# 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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### 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 ...
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 ...
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 ...
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 ...
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 ...
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. ...
1answer
60 views

0answers
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### 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{...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
2answers
122 views

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 ...
2answers
39 views