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0
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1answer
38 views

What is $dB/dx$ where $B$ is magnetic field and $x$ is the separation between two magnetic dipoles?

I came across a question regarding the force between two magnetic dipoles $M_1$ and $M_2$ separated by a distance $x$ . Here in this text book I am given the solution is $$ B = \cfrac{\mu_0}{4 \pi}...
-1
votes
0answers
14 views

Detecting if there was a repulsion or attraction on a magnet

I would like to know if we have a way of detecting if a magnet reacts to a iron bar or attract /repel by another magnet. Would be able to see through a sensor if there was some activity in the ...
0
votes
1answer
26 views

Why is there no B-field parallel force on an electron orbiting a magnetic field line?

If an orbiting electron creates a toroidal magnetic field like a ring of current does, and this field is oriented opposite to the magnetic field line the electron is orbiting, then why is the electron ...
2
votes
1answer
53 views

How would a cloud of ortho-positronium atoms behave near a magnetic dipole?

The force on a macroscopic magnetic dipole with dipole moment $\mathbf{m}$ in an inhomogeneous magnetic field $\mathbf{B}(\mathbf{r})$ is given by $$\mathbf{F} =\nabla (\mathbf{m} \cdot \mathbf{B}(\...
0
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0answers
19 views

Calculate the force acting on a magnet inside a solenoid wrapped in Iron

Sounds like a simple question, doesn't it? But it isn't and it has been frustrating me to no end. First, my setup is fairly straightforward: I am building an electromagnetic actuator and have a magnet ...
3
votes
1answer
56 views

Can someone explain how magnetic potential energy can exist even though the field is non-conservative?

$U=-B\cdot \mu$ is defined to be the magnetic potential energy, I saw this in my lecture notes, but we had already talked about the fact that since the work done to move a charge there is path ...
0
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0answers
23 views

The magnetic and electric dipole moment 'popping out' from multipole expansions

I interpret electric dipole moments and magnetic dipole moments as intrinsic properties of certain materials, but in Griffiths it's literally picked out of expressing the potential and magnetic vector ...
0
votes
0answers
23 views

Hysteresis in Magnetoresistance

I am measuring the magnetoresistance of a thin ferromagnetic film from -1T to 1T, it looks something like this - The magnetoresistance increases slightly between 0 and coercivity of the film and then ...
-1
votes
1answer
39 views

Inconsistencies in finding magnetic vector potentials

Recently I've been studying for my electromagnetism finals and I reached a question about magnetic vector potentials. If I have a wire with constant current distribution, what is the magnetic vector ...
0
votes
1answer
37 views

Confusion regarding torque given by M×B

The magnetic torque acting on a loop of magnetic moment M placed in a magnetic field B, is given by τ=M×B. My question is, about which axis does this give the torque about? Is it the instantaneous ...
2
votes
1answer
58 views

If electricity creates a magnetic field, could a (strong) magnetic field stop electricity? [closed]

Surely this would make the two magnetic fields interact and if movement was made impossible, the stronger magnetic field would block the weaker electromagnetic filed. Am I right (presuming that the ...
3
votes
1answer
64 views

Can $F=qvB$ be applied to a solenoid and a parallel moving magnet?

If you take a scenario like this, Charge gathers at either end, and if you could somehow form a complete circuit without there being a canceling effect, there would be a current flowing. This makes ...
1
vote
0answers
31 views

How a sphere can be assumed as dipole?

From the book introduction to electrodynamics by David Griffiths , fourth edition, page no 279, there is an example to find the magnetic field of uniformly magnetized sphere. It said the magnetic ...
0
votes
0answers
8 views

Is positive and negative magnetostriction attributed to the shape of the domains?

I have been reading up on magnetostriction, and noted that some materials expand while other contract in the direction of an applied magnetic field, and that it is attributed to the rotation of the ...
0
votes
0answers
24 views

how much magnetic field is experienced at the centre of bar-magent?

What is the magnitude of magnetic field at the centre of bar magnet? What's its mathematical expression?
0
votes
1answer
72 views

Why do we think that the relation $\vec{\mu}_L=\frac{e}{2m_e}\vec{L}$ will be valid in quantum mechanics?

Assuming the electrons to revolve round the nucleus in circular orbits and using the fact from classical electromagnetism that a current loop behaves like a magnetic dipole of dipole moment $\vec{\mu}...
0
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0answers
22 views

Sine or cosine component of force on current carrying coil in a magnetic field

For calculating torque on a current carrying loop in a magnetic field, restoring torque that is, we use the $\tau=\vec{m} \times \vec{B}$ where $\vec{m}$ is the magnetic moment and $\vec{B}$ is the ...
2
votes
3answers
116 views

Is magnetic force relativistic effect or intrinsic property?

In this video, they explain that magnetic force is an effect of electric force due to special relativity. https://www.youtube.com/watch?v=1TKSfAkWWN0 But then, the same authors explain in this video ...
0
votes
1answer
42 views

Force on a magnetic dipole in an external magnetic field

I want to find an expression for the force acting upon a magnetic dipole with dipole moment $\mathbf{m}$ if that dipole is positioned in a stationary, external magnetic field $\mathbf{B}$. The ...
0
votes
0answers
17 views

Magnetic material demagnetization through Curie temperature

It is known that some materials lose their permanent magnetic properties when they are heated above certain temperature known as Curie temperature or Curie point. As those materials are cooled down to ...
0
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0answers
13 views

Parameters Affecting Demagnetisation

What parameters will affect how a ferromagnetic material is demagnetised? Assuming that only changing fields will induce demagnetisation (although I suppose I could well be wrong on that one), what ...
0
votes
1answer
99 views

Magnetic field around solenoid and toroid

Solenoid is proving a little bit confusing While getting through solenoid I found that the field outside it is extremely small and is negligible. Also the field at ends is half of that of center. ...
0
votes
2answers
35 views

Magnetic moment of a radially symmetric current

In my latest assignment I'm tasked with finding a magnetic moment $\mu$ of a hydrogen atom, whose current distribution $\mathbf{j}(\mathbf{r})$ looks like $$\mathbf{j}(\mathbf{r})=\frac{e\hbar}{3^8 \...
3
votes
2answers
311 views

Two questions about electron's magnetic spin

Does electron's magnetic spin mean that we can think of it as having the two magnetic poles? Does the spin mean that it generates magnetic field even if it is at rest? I expect to get 'no' to both ...
1
vote
0answers
35 views

How much time does it take magnetization to appear, after turning on a magnetic field?

When a magnetic field ${\bf H}$ is turned on from zero, a piece of material, not previously magnetized, exhibits a magnetization ${\bf M}$ due to ${\bf H}$. According to ${\bf M} = \chi {\bf H}$, ...
0
votes
1answer
124 views

Are permanent magnets a relativistic effect?

The relationship between Electromagnetism and Special Relativity is something that always amazed me but I haven't fully understood yet. Misconceptions and contradictions seem to be widespreaded, and ...
0
votes
1answer
36 views

Magnetic Shielding

Imagine a substance in an electric field. You don't want the electric field to interact with the object you have put in its way. What should be the type of material this magnet should be made of to ...
0
votes
1answer
29 views

Which factors determine which pole is going to be N and S in the broken pieces of the magnet?

Let's suppose that there is a magnet with a north and south pole and we break this magnet randomly. Which factors determine which pole is going to be N and S in the broken pieces of the magnet.
0
votes
1answer
32 views

Stationary electromagnet(s) to move a metal rod.

I would like to use an electromagnet(s) to move the metal rod depicted bellow in the side view, it moves in the direction of the arrow the rod requires 5.39N of manual force to travel in the depicted ...
2
votes
1answer
62 views

How are these “supplementary” or “satellite” Helmholtz coils used?

Three mutually orthogonal pairs of Helmholtz coils can be used to produce a fairly uniform magnetic field of arbitrary direction within a certain volume, and/or to null/cancel an external field (e.g. ...
4
votes
1answer
213 views

When does $\nabla \times B =0$?

In my lab, I use electromagnets to apply a magnetic gradient force to lots of very small (superparamagnetic) nanoparticles embedded in an elastic medium. I believe that these can be treated as ...
0
votes
1answer
69 views

Why magnetic dipole moment are important

After reading the Chapter 35 of Halliday Resnick and Krane's Physics, which is the section on magnetism in which magnetic dipoles are introduced, I still don't understand why the particular quantity ...
0
votes
1answer
38 views

Permanent magnets - Attraction with no repulsion

I have some permanent "refrigerator" magnets and noticed that, though they attract the refrigerator, they also attract each other (there is only one side available for the magnet, the other side has a ...
2
votes
1answer
48 views

Reversing magnet polarity to increase/decrease Eddy currents?

I have a cast iron wheel with magnets around the inner radius as a braking mechanism. If I were to add additional magnets around the outer radius, would the amount of Eddy currents increase or crease ...
1
vote
2answers
30 views

Joining poles of bar magnet

What happens when 2 poles(i.e. noth and south) of the same bar magnet joined to each other to form circular loop?
1
vote
2answers
258 views

Why are there sine and cosine in the magnetic dipole moment (in the torque formula) of a rotating conductor loop?

I'm trying to redo the textbook example in magnetostatics. The current carrying loop is affected by a magnetic flux in the ax→ direction. While trying to find the torque on sides ab and cd for figure ...
-2
votes
2answers
82 views

Does the magnetic field line passing along the axis of a bar magnet ever reaches to South Pole?

Consider a bar magnet, and the magnetic field line that goes through its axis and through the center of its north pole and thus follows a straight line path out of the magnet. Will this line ever be ...
4
votes
2answers
117 views

Special relativity constrains massless electric dipoles, but not massless magnetic dipoles?

Discussion in comments on the two questions linked below leaves me confused about the following point. We expect a magnetic or electric dipole to make a field that has some universal transformation ...
2
votes
2answers
228 views

Why is a current carrying loop considered a dipole?

I am unable to understand why a current carrying loop is considered a dipole. Why exactly is it called a "dipole", which two poles are we referring to and how do those two poles function as the north ...
1
vote
2answers
174 views

If I use a magnet to levitate another magnet, where is the energy coming from?

Imagine I use one static magnet to levitate another magnet indefinitely. This levitating magnet is in a narrow tube that wont allow it to rotate and get attracted. So it will keep levitating forever, ...
21
votes
1answer
1k views

Why is Ampère's law violated if there are no fringe fields?

What's wrong in this diagram? The reason is this: magnetic field lines between the two poles of magnet are perfectly straight in the given diagram, which is not possible. Fringing effect of the ...
0
votes
1answer
162 views

Magnet going through a current carrying loop

Consider a small magnet that is suspended just above a conducting fixed loop placed. The magnet is oriented perpendicular to the axis of the loop and is released to fall under gravity and at the same ...
2
votes
0answers
44 views

Force caused by the magnetic field on the electron spin

I have read there are two ways to express the force caused by a variable magnetic field over a magnetic moment depending on the source of the magnetic moment since it can come from a dipole or a loop ...
3
votes
1answer
366 views

Why is the spin magnetic moment of an electron equal to the orbital magnetic moment of a hydrogen atom?

The intrinsic magnetic moment of an electron is equal to the magnetic moment that we obtain by effects of orbital motion of a hydrogen electron in the lowest shell (1 Bohr magneton), using classical ...
1
vote
0answers
66 views

B-field and H-field opposing inside ferromagnets

I was studying Ferromagnets from several books where the authors would just state that its a notable feature of ferromagnets that, in an external B-field, the H-field opposes the B-field inside the ...
3
votes
2answers
287 views

Inductive sensor - How does it work?

I can't understand how the system sketched here physically works: 4 = permanent magnet, with residual magnetization $B_r$ 6 = ferromagnetic core with a coil around it 7 = ferromagnetic toothed ...
1
vote
0answers
119 views

Diamagnetic materials with negative susceptibility?

I have been learning about magnetostatics, and from reading about the existence of diamagnetic, paramagnetic and ferromagnetic materials I was under the impression that a limiting value for magnetic ...
1
vote
0answers
415 views

Surface current density (magnetic materials)

In deriving the boundary conditions for $H$ at the boundary between two media, my lecturer stated that "since there is no conduction (free) current on the Surface... the tangential components of H are ...
0
votes
1answer
464 views

How is the Magnetic flux density derived from the curl of the vector potential?

I have two questions. Firstly, how is the equation solved after taking the curl of A(r) here. How did they arrive at the final expression for B(r). I tried taking the product rule for curl, but got ...
3
votes
1answer
57 views

Can you make electricity from the bound charges in magnets?

Magnetostatics is the study of magnetic fields in systems where the currents are steady. If inside magnets that give off magnetic fields there are bound charges, is there any possible way to make them ...