

So silly question, can a oscillating magnetic field excite electrons around atoms such that they produce photons (In other words can an applied magnetic field increase the energy level of electrons ...
1
vote
1answer
166 views

What is blocking the magnetic field of this neodymium magnet?

I opened up my hard drive and pulled out (among other things) the top and bottom braces for the reading arm. Each bracket contains a really powerful neodymium affixed to its underside. When the ...
0
votes
1answer
29 views

Eddy currents in a superconductor

Just had a lesson we just had our teacher introduced the concept of eddy currents, and showed us how a magnet moves slowly through a metal tube due to the opposite generated magnetic field. If you ...
1
vote
1answer
345 views

Calculating the magnetic field from rectangular conductor

I want to apply the Biot-Savart law to calculate the magnetic field at a point created by current flowing through a square/rectangular conductor. More specifically, a trace on a printed circuit board. ...
0
votes
0answers
19 views

Magnetic susceptibility anisotropy

I have some problems in understanding magnetic susceptibility anisotropy. I know that magnetic susceptibility can be described via a rank 2 symmetric tensor so the magnetization induced in a sample is ...
1
vote
1answer
141 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 ...
0
votes
1answer
27 views

Finding the electric field in a bar moving through a magnetic field [closed]

In this diagram: I'm supposed to find the electric field through the bar at equilibrium. I know that at equilibrium, the accumulated positive charge on the bottom of the bar results in a field that ...
0
votes
2answers
2k views

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 ...
1
vote
3answers
50 views

Ampere's law for a rectangular plate?

If a conductive wire was carrying current $I$, it would create a magnetic field: $$B=\frac{\mu_0I}{2\pi r}$$ However, if it's not a wire, but instead a plate how would the expression change/adjust ...
0
votes
0answers
18 views

Precession or projection?

A spin of 1/2 in a magnetic field is known to rotate around the direction of the field. But then it is also stated that it must be projected spin up or down. Is this simultaneous or happens after ...
0
votes
0answers
35 views

RL vs RLC circuit magnetic field

If I want to create an alternating magnetic field using an inductor, what difference would it make to use a series RL or a series RLC circuit ? How will the presence of a capacitor affect the magnetic ...
0
votes
1answer
733 views

Magnetic fields in transformers and back emf?

i am having some trouble with understanding the magnetic fields inside transformers and how they relate to back emf. My first query is: is the magnetic field produced inside the soft iron core ...
0
votes
1answer
25 views

Magnetic field of a solenoid vs magnetic circuit

The magnetic field in the middle of a solenoid is : $$B = \frac{\mu_0 N I}{L}$$ where L is the length of the solenoid The magnetic field in the air gap of a magnetic circuit with constant cross ...
-1
votes
0answers
25 views

Torque of a current loop (circular) inside another one

I have a circular coil of 12cm of radius that conducts a current of $13A$. A second coil, with 50 turns, and a current of $1.3A$ is in the certer of the other one. I need to find: a) the magnetic ...
0
votes
2answers
31 views

Direction of magnetic field

How did we know that the direction of magnetic field is from north to south and not the opposite? For example, we may use iron filings, and they will take the shape of the magnetic field, but how we ...
8
votes
5answers
491 views

Can one deduce absolute motion through magnetism? [closed]

I am trying to understand forces in relativity: Suppose there are two electrons A , B travelling side by side at 1 cm distance at .99 c (in space or at lHC, ignoring all other factors). I know that ...
0
votes
1answer
35 views

Biot–Savart law for a finite wire or the center of a square coil

I need to find the magnetic field inside the center square of a coil (I think this is the name, I'm translating, but if not, I'm talking about a loop of a wire, just 1 turn) of side $50cm$. So, I ...