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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18 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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5answers
85 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 $v$. If there exists a magnetic field such that there is a force on the current carrying ...
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23 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. ...
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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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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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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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64 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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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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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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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
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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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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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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124 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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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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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
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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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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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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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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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
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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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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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1answer
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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
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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
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
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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
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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 \...
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29 views

Electric field due to changing uniform magnetic field

I think this could be a misunderstanding on my part , still I want to clarify this.Suppose in a region of boundless expanse, there is a uniform magnetic field which changes at a rate $\frac{d\phi}{dt}$...
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Force per unit area on conducting sheet in magnetic field [closed]

Question from I.E. Irodov (3.260) I’m having trouble with the (c) part because the external magnetic field should be towards the right to give such a result,hence the force on unit area ...
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1answer
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Is the field strength in a Helmholtz coil really a function of current?

As I understand it, the field strength at the midpoint of two Helmholtz coils is given by: $$B=\left(\frac{4}{5}\right)^{3/2} \frac{\mu_0 nI}{R}$$ All things being equal, it seems that we can ...
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2answers
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How does magnetic field know the particle's velocity? [closed]

The force on one charged particle due to a uniform magnetic field is $F=qvB\sin\theta$. According to this formula, the faster the particle's velocity, the greater the force of the magnetic field is ...
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1answer
49 views

Will pyrolytic carbon/graphite repel the Sun's solar wind?

Since a moving charged particle has a magnetic field, as well as an electric field, and pyrolytic carbon/graphite repels an external magnetic field, would this mean that an object made out of ...
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What's the difference between the magnetocaloric effect and the thermomagnetic one?

I do not really understand the difference between the magnetocaloric effect and the thermomagnetic one. From what I gather from Wikipedia, one is just the reverse of the other. Namely, the influence ...
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1answer
62 views

An absurd consequence of magnetic field as an axial vector

One of the definitions of magnetic field (in free space): Force on magnetic north pole per unit pole. Magnetic field is an axial vector. So it changes its sign when we use left handed coordinate ...
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1answer
40 views

Different formulas for magnetic flux

I am familiar with the formula $\phi=BA\cos(\theta)$ fo magnetic flux, where I know $\theta$ is the angle between $B$ and $A$. I came across another formula ; $\phi=Ba\cos(\omega t)$. Wanted to ask ...
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1answer
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Magnetic Field Manipulation

For a reference of my level of knowledge, I have taken an undergrad electromagnetism class, and it wasn't pretty but I passed. I have a real interest in this so I don't mind doing more research. If ...
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1answer
59 views

EM-Wave: Calculate magnetic field $H$ from electric field $E$

In an exercise I am supposed to calculate the magnetic field from the electric field for a plane, harmonic wave in vacuum. $$\vec{E} = - E_0 \cdot \sin(\omega t - k z) \cdot \vec{e_y}$$ Using the law ...
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1answer
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Dimagnetism proof for superconductivity

I came across an article that dimagnetism is one of the proof so that a material can act as superconductor. So what is dimagnetism.
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Electromagnetism: What do $B$, $H$ and $M$ field lines look like? [duplicate]

I can't understand the meaning behind this picture For the magnet (upper half of picture), it is said that $\oint$$\vec{H}\vec{dl}=0$ because there are no currents in the magnet (non Ampere's ...
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3answers
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A strong neodymium magnet has no effect whatsoever on my phone compass. How is that possible?

If I hold a strong neodymium magnet near my iPhone while the compass app is running, there is no effect whatsoever on the compass bearing. It doesn't matter where I hold the magnet in relation to the ...
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Why doesn't Venus have a magnetic field? How does the speed of rotation affect the magnetic field of a planet?

Why doesn't Venus have a magnetic field? How does the speed of rotation affect the magnetic field of a planet?
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1answer
50 views

What happens if permanent magnets are placed under electric field?

I understand that ferromagnets have domains that align parallel to the applied magnetic field, in which the spin of the unpaired electrons line up. But I am curious as to what happens to such magnets ...
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1answer
50 views

Is this the Melvin metric (magnetic universe) in disguise?

I'm solving the Einstein equation assuming a cylindrical symmetry and found something interesting which I never saw elsewhere. I now feel that I may have found the Melvin magnetic universe solution ...
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1answer
38 views

Electrons direction in cathode ray tube

This image below show the movement of an electron in a magnetic field, it's taken from the video [Histoire des sciences] La découverte de l'électron explaining the experience of J.J. Thompson when he ...
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1answer
33 views

Potential drop across inductors in DC circuits

The potential drop across an inductor is equal to $L(di/dt)$ where $L$ is inductance coefficient. But according to this in a DC circuit there should be no potential drop across the inductor (because $...
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0answers
107 views

Should a Bismuth coin slide slowly down a magnetic ramp?

One way to check for counterfeit silver/gold coins is to "slide" them down a ramp made of neodymium magnets. You can see an example here, or just look up "silver slide". I have seen this work for ...
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2answers
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How is the magnetic flux density inside a current tube affected by an inner wire?

Background to problem Conventional wisdom informs that the magnetic flux density inside a tube carrying current is zero everywhere. Pictorially this is represented by this finite element analysis (...