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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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Where does this form of the induction law come from?

I am currently studying a eddy current disk break and came across this promising paper (PDF, princeton.edu) from 1942. However, in the first formula a suspicious $4\pi$ appears before the current $U(...
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1answer
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Is the magnetic force fully analogous to gravitation?

Superficially, the force between two magnets would seem to be fully analogous to gravity because each is the product of two factors divided by the square of the distance between the objects being ...
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Simple explanation to the induction from the slowly changing $\vec B$ of a solenoid in the region of $0$ magnetic field

I would like to get some elementary intuition into the problem a solenoid fed with a time-dependent current, and the resulting current that such the solenoid field would induce in a loop completely ...
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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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How to determine the best-fit magnetic dipole Gauss coefficient in a shifted coordinate system?

Introduction A planetary magnetic field $\vec{B}$ can be described outside of the planet using Gauss coefficients $g_n^m$ and $h_n^m$ and a spherical harmonic expansion: $$\vec{B} \;=\; -\vec{\...
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1answer
30 views

Field Line Diagram for Small Bar Magnet in a Magnetic Field

I understand the resultant magnetic field diagram produced when a current carrying wire is placed in a magnetic field as shown in the diagram below. However, what would this field diagram look life ...
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1answer
41 views

A particle of mass $m$ released in crossed gravitational and magnetic field [closed]

A particle of mass $m$ and charge $q$ is dropped from a height $h$ (much smaller than radius of earth). In whole space there exists a constant magnetic field in $-z$ direction and gravitational field ...
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1answer
32 views

Is this a correct use of Ampère’s Law?

Here is the derivation (http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/toroid.html) of magnetic field produced by a toroid. He has taken the loop to be a circle, and Ampère’s law says that ...
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1answer
37 views

Magnetic Flux penetrating a closed loop of area A

Consider that we have a wire containing current $I$ and there is a closed square loop of area $A$ and we need to calculate the flux penetrating this loop. First, we know that the field B due to a ...
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3answers
39 views

Why the angular velocity in DC MOTORS = 0 when torque is maximum?

Why the angular velocity in DC MOTORS = 0. when the torque is maximum. is it supposed to be maximum with angular velocity and torque in the same time!
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1answer
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Lorentz force in superposition of two magnetic fields

When an electron with charge $q$ travels with velocity $v$ perpendicular to a magnetic field generated between two permanent magnets with field strength $B$ and no electric field, it experiences a ...
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Lighting an Electric Bulb with Earth's Magnetic Field

Yesterday, I was solving some problems of Electromagnetic Induction. Suddenly a thought struck my mind. Earth has its own magnetic Field.If an aircraft of metallic body is flying in the air then ...
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1answer
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When does magnetic force act as a centripetal force and when doesn't it? [closed]

As the title says, when does magnetic force satisfy $a=v^2/r$? Is it only when the angle between $\vec{B}$ and $\vec{v}$ is $90^{\circ}$? What happens if there's another force acting on the charge? (...
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Magnetic field strength by breaking a bar magnet in half?

So if I’m thinking about a bar magnet with domains, breaking it in half gives it half the domains, so the field strength should be half. But if I were to compare it to something like a solenoid ...
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36 views

How to plot magnetic field lines “MANUALLY”?

We all know that "magnet" are consist of "dipoles". So we can imagine each dipole is a "miniature magnet". So if I want to "plot" the gradient vector of a magnet on certain point. Am I correct to ...
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1answer
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Magnetic Field Gradient of a Ring Magnet

The magnetic field gradient of a ring magnet I could find online is all oriented up and down. Which means the bottom part of the ring is S or N and the top part is the other. For simplicity I made ...
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Magnetic lines magnetic fields [duplicate]

I think I found the magnetic lines in a photo I took myself. Certainly not immediately. When I was editing the picture, I saw some of the figure, and one half of the photo is a mirror image of the ...
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1answer
54 views

Charged particle moving in magnetic field using cylindrical coordinate [closed]

It's knowen that a charged particle take a helix trajectory in a uniform magnetic field $B =B e_z$ I tried to study this problem using cylindrical coordinate and i get that $$F=q v ×B = m a$$ in ...
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39 views

Why does a charged particle experience lorentz force while moving in a uniform magnetic field?

Firstly, when a charged particle moves in an infinite uniform linear magnetic field, it experiences a force.But,how does the charge or how do we differentiate that the relative position of charge is ...
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23 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?
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31 views

Magnetic cage for keeping plasma around itself

Let's assume that we have an object in vacuum, venting hydrogen plasma around itself. This object has a powerful internal electrical source, connected to a cage of superconducting wire around it, in ...
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0answers
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Would a penning trap be disrupted if passed through the Earth's magnetic field?

Working on my essay for school and currently talking about using antimatter as a propulsion technique for rockets. At the moment I am talking about potential hazards and was wondering if passing ...
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1answer
36 views

Why does a charge moving parallel to the direction of magnetic field experience no force at all?

I can do the math using Lorentz force equation and it turns out that the angle is $0$. I understand that the magnetic field lines of force generated by the charge will be circular and perpendicular to ...
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2answers
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How to visualize the merge of magnetic field?

Magnetic fields are represented by field lines and it is stated that these lines are closed lines, going through the source (often shown as lines between the two poles of the source). Approaching two ...
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1answer
44 views

What electric and magnetic field lines look like in some examples?

I have seen this but couldn't understand so I wrote my own question. We all have learnt in school that electric field lines never intersect. Same is the case for magnetic field lines. But I have a ...
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0answers
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Permeability measurement of free space

My question is related to the question recently asked in Lenz's law and the motor effect For case 2, if we know the current in the wire and measure the force exerted downwards, the field between ...
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1answer
21 views

Magnetic fluxdensity

Suppose a magnetic field with field lines pointing downwards and a conductor shaped as a loop that conducts a current. The conductor is static, and is placed half in the magnetic field. Is there a ...
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1answer
46 views

Converting normal water into magnetic water [closed]

When I magnetize water by circular magnets of strength 0.8 T, how long will the magnetism be present in the water? I mean, how many days will it be in the water?
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1answer
28 views

Why is the direction of current in a wire different depending on if a force induced a current or a current induced a force?

In school we are taught about the motor effect and the dynamo effect. We are also taught Fleming's left-hand rule and Fleming's right-hand rule to describe the motor effect and dynamo effect (...
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1answer
25 views

What is the position of neutral point when a bar magnet is placed facing N-pole eastward?

when a bar magnet is place N-pole facing geographical North, the neutral point is obtained on axial line. Where will be the neutral point when it is rotated so that N-pole faces geographical east?
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How can one generate a magnetic field of a specific intensity(in terms of flux)?

Was wondering how to generate a static magnetic field of a fairly precise value(teslas) for my science class. It needs to be relatively precise. Thanks for the help you can offer.
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Current density on Perfect Magnetic Conductor

I know that PMC boundary condition requires tangential magnetic fields to be 0. I also learned that PMC condition requires tangential current density to be 0. Is this condition a result of 0 ...
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3answers
86 views

Lenz's law and the motor effect

The picture shows the basic motor effect, which can be described with Fleming's left-hand rule. There are two cases of what could be happening however. Case 1: There is a force applied to a wire such ...
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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 ...
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Magnetic field of solenoid from superposition of loops [closed]

I was thinking if it could it be possible to calculate the field inside a solenoid $$B = \mu_0 n I$$ using the principle of superposition for the magnetic field for $N$ circular loops centered on the ...
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Gauss measurement at specific point within a magnetic field?

I am reviewing specifications from a manufacturer that produces a cryogenic electromagnet. Their specification indicates that the stray magnetic field is much higher on the x axis than y or z. At 2m ...
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1answer
36 views

A circularly charged insulating disk rotates

A circularly charged insulating disk rotates around its axis. Why is there a magnetic field around the rotating disc?
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response to magnetic field is smaller than electric field?

I'm reading a paper, which just explain an another approach to derive Fresnel's equation. (https://aapt.scitation.org/doi/pdf/10.1119/1.15551?class=pdf) At one point, it says One naturally asks ...
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Lateral force of electromagnets

I have a project that entails finding the equation for the force of electromagnets laterally for a distance apart. I was able to find an equation from this research paper: http://www.jpier.org/PIERB/...
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3answers
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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 ...
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1answer
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Force on current carrying wire in magnetic field

I was doing an experiment on the force on a current carrying wire in a magnetic field. I used an electric weight to register the magnetic force. When I used the force, current, and length of the wire ...
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1answer
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Force on current carrying conductor

I got this question from a talent search examination. I checked the answer keys and i had got it wrong. The answer is option D. From the formula, F = BIL, force is directly proportional to the ...
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1answer
35 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 ...
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1answer
70 views

I have a pair of magnets that when I let go they attracted and broke

I let two magnets attract from a distance and when they hit they both broke a piece off of each-other. Why did the magnets damage each-other when they collided and is it possible to put the broken ...
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Is Coriolis force necessary for geomagnetism

I understand that the Coriolis force from the earth rotation organizes the current flow in the earth outer core into columns of rotation the axis of which parallel the earth rotation axis. That ...
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1answer
34 views

Ampere's law for a loop with zero enclosed current [duplicate]

Imagine a wire with current I flowing through it. If we take a closed loop that doesnt contain the I the line integral will be zero. Does this means magnetic field is zero ? Also does Ampere law ...
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1answer
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Do plasmas really not experience a $\nabla \vec B$ drift even though the individual particles do?

I'm currently working through Chen's Introduction to Plasma Physics and Controlled Fusion, and I just got to the chapter on the fluid theory of plasmas. Chen claims that the $\nabla\vec B$ drift does ...
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Can torque in a brushless DC motor be analyzed using Lorentz force law?

Torque in a simple brushed DC motor can be analyzed using Lorentz force law. It also turns out that the torque on the magnetic dipole generated by the rotating wire loop is the same as the torque ...
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4answers
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How does a magnetic field interact with a moving charged particle?

It is known from $\mathbf F = q(\mathbf v \times \mathbf B)$ (magnetic part of Lorentz force law) how a magnetic field interacts with a moving charged particle. Without going too deep into the matter,...
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Force felt by a moving charge due to its own magnetic field?

Suppose a moving proton traverses a uniform magnetic field with constant velocity. Note that because the proton is moving, it is generating its own magnetic field. Is the magnetic force experienced ...