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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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Physical Relation in Maxwells Equations of quantity between as well as fundamental forces

Recently learnt about Maxwells Equations, am wondering what is the physical relation between electric field E and magnetic field B. It would help if the physical meanings are related to the ...
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1answer
46 views

Can someone explain how magnetic potential energy can exist even though the field is non-conservative?

$U=-B\cdot \mu$ is defined to be the magnetic potential energy, I saw this in my lecture notes, but we had already talked about the fact that since the work done to move a charge there is path ...
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1answer
50 views

Is it true that you can block a magnetic field?

So as the Avengers 4 comes to the movie theater, Thor's hammer is getting popular around the market, where I found one product that claims can stick on a metal surface tightly when wanted. Apparently, ...
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2answers
36 views

Vector potential of magnetic monopole

I am following the step on this introduction to magnetic monopole. I understand that the vector potential produced by semi-infinite solenoid is exactly the vector potential of magnetic monopole. But ...
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0answers
10 views

Capacitance of Three Metalic Cylinders [on hold]

Three concentric, thin, long conducting cylindrical shells have radii of 12, 47, and 137 [cm]. The space between the shells is filled with air. The innermost and outermost cylinders are connected at ...
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1answer
12 views

Effect of the magnetic field of a moving charge on the magnetic field used to accelerate the charge

Ok, so my brief understanding is that an accelerating charge will produce a magnetic field. If the charged particle, say an electron is being accelerated by a magnetic field, how does the electron’s ...
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0answers
9 views

Eddy Current Pendulum and Variables of Breaking Force

I am trying to conduct an experiment about eddy currents, specifically using an aluminum plate pendulum, two permanent magnets, high framerate camera. I am altering the distance between the two ...
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0answers
25 views

Query about why there is a torque on this spinning ring in a magnetic field

We learnt in class that the $\vec m\times \vec B$ is the torque of a current loop in a magnetic field. I was trying to understand this by considering the diagram above. Let the B field be pointing in ...
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4answers
88 views

Can every mass obey the Newton's 3rd law?

As in, if we were able to produce a very huge amount of force on a very small body, would it push back with the same force? Given it doesn't break or disintegrate. Like if we electromagnetically put ...
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1answer
39 views

What speed does the particle leave the magnetic field given its circular path radius?

I've attached the question as an image below as it's a graphical question. It simply states: "Different magnetic fields are present in the two chambers shown. A particle enters the first chamber at ...
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1answer
36 views

How to calculate spherical coordinate components of dipole field?

I understand well enough how to calculate the radial and tangential components in spherical coordinates at a point due to a magnetic dipole field using the magnetic potential gradient ($\...
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1answer
23 views

Permeability constant in Ampère's circuital law must be vacuum permeability $\mu_0$?

Just to be sure, is the permeability constant in Ampère's circuital law always equal to $\mu_0$, regardless of which medium the Amperian loop is placed in? That is, $\oint {\bf B} \cdot d {\bf \ell} = ...
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1answer
24 views

Why use vacuum permeability during derivation of $\vec{B}=\mu_0(\vec{H} + \vec{M})$

Why do we use $\mu_0$ during the derivation of $\vec{B}=\mu_0(\vec{H} + \vec{M})$ where $\vec{M}$ is magnetization? The derivation given in Sadiku's Elements of Electromagnetics: Let $\vec{J_f}$ be ...
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1answer
22 views

diffusion of magnetic field and Joule heating effects

Since the magnetic induction equation is $${\frac {\partial {\boldsymbol {B}}}{\partial t}}=\nabla \times ({\boldsymbol {v}}\times {\boldsymbol {B}})+\eta \nabla ^{2}{\boldsymbol {B}}$$ I want to ...
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2answers
69 views

Why are fridge doors magnetic?

Why do fridge magnets stick to fridges? What purpose does a magnet have in a fridge? Why do the magnets stick so well to the fridge doors but not so well to keys or nails?
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0answers
24 views

How do I find the magnitude and direction of the magnetic field of a permanent magnet at an arbitrary point using physics equations?

I've been wanting to do some simulations on my computer that illustrate the magnetic field of a magnet. I have quite a few .5/.5/.5" cubic neodymium magnets and have been arranging them together to ...
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0answers
27 views

Conservation of Energy Issues When Considering Permanent Magnets on Flywheels [closed]

I am trying to determine how to deal with magnetic potential energy in a Conservation of Energy analysis. Consider an asymmetric permanent magnet with strongest field on north pole mounted on a very ...
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5answers
829 views

Cross products/avoiding using your hand for the right hand rule in E and M

I am currently learning electromagnetism and I am getting really annoyed using a physical hand to accomplish the right hand rule. I get it, i've seen diagrams, and i've solved problems with it but ...
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0answers
31 views

Please clarify a doubt in the article: Reflections in Maxwell's treatise

While going through an article titled "Reflections in Maxwell's treatise" a misunderstanding popped out at page 227 and 228. Consider the following equations $(23\ a)$ and $(23\ c)$ in the article (...
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0answers
16 views

The issues when thinking about the magnetic flux law as being universal in modeling

$$ \varepsilon = -\frac{\partial \Phi}{\partial t} =-\frac{\partial (BA)}{\partial t} $$ Any instance of considering the emf induced in a system, I usually think of the flux law first, I intensely ...
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0answers
13 views

Magnetic field from a current arc and its limiting behaviour

For my sanity and the sake of book keeping, I have been going over the very well known and documented calculation for the magnetic field of a current loop. I have been trying to verify the limit ...
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0answers
19 views

How to keep a particle moving in a magnetic field in the horizontal direction?

A particle of mass $0.5 $ g carries a charge of $2.5\times 10^{-8}$ C. The particle is given an initial velocity of $6 \times 10^4$ m$\cdot$s$^{-1}$. To keep the particle moving in a horizontal ...
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1answer
29 views

Magnetic field due to a circular ring

In the EMFT notes of MIT Course-ware, the derivation of the magnetic field due to a circular ring at its axis, using Biot-Savart's Law and the cylindrical coordinate system is done as follows, I am ...
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1answer
32 views

How cavity magnetron works?

I've found an explanation on explainthatstuff.com. There are these electrons from the cathode that are going around in a circle (because of the magnetic field), passing next to the cavities. Then it ...
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0answers
37 views

How is the rotation of a ferromagnetic bullet affected by a coilgun?

I've been asked a question that I'm unable to answer. It's about a coilgun, and even if it could probably be expressed in simpler terms, I'll ask it in its entirety just in case I make mistakes while ...
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1answer
28 views

What are the best substances for use in magnetic shielding? [closed]

I've recently become interested in magnetism and have bought a few cubic neodymium magnets to play with. I'd like to find a substance (not another magnet!) that shields against a magnetic field. I'm ...
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0answers
16 views

Finding Line Integral Of Magnetic Field over Quarter Circle

This is one of the question in my workbook and I tried solving it in above way. However I am not able to get the answer. Can anyone suggest a method to solve this question ? Am I doing a mistake in ...
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1answer
26 views

Relationship between the: Power supply's electric force for current flow, and Lorentz force equation for electric force?

$$ F = qE + qv \times B$$ For the Lorentz force relevant to a current carrying wire, that is caused by the motion of a wire w.r.t to an exterior magnetic field $B$, the second term($qv \times B$) on ...
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1answer
82 views

Does a homogeneous oscillating electric field produce a magnetic field?

I am working on a homework problem that says an electron in a continuous laser field can be modeled as experiencing a homogeneous oscillating electric field $\vec{E}(\vec{r},t)=\cos \omega t \ \hat {z}...
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1answer
33 views

Detect compass disturbance

I am looking for a way to determine wether the compass of a phone is showing inaccurate north heading by looking at magnetometer values. Right now I have been looking at total magnetic field ...
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0answers
53 views

Is the speed of Magnetic field infinite?

My real question is: From Amperes law we know that there is no magnetic field outside of the coaxial cable because the magnetic field generated by the inner wire and outer shell are equal but in ...
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1answer
31 views

Will a led, connected to a long conducting rod, shine when the rod is falling through the magnetic field of the Earth?

Visualize a long conducting rod of length $l$ falling towards the Earth (after being released from a hight of say $5(km)$) perpendicularly to the Earth's magnetic field. Near the earth's equator, ...
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0answers
26 views

How much energy does it take to magnetize a neodymium magnet?

I read somewhere that when neodymium magnets are made they are subjected to intense magnetic fields in order to magnetize them. So lets say we have a cubic neodymium magnet that is .5 by .5 by .5 ...
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1answer
27 views

Magnetic Circuits: Why is magnetic Flux constant through one loop of a magnetic Circuit?

Wikipedia states that for a magnetic circuit, the magnetic flux throughout the path of the circuit is constant. If I understand right, this means that \begin{align} \Phi_1 = \Phi_2 = \Phi_3 = \Phi_4 =...
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1answer
24 views

Force on Magnetic Dipole - Equivalent Formulas?

I have seen two different ways of expressing the magnetic force on a dipole moment in a non-uniform magnetic field: $\vec{F_a}=(\vec{m}\cdot\nabla)\vec{B}$ or $\vec{F_b}=\nabla(\vec{m}\cdot \vec{B})$ ...
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2answers
36 views

Magnetic field at boundary of electromagnet iron core

Assume you have an iron core in the interior of the solenoid. It is well known that the strength of the field should increase by a factor of several hundred inside the solenoid as a result of the ...
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0answers
10 views

Resources for spin-stabilized magnets

I will be carrying out an experiment investigating the factors that effect the speed of a spin stabilized magnet. Can someone provide resources or articles that talk about/ have formulas related to ...
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0answers
17 views

Ion separation is effected by static or dynamic electric or magnetic fields?

My textbook says the following: The basic principle of mass spectrometry (MS) is to generate ions from either inorganic or organic compounds by any suitable method, to separate these ions by their ...
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0answers
19 views

Relation between: density/twisted-ness of magnetic field lines and energy stored in the magnetic field

I am having difficulty reconcile the following two "intuition"s: The denser the magnetic field is, the more energy it stores. we have seen many equations calculating flux involving B. For Example: ...
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0answers
19 views

Regarding induced magnetic field due to changing electric field

I am trying to solve this question: My approach was to first notice that the electric field is decreasing, therefore the change in electric field is to the left. If I point my thumb in the direction ...
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1answer
22 views

How can I calculate magnetic field strength from latitude longitude?

How can I calculate magnetic field strength from any given latitude longitude?
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0answers
28 views

Magnetic quadrupole and dipole

We can create a quadrupole magnetic field disposing magnetic dipole as in this figure I have two question about this: How can I write the quadrupole moment in terms of the dipole?; Is it correct to ...
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1answer
17 views

Net bound current with uniform magnetization

My confusion stems from the following: Can I reason the answer being (D) analogous to... for instance: If this was instead a solid cylinder with uniform polarization $\mathbf P$ pointing in the z-...
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1answer
38 views

Inconsistencies in finding magnetic vector potentials

Recently I've been studying for my electromagnetism finals and I reached a question about magnetic vector potentials. If I have a wire with constant current distribution, what is the magnetic vector ...
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2answers
33 views

Why does the electric field and not the magnetic field remains in the same direction after reflection from a medium?

I was reading up about reflection and transmission when an electromagnetic wave is normally incident on a surface. I came across this figure : My question is why is the direction of electric field ...
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1answer
27 views

Magnetic flux density compard to other definition of flux

With regards to flux i have always assumed it was defined as $$(1) Something/m^2s$$ For instance $Luminosity/(4\pi r^2)$ Is an example of radiation flux. Why then is faradys law often cited as the ...
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5answers
69 views

Is tangential component of $\mathbf{B}$ undefined at the boundary of two media?

Tangential component of $\mathbf{B}$ is discontinuous at the boundary of two media. Does this mean that tangential component of $\mathbf{B}$ is undefined at the boundary of two media? If yes, then: $...
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0answers
36 views

Doubt on why magnetic flux density is solenoidal

The $\mathbf{H}$ field can be derived from the potential $\psi$: $$\mathbf{H}=\dfrac{\mu_0}{4 \pi} \int_{V'} \rho \dfrac{\mathbf{r}-\mathbf{r'}}{|\mathbf{r}-\mathbf{r'}|^3} dV' + \dfrac{\mu_0}{4 \pi}...
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1answer
664 views

Size of electromagnet needed to replicate Earth's magnetic field

I guess the title says it all. How big of an electromagnet would you need to generate a magnetic field the same as Earth's? Like, what kind of amperes are we talking here? (Assuming a hypothetical ...
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3answers
169 views

Quantum Hall Effect: Why the spikes of the longitudinal resistance appear every time when Hall conductance jumps?

[ Let's focus on the longitudinal resistance, I have two confusions: Why it shows spike like feature every time the hall conductance jumps? Why its amplitude grows when the magnetic field grows? ...