# 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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### Being the Earth modelized as a big magnet (or solenoid), which would be the field intensity of such a model inside the solenoid or magnet axis?

This question has arisen from the Carl Friedrich Gauss’ statement that the Earth could be modeled, concerning his calculations about the earth’s magnetic potential, as a big magnet, himself having ...
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### What is magnetostatic energy?

Sometimes, it becomes extremely difficult to visualise the physical significance of a given term only by its definition. I have been facing trouble understanding what exactly magnetostatic energy is? ...
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### Electromagnetism Physic [closed]

Hiii guys please help me. The question is that Mary and her friends are camping in Kuala Woh. While they are hiking in the jungle, they lost their way. They have a compass but the marking on it has ...
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### Magnetic field generated by a wire crossed by current: clarifications

We know that from Oersted's experience the lines of force of the magnetic field generated by a wire crossed by current $I$, are concentric circumferences of radius $r$ (variable) where the centre is a ...
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### What does direction of EMF mean?

In faraday's law it mention's direction of EMF( like in closed loopit is clockwise or anticlockwise depending on direction of motion of magnet) but defination of EMF is roughly Potential diffrence ...
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### Particle deflection in a magnetic dipole field

Consider a small magnetic dipole of magnetic moment $\vec{\boldsymbol{\mu}} = (\mu_x, \; \mu_y, \; \mu_z)$ sitting at the origin. The magnetic field all around is \begin{equation}\tag{1} \mathbf{B} = ...
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### Does magnetic field make particle move in the direction of magnetic field(In circles)?

So my task says A particle with mass $m$ moves freely through space and there is no electromagnetic field. At moment $t = 0$ a uniform magnetic field is turned on with field strength $B$, and ...
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### How to calculate surface current density

So I have the question where you have an infinitely long cylinder, with $\vec{B}(r)=\frac{B_{0} r}{R} \vec{e}_{\varphi}$. Then with $\oint \vec{B} \cdot \overrightarrow{d l}=\mu_{0} I_{e n c l}$, with ...
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### Converting from magnetic scalar potential to magnetic vector potential

Suppose that I have a situation where I can use the magnetic scalar potential. Given the magnetic scalar potential, is there a simple way to calculate the magnetic vector potential from the magnetic ...
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### What's the difference between the north and the south pole on a magnet?

I was testing out objects with magnets and I didn't understand what made the north pole different from the south pole. I thought the poles were made of different materials, but I realized it wasn't. ...
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### Magnetic force on current carrying wire

when we keep two wires near each other then they will experience same force is it then correct to explain by newton's 3rd law? -
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### AC wire radiation

I'm trying to test my recently installed MEEP program for a very simple AC current. I know that for DC current, Ampere's law dictates that the magnetic fields must drop off as 1/r. How does this ...
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### Contradicting forces on a circular loop under current in magnetic field?

I have the following general conceptual concern. Think of a thin conducting loop of radius $R$ placed in the $x$-$y$-plane at $z=0$. There is a homogeneous current density $\vec{j}$ running through ...
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### An electron moving through a magnetic field [closed]

An electron, that has been accelerated from rest by a potential difference of $250\ \rm V$, enters a region of magnetic field of strength $0.12\ \rm T$. Show that speed of the electron after ...
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### Curl of magnetic field ( Ampère's law)

I'm a little bit confused about Ampère's law concerning the curl of a magnetic field: $$\vec{\nabla}\times\vec{B}(\vec{r}) = \mu_{0}\vec{J}(\vec{r})$$ with $\vec{J}(\vec{r})$ the volume current ...
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### Is there an effect of magnetic field on stationary charge

Why does a magnetic field only exert a force on moving charges and not on stationary charges as electric field does?
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### How can a refrigerator magnet be stronger than the Earth's magnetic field?

This Wikipedia page lists examples of magnets and magnetic fields of different strengths. I don't understand why it claims that the Earth's magnetic field is less strong (31.869 µT) than a ...
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### Magnetic Hysteresis: How is magnetization not zero when magnetic intensity is zero?

We know that, $$M=\chi H$$ So from this relation when H(magnetic intensity) is 0, M(magnetization) must also be 0. But this is not the case. Could someone please explain this to me in simple terms, ...
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### What is the speed of the magnetic field?

There is an invisible magnetic field that pushes apart two repelling magnets What is the speed of that magnetic field?
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### Net magnetic field in various cases and if they're same

Recently I've begun to study magnetism and I'm familiar with the fact that all wires (however ideal they may be) will have a magnetic field around them when they have current passing through them and ...
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### How do magnetic field lines cancel outside of a solenoid?

Please explain me briefly, how magnetic field lines cancel outside solenoid? There is only one wire wrapping it and therefore only one direction of current so how can magnetic field cancel out? How ...
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### Magnetic Properties under Pulsed Power

If one were to apply 50 kV at 17 A with a pulse width of 100 microseconds and a frequency of 10 Hz across a samarium cobalt magnet, would the magnet reach its Curie temperature during the time when ...
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### Direction of integration and boundary limits in electromagnetism?

I have encountered several problems regarding the choice of direction of integration and the boundary limits, this semester in electromagnetism. Is there some rule, so I don't do it wrong again. In ...
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### Why shouldn't I choose my boundary limits corresponding to the direction I'm integrating?

I have a question regarding the choice of boundary limits when it comes to vector integrals. Why shouldn't I always choose the boundary limits corresponding to the direction I'm integrating. I.e why ...
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### Ferromagnetism and induced magnetism

According to Wikipedia: A magnetic domain is a region within a magnetic material where individual magnetic moments of the atoms are aligned with one another and point in the same direction thus ...
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### 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 ...
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### Can a magnetically levitating sphere spin in any direction?

I am trying to design a system that levitates a sphere (ball). I have found several solutions, however, it seems to me that the levitating ball only has one degree of freedom, i.e. rotation around the ...
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### Localized and extended states in Landau levels due to disorder in Integer Quantum Hall Effect

In the presence of a random potential due to the presence of disorder, the degenerate Landau levels split into a band. It is given that the states in the middle of this band are extended and the ones ...
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### Symmetry arguments in Magnetostatics

I am not sure that I understand how to argue using symmetry arguments that the magnetic field lies in a certain direction. Say we are given a circular loop of radius $R$ with a steady current $I$ ...
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### EMF in an Open circuit?

If a wire that is connected to a circuit passes a magnetic field, it would induce $EMF$ that would allow current to flow, and generate an opposing force. Now what if the wire is not connected to a ...
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### Magnetic field like phenomenon associated with Gravitational Field [duplicate]

Like in electrodynamics we have magnetic fields associated with electric fields, is there something similar related with gravitational fields too? I mean both are quite similar fields...(Maybe I'm ...
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### 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 ...
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### Magnetic field on a super conductor cylinder

Suppose that i have a cylinder of the z axis. I'll put this cylinder on a uniform magnetic field with magnitude of B0 along de y axis. Since we have B = 0 inside the superconductor, this will ...
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### Can non-conservative field store energy when work is done?

Taking a non-conservative field like magnetic field (in presence of current density), when work is done can it store energy? If so how?
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### Magnet spinning between two other magnets

Suppose, we have two magnets, MA, MB, and we have a third magnet MC in between the two magnets. Each magnets' north pole faces the other magnets south pole, and the magnets are placed horizontally ...
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### Materials/Objects that only create soft iron distortion and hard iron distortion to a magnetometer respectively?

Does it exist a material or object that only produces soft iron distortion - without hard iron distortion? And does it exists a material or object that only produces hard iron distortion - without ...
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### Magnetic force between broken magnetic circuit

The above image shows the flux flow through a rectangular core. We know the purpose of the core is to concentrate as much of the flux through it as possible, so we'll assume no or minimal stray field ...
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### Velocity Selector Question with Unknown Voltage

In a diagram, electrons are emitted from a hot coil with initial velocity 0 at plate A and then pass through a uniform field between two plates (A and B) where $V=1.00\times10^4$ volts. After, they ...
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### What are some examples of magnetocaloric materials?

I've recently become fascinated with a cryo cooling method known as "magnetic refrigeration". Here is the Wikipedia article. I was wondering if there is a list of magnetocaloric materials. ...
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### demagnetizing a magnet

This is a theoretical question. Some elements described in the problem may be impossible/impractical, but I am just trying to understand the principles. Suppose I have a powerful electromagnet with ...
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### Magnetism in different reference frames

Moving electric charges produce magnetic fields. As explained in this great Physics.StackExchange answer, we can think of magnetism as simply electrostatics combined with special relativity. My ...
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### How does one calculate the force applied on an object by a magnetic field?

I've tried very hard to find an answer to this question, and every path leads me to an abstract discussion of fundamental forces. Therefore, I will propose two very specific scenarios and see if they ...