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 [magnetism] tag, as questions about the phenomenon & theory of magnetism do not necessarily involve the discussion of fields.

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Is $\vec{B}=0$ in an infinite cylinder with localized magnetization?

Say we have an infinite cylinder, with constant magnetization $M(z)\hat{z}$ along its axis. This vanishes for large $|z|$, say like $e^{-z^2}$. It seems to me that the solution to the equations $$\vec{...
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Should the magnetic force on the edge of iron bar B attached to a magnet A with lenght of B - L beign calculated with relatve permeability constant

I am attaching a magnet on the edge of iron rode with length 0.1m as experiment, and i get much smaller attractive force on that far edge than expected. As expected it should be the relative ...
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Why does magnetic dipole's north pole pointing in the direction of magnetic field increases overall magnetic field?

I'm studying magnetic moment- current loop, electron/proton/charge revolving, magnetic dipole etc. This is about paramagnetism of materials. According to me magnetic dipole's south pole is attracted ...
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Magnetic susceptibility for ferromagnetic materials

Magnetic susceptibility $\chi_m$ is defined by following relation: $$\vec{M}=\chi_m \vec{H}$$ where $\vec{M}$ is the magnetization density and $\vec{H}$ is the magnetizing field, defined by $\vec{H}=\...
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Can we derive Ampere's Circuital Law from Gauss's Law or vice versa?

I was curious if it is possible to derive Ampere's Circuital Law from Gauss's Law as they are very similar and both can be applied for highly symmetrical problems $(Infinite\space wires,Rings..etc)$ ...
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Why do two magnets faceing eachother with opposite poles but offset horizontally repel?

When you place two magnets with opposite poles facing eachother vertically they attract. However if you move one magnet horizontally by a distance greater than the magnets diameter they will begin to ...
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INDUCTANCE depends on the number of turns in a solenoid. Is this the case with RELUCTANCE as well?

The total flux ($\Phi$ ) through an solenoidal inductor of length $l$ and $N$ turns is proportional to the current through the inductor and the inductance $L$ of the inductor according to $$\Phi =L \...
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Magnetic field lines are closed lines?

How is it proven that the magnetic lines are closed lines? Because the divergence of $\mathbf{B}$ is zero does not sound convincing, since fields like $\mathbf{F} = a\mathbf i +b\mathbf j+c\mathbf k$ (...
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What does the $4\pi k_{m}$ mean in Ampere's law?

On Wikipedia Ampere's law is written $$ \oint_{C} B \cdot dl = \mu_{0}I_{enc}$$ and in this resource by Kirby Morgan about Ampere's law it is written as $$ \oint_{C} B \cdot dl = 4\pi k_{m}I_{C}$$ ...
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Hello, I am wondering How I can set Equation which describing the motion of an object attracted to magnet

Umm, I imagined the sphere magnet (it can rolling) which has friction. then How I can do make formula about this? I know $$ E = \int \frac{B^2}{2\mu} \,dV $$ and that is same as $1/2mv^2$ ? and $I = 2/...
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Images off a surface of water in rotation

A simple experiment made with a forced vortex on a water surface enthralls me. Image of straight window glass edges get distorted. The experiment can be easily replicated. The first image is ...
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Can you please tell if there is anything wrong with the attached figure?

I think the direction of the magnetic field taken is itself wrong. In the given figure the direction of magnetic field of earth is taken to be B and H and Z are its respective horizontal and vertical ...
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Is the induced electric field in a current changing solenoid actually that what we call magnetic vector potential field?

Induced electric field $E$ in a changing current (i.e. changing magnetic field $B$) solenoid image creditis: https://faculty.uml.edu//Andriy_Danylov/Teaching/documents/L18Ch33InducedEcovered.pdf I was ...
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Question regarding exercise of dynamics of spin-1/2 system

Problem 5) Generic Quantum-Mechanical Spin-1/2 Dynamics Consider a spin-1/2 system in an external magnetic field, described by $H=\mu_s\mathbf{B}(t)\cdot\hat{\mathbf{S}}$ with $$\mathbf{B}(t) = B_0\...
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How to reduce magnetic field between two magnetic shield sheets (silicon steel sheets)?

I put 2 parallel silicon steel sheets between magnetic field as below: As silicon steel has much bigger permeability than air,magnetic line will go through 2 silicon steel sheets. What I can do to ...
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Do electric fences such as those typically used to fence cattle generate magnetic fields?

I'm using magnetometers near electric fences and I'm wondering if the electric fence should be detectable and if so, how close do I need to be to the fence for there to be a "measurable" ...
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Why is there no deflecting force between two bar magnets?

If we were to hypothetically place a magnet to the right of the magnet above with the North pole of the right magnet next to the South pole of the left magnet, from real-life experience, I know that ...
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What is the "pincentrum" for magnets in the molecule structure?

So my prof explained ferromagnetism and said that permament magnets have "pincentra" so the material becomes magnetic too because the magnetic domains all point in the same direction. I don'...
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What does the $B$ field refer to?

I'm just looking for some guidance, it would be nice if someone could explain this. So the $B$ field in $B=\mu H$, as I understand is the induced magnetic field in some material due to this material’s ...
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Finding the direction and magnitude of the net magnetic field due to two wires at a point P, (question from book)

So I found a physics question on a book which I attempted involving two wires with current flowing through them. The question provides the following information: . I was able to find the magnitude of ...
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Magnetization and thermodynamics [closed]

A magnetic needle is placed such that the magnetic field is parallel to its axis. I need to prove the following relation between the specific capacities where $M$ is the magnetization and H the ...
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Helmholtz Coil — What affects uniformity?

Does a high current affects the uniformity of the $B$ field in a Helmholtz coil? For example, I was wondering if it would affect the width of the flat region of the net magnetic field as seen below. ...
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Does a change in electric field cause a change in magnetic field, or do both just always happen together?

I'm taking an entry-level Physics class. From my understanding, a change in electric field does not "cause" a change in magnetic field, but rather, both just always happen together out of ...
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How is the solar magnetic field produced?

I have been trying to understand the magnetic field creation mechanism. I know that its origin is not perfectly understood, but what is currently believed (as I know) is that the magnetic fields ...
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Modeling the Effect of Magnetic Induction on Single Neurons

In this paper, the authors suggest a potential mechanism for magnetoreception in birds: as the Earth's magnetic field (taken to be homogeneous over sufficiently small spatial scales) passes through ...
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Would there be no electrostatic repulsion if you make two protons hit head on w.r.t their spin (i.e. opposite angular momentum)?

Basically the title. If you have two protons the have a strong electrostatic repulsion. However their spin produces a magnetic field and if you orient them like in the picture there would be magnetic ...
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At which point is the magnetic field in a current carrying loop the strongest?

At which point inside a circular current carrying loop the strongest? Some sources say it is at the centre and some say it is at the circumference. And how can we mathematically prove this? And also, ...
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How to calculate Electric and Magnetic Field of TEM waves through a coaxial cable?

So basically if you have a coaxial cable (inner radius a and outer radius b) with a dielectric between the two conductors (with permittivity ϵ and magnetic permeability µ ) and the monochromatic TEM ...
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Confusion about Lenz's law and change in magnetic flux

I'm not sure this type of question belongs on SE as it may seem more hw-e type, so please comment if it is not and I'll remove it For this problem, in particular b) where it asks "During the ...
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Would a ring magnet around a copper tube be slowed?

if a ring-shaped magnet was dropped with a copper pole through the center would it be slowed the same as a cylindrical magnet in a copper tube? if so would it be slowed more or less?
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Is there an analogous potential for magnetic moments in comparison to that of electric dipoles: $\frac{k \vec{p}\cdot \hat r}{r^2}$?

If I am not mistaken the electric potential of an electric dipole is given by: $$ V(r) = \frac{k | \vec{p}|\cos \theta}{r^2} = \frac{k \vec{p}\cdot \hat r}{r^2} $$ Where $\vec{p}$ is the electric ...
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Biot-Savart's law in magnetic medium

I have read that in a medium, $B$ changes but $H$ does not. So does this mean that in the expression for biot-savart's law $\mu_0$ can be replaced by $\mu$? I tried to look for biot-savart's law in ...
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Does spinning a diametrally magnetised rod magnet increase its magnetic field, like a Halbach Array?

A halbach array augments the magnetic field on one side and cancels it out the other. Moving along a linear Halbach array or positioned on the circumference of a spinning rotary halbach array (see ...
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Magnetic flux through a closed surface

I was reading Electromagnetic Induction, then I faced a understanding problem while reading the integral and differential form of Faraday's Law.. We know Magnetic Flux= ${\bf B} \cdot {\bf S}$ Where ${...
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Determination of the electric and magnetic field of a beam of protons as functions of the distance $r$ to the beam with the help of Ampere and Gauss

I want to calculate the fields $\vec{E},\vec{B}$ as a function of $r$. I know that the current implied by the beam is $I=env_{p},v_p=\frac{c}{3}$ and the charge density is $\rho=en$. On top of that, ...
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Is Farady's law valid for conducting loop only? [duplicate]

Is it applicable to a nonconductive loop? What if the loop consists of both non-conducting and conducting paths?
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Derivation of $~\nabla^2\mathbf{H}=\sigma\mu{\partial\mathbf{H}\over\partial\mathrm{t}}+\epsilon\mu{\partial^2\mathbf{H}\over\partial\mathrm{t^2}}~$

The following equation(subset of Maxwell's equations of electromagnetic wave(s)) is said held in free space. $$\underbrace{ \color{fuchsia}{\nabla^2\mathbf{H}_{}=\sigma\mu{\partial\mathbf{H}_{}\over\...
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Maximum $B$-field at the surface of a permanent magnet

I have the dipole formula for a permanent spherical magnet in coordinate-free form. $\vec{B}=\frac{\mu_{0}}{4\pi}\frac{3(\vec{m}\cdot\hat{r})\hat{r}-\vec{m}}{r^{3}}$ I am trying to find the maximum $B$...
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Why doesn't the EM field above the center of a charged current loop look like a bivector?

This is probably a silly mistake. I know that in relativity the electromagnetic field is a bivector. But I was thinking about the field on the axis of a circular current loop with a net charge. By ...
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Total Josephson current through superconductor junction with magnetic field

I am given a diagram of a Josephson Junction like so: With a magnetic field $B = \mu_oH$ in the z-direction. I'm reasonably sure $d_x,d_y,d_z$ are normal lengths, not infinitesimal lengths although ...
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Does magnetism play a role in the formation of galaxies?

Forgive my ignorance as I know next to nothing about physics. From my layperson's understanding, galaxies are formed primarily by the interaction of gravitational forces of stars and planets, however, ...
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Magnetic flux from maximum induced emf as a function of angular velocity?

I've done an experiment where I have a small rotating coil in a uniform magnetic field and I've measured the induced emf in the rotating coil as a function of time for several different angular ...
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Eddy Currents Confusion

Here is an image of the classic aluminium vane damping setup in which the induced eddy currents oppose the rate of change of flux. That's all intuitive. The confusion I have is why the force caused by ...
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How are the Bloch equations non-linear?

This question is similar to the following, but I have expanded the question moderately: Nonlinearities arising from linear equations The Bloch equations are described by the following vector equation (...
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Can we use Ampere's law to compute the magnetic field inside a cylinder with circular current density?

I am having trouble computing the magnetic field from a cylinder carrying a uniform circular current density j as shown below. My approach was to use Ampere's law, with a rectangular amperian loop ...
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Perfect conductor in a time-dependent magnetic field

I have read about how a perfect conductor responses to a time-dependent magnetic field. It was stated that the "equation of motion" of such a perfect conductor is given by $$\frac{dj(r, t)}{...
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In view of the frozen flux theorem, why don't stars have much stronger magnetic fields?

According to the frozen flux theorem or Alfvén's theorem, the magnetic field in a plasma is frozen into the plasma and must move along with it. That is, in an ideal plasma, the magnetic flux through ...
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Using "Maxwell's curl equations" to get $H_y = \dfrac{j}{\omega \mu} \dfrac{\partial{E_x}}{\partial{z}} = \dfrac{1}{\eta}(E^+ e^{-jkz} - E^- e^{jkz})$

I am currently studying the textbook Microwave Engineering, fourth edition, by David Pozar. Chapter 1.4 THE WAVE EQUATION AND BASIC PLANE WAVE SOLUTIONS says the following: The Helmholtz Equation In ...
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How to find field strength of magnetic field of an oscillating dipole without $x,y,z$ variables?

(For better viewing, visit https://lateral-bathroom-f63.notion.site/How-to-find-field-strength-of-magnetic-field-of-oscillating-dipole-without-x-y-z-variables-ea0d864f371e4649a21d6cf5d007f9ee) I have ...
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Formula for Magnetic Force on a Current-Carrying Wire

There seems to be a pretty standard formula, that if a wire of length $\ell$ carrying current $I$ is immersed in a magnetic field $B$, then the magnitude of the magnetic force is $$F_B = I \ell B sin \...
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