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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6answers
105 views

Why is it assumed that magnetic forces arising from magnetic fields do not do work on a current carrying conductor?

Imagine a long, thin current carrying conductor carrying a current I and moving through space with a velocity $\mathbf v$. If there exists a magnetic field such that there is a force on the current ...
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0answers
18 views

Is the current in wire is a magnet?

What I understand (Tell me if I am wrong): There are two types of magnets, Permanent Magnets (eg. Bar Magnet ) and Temporary Magnets (eg. Electromagnet ). Permanent magnets create a permanent ...
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0answers
22 views

Hysteresis in ferromagnets

In my text it is given that the magnetic susceptibility X = I/H but in another it was dI/dH. But second can be used to draw the hysterisis graph so I think the second must be correct. X is dependent ...
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1answer
821 views

Magnetic field lines vs. Electric field lines

What's the difference between magnetic field and electric field lines? Does $d\vec B$ point in the direction you would experience a force if you were a moving charged particle at that point? I know ...
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0answers
51 views
+50

Stability of a dipole magnet undergoing eddy current braking in a cylindrical tube

Consider a cylindrical dipole magnet with strength $B$ undergoing eddy current braking in a conductive cylindrical tube with the axis of the magnet aligned with the axis of the tube. The magnet ...
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1answer
24 views

Does magnetic intensity ($H$-field) 'conduct' through a material

We've been taught by our lecturer that magnetic intensity propagates through a material. But I have a doubt because I feel that it is not consistent with Ampere's law. My reasoning is explained below. ...
2
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1answer
60 views

Which form of Lagrangian should I choose for uniform magnetic field?

Here's the problem and corresponding question. Let's consider a uniform magnetic field $\vec{B}=B_0\hat{z}$. Looking for the solution of vector potential satisfying $\vec{B}=\vec{\nabla}\times \vec{A}...
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5answers
788 views

Why does more rapidly changing magnetic field induce greater EMF?

I am confused about the above question. I know that when you move a magnet in and out of a close loop of wire, you induce a EMF in the wire. The change of moving the wire in a out of a wire is what is ...
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0answers
35 views

Magnetic Effects of Electric Current [on hold]

An electron being accelerated through 100V enters a unifiorm field of 0.004Tesla perpendicular to the direction of the motion. Calculate the radius of the path.
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1answer
1k views

If we put diamagnetic material under strong electromagnet.Would the opposing magnetic fields strong enough to attract ferromagnetic materials?

Suppose we put a diamagnetic material (such as Bismuth or Pyrolytic Carbon) under a strong magnet (see image below). It would create opposing magnetic fields. Would the opposing magnetic field be ...
4
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1answer
835 views

Graphene - Can it produce a magnetic field?

So it's probably a quick no on this one, but since I haven't majored in physics or chemistry I have no idea if it's possible to make Graphene generate a magnetic field. Assuming power or current is ...
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0answers
65 views

Speed of the Earth through universe [closed]

If two negatively charged spheres repel each other in the same way indipendently of Earth velocity does the movement of the Earth around the Sun which is at a short moment in direction with the Milky ...
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1answer
114 views

At what point does the SMOT device actually stop working?

The SMOT device described in Wikipedia is said to cause a metal ball to roll uphill and then fall off the ramp. I understand that perpetual motion is not possible. However, reading through the ...
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1answer
792 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 ...
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1answer
166 views

On the magnetic field in the Meissner effect

As shown in the figure, in the Meisner effect, the magnetic field of the magnet bypasses the superconductor. My question is, does the magnetic B field belonging to the magnet increase at the arrow ...
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0answers
28 views

Software for 3D magnetic field simulation [closed]

What are some user friendly softwares for making customized 3D models and doing magnetic field simulation. I have used FEMM for 2D models and it works great but is not capable of doing 3D models.
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0answers
37 views

Motion in Uniform Magnetic Field

Sorry for asking an exercise question here, but I'm really having difficulty figuring this one out. Quick summary of the problem: a charged particle moving in a uniform magnetic field will experience ...
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0answers
21 views

Why is there a negative sign in the (non-relativistic) bivector formulation of the Lorentz force?

I'm currently trying to update my understanding of basic (Newtonian, non-relativistic) physics to use bivectors and Clifford products instead of pseudovectors and cross products. And I've come up ...
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1answer
69 views

Experiment: Magnet falling in a copper/aluminum pipe

We know that when we release a magnet in conducting pipe (aluminum, copper, etc..) it will be subjected to a magnetic force induced by the induced current. This magnetic field will be created in a ...
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1answer
293 views

Finding the induced current in a loop and force acting on the conductor

The conductor has a velocity to the right and is part of a closed loop (see the picture). Find the direction of the induced current and the direction of the magnetic force on the conductor There must ...
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1answer
32 views

Potential Drop across Inductor VS Potential drop across Rotating coils in $B$-Field

I was trying to understand the difference between the Back emf generated across Inductor due to change in current and Back Emf Generated across a coil that is rotating in presence of B Field. ...
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0answers
23 views

Wavefunction and associated energies of particle in uniform magnetic field [closed]

I'm trying to find the wavefunction and associated energies of a charged particle in a uniform magnetic field . We have the following hamiltonian: $$ H = \frac{(-i\hbar\nabla -q\vec{A})^2}{2m} $$ ...
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1answer
125 views

Are photons emitted by a magnet?

If you put a photon detector near a magnet (with the magnetic field static in time), is there some probability that the photon detector will detect a photon? Does QFT not predict that a photon could ...
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2answers
32 views

Net bound current with uniform magnetization

My confusion stems from the following: Can I reason the answer being (D) analogous to... for instance: If this was instead a solid cylinder with uniform polarization $\mathbf P$ pointing in the z-...
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1answer
33 views

Do we need to know Earth's magnetic field locally?

I'm a high school student and in our course we have elements of earth's magnetic field (dip and other stuff) that lets us know the value and direction of magnetic field at any point on the planet. I ...
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0answers
22 views

Finding magnetic flux density of a point a certain distance away from the curved face of a disc magnet [closed]

I have used this website here because I am trying to find a formula that will tell me the magnetic field strength (B) of a point a certain distance away from the curved part/round face of a circular/...
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1answer
115 views

Building huge magnetic field gradient

Looking at how MRI works, I came across the fact that the spatial resolution depends on the magnetic field gradient, this gradient being created by "gradient coils". I was not able to find what the ...
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2answers
825 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
37 views

If a 1lb magnet with a 100lb load was levitating; would the force pressing down be less than or equal to a 101lb weight that wasn't levitating?

My guess is that it would require the same amount of force to lift the same amount of weight regardless if levitating or not. That may be a seperate question. I suppose this question could be ...
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1answer
5k views

Solenoid vs coil of wire

This may sound pretty basic, but: I'm studying for my AP Physics exam, and I am confused. Apparently, the formula for the magnetic field in the center of a loop of wire with $n$ turns is: $B=\frac{\...
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0answers
33 views

Interpretation problem with Melvin and Bertotti-Robinson magnetic universes

I'm having an interpretation problem with two models of magnetic universes in General Relativity. Firstly, consider the Melvin universe described by the following static metric: \begin{equation}\tag{...
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1answer
183 views

Magnetic energy stored in a conductor

So I came across with following problem: Consider a cylindrical conductor of infinite length and circular section of radius a and that is traversed by a stationary current I. What is the magnetic ...
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3answers
1k views

How specifically does an MRI machine build an image from received radio waves? [closed]

Unlike the excellent Wikipedia page on ultrasound imaging, the one on MRI only explains the principle theory behind MRI - that oscillating strong magnetic fields cause water molecules to emit ...
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2answers
41 views

Does a particle's rotational kinetic energy change when it enters a uniform magnetic field?

Consider a charged particle entering a uniform magnetic field with some constant velocity perpendicular to the magnetic field. I know that the particle will follow a circular path within the magnetic ...
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2answers
1k views

Biot-Savart law from Ampère's with multivariate calculus

Let us assume the validity of Ampère's circuital law $$\oint_{\gamma}\mathbf{B}\cdot d\mathbf{x}=\mu_0 I_{\text{linked}}$$where $\mathbf{B}$ is the magnetic field, $\gamma$ a closed path linking the ...
2
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1answer
198 views

Do magnets attract magnetic materials by inducing magnetism in them?

Here are 2 concise excerpts from a book I have been reading:- 1.A permanent magnet produces its own magnetic field. An induced magnet is a material that becomes a magnet when it is placed in a ...
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0answers
22 views

How to calculate the velocity and radius of curvature of a charged particle in a perpendicular magnetic and parallel electric field?

If I have a charged particle come from a point velocity V1 where there is a uniform electric field parallel to the motion of the particle which accelerates it and a magnetic field perpendicular to ...
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0answers
16 views

How can I calculate magnetic field strength of a variable gap magnet?

I am currently doing an experiment where an aluminium pendulum is passed through a variable gap magnet (creating eddy currents). The variable I am changing is distance between the two grade N35 ...
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2answers
122 views

Derivation of Ampere's Law from Biot-Savart

Our aim is to derive $\nabla\times \mathbf B=\mu_0(\mathbf J+\epsilon_0\frac{\partial E}{\partial t})$. To begin with, let $ \mathbf A=\frac{\mu_0}{4\pi}\int_{\mathbb R^3}\frac{\mathbf J(\mathbf r')}{...
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2answers
46 views

Can magnetic field change kinetic energy?

An electron and a proton are moving under the influence of mutual forces. In calculating the change in the kinetic energy of the system during motion, one ignores the magnetic force of one on another. ...
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3answers
121 views

How to determine the concentration and sign of the charge carriers in copper

I need to design a procedure for an experiment to determine the concentration and sign of the charge carriers in copper. I'm given: A slab of copper 2.0 mm thick, 1.5 cm wide, and 4 cm long One very ...
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1answer
19 views

Why do magnetic field lines wrap around the other side of a super diamagnet instead of redirecting completely away?

Super conductors are perfectly diamagnetic in that they perfectly expel a magnetic field. To me that means that if the source of a magnetic field is on one side of a super conductor, the other side ...
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1answer
38 views

How electric field and magnetic field propagate through vacuum where there's no charge present? [duplicate]

As we know light travels as an electromagnetic wave...but electric fields and magnetic fields are interactions between charges...they are the forces acting on stationary and moving charges ...
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1answer
23 views

Working out the radial arc of a magnetic field to get mass of electron

We have an experimental setup as below, the magnetic field strength, Bq/30s, and distances (magnet distance, Geiger counter height, Geiger to magnet centre distance) have all been recorded. The energy ...
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1answer
40 views

Regarding the use of Ampere's Law

i wanted to calculate $\mathbf{B}$ of these two parallel wires, and i've taken a glance at the correction and i've found out this equation, i tried to understand it but in vain, where do $(x + \frac{d}...
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2answers
122 views

Semi-classical derivation of maximal magnetic field in the Universe

I'm looking for all (or most) theoretical semi-classical derivations of the maximal magnetic field intensity that there may be in the Universe. As an example, this paper evaluate a maximal field of ...
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2answers
39 views

Evaluating an Integral with a Cross Product

Problem: A infinite thin spherical shell with radius $r_0$, centered around the origin, is homogeneously charged with surface-charge-density $\sigma$ and rotates with the constant angular verlocity $\...
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1answer
47 views

What is a permanent magnet and how do I calculate the magentic force exerted by a permanent magnet?

So far my understanding of a permanent magnet is: Since elements like iron have atoms with orbitals that have many electrons with the same spin, these cause the metal to have a magnetic field, which ...
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1answer
118 views

Does electric and magnetic field interact?

Can electric field or magnetic field interact with an Electromagnetic radiation? And can 2 electromagnetic radiations interact with each other? Rather than the interference effect.
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1answer
26 views

Magnetic field due to a dielectric sphere

There is a nice example in Griffiths where he calculated magnetic field of a spherical shell/sphere for uniform surface charge $\sigma$. The argument was, since the surface current is $K= \sigma r \...