# Tagged Questions

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 ...

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### Switching on a light bulb. Initial EM/electron pulse propagation

TLDR When switching on an electrical device (e.g. a light bulb or a heater), there is an initial wave (pulse) travelling with very high speed (close to the speed of light) and “carrying the ...
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### What force is needed to slide a plate off a magnet?

I have read related the wiki article but I am not able to find a solution to my problem: how to find the min force needed to separate a magnet. I suppose that the force exerted by one magnet is ...
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### Sequential Stern-Gerlach devices - realizable experiment or teaching aid?

At least one textbook [1] uses sequential Stern-Gerlach devices to introduce to students that the components of angular momentum are incompatible observables. Viz., the $z$-up beam from a SG device ...
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### Field of Solenoid

I was reading this, where in the very beginning I stumbled on the "particle in a solenoid field theme". What's written in there is: The potentianl $\textbf{A}$ is chosen to be that of a solenoid ...
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### What will happen to a permanent magnet if we keep the same magnetic poles of two magnets close together for a long time?

What will happen to permanent magnet's magnetic field or magnetic ability if we keep same magnetic poles of two permanent magnet for long time? Will any magnetic loss happen over the long period of ...
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### Force of a solenoid on a ferromagnetic material

As I was trying to find an answer to another problem, I was informed that the equation I was using would not work. The equation I was using was $$F = (NI)^2\mu_0\frac{\text{Area}}{2g^2}$$ If this ...
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### Is the magnetic field zero inside an ideal conductor carrying a current? [duplicate]

By an ideal conductor, I mean one with zero resistance. The question is not about a superconductor. As I know superconductor and conductor with zero resistance are not the same thing. The question ...
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### Applying Ampere's Law for Two Parallel Wires

This seems a simple question but I'm not able to understand it properly. Say we have two parallel wires carrying same current I in different directions. We need to calculate the magnetic field at any ...
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### Can I use an electromagnet as a shark repellent? [on hold]

I scuba dive, and also spearfish. Doing these sports in the ocean presents obvious challenges since Sharks exist in the ocean. I know about a product called shark shield which uses magnetism to ...
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### Mechanical, not voltage driven electron motion creating larger net electromagnetic force

Have mercy I'm a physician not a physicist. Electrons' Motion in an electromagnet is on the order of 10$^{-4}$ m/s. That charge can be mechanically rotated in a capacitor with a million times more ...
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### Is there any example where electric and magnetic fields are not perpendicular?

Perpendicular electric and magnetic field creates light or other electromagnetic waves. Is it a necessary property to have a perpendicular fields? If not what would happen when the fields are not ...
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### Could I make a magnetic foam or film by mixing magnetic dust?

I'm a developer and tinkerer more than an academic, and I'm not sure if this question, being more practical and less theoretical, will be welcome or not here. But here goes, with apologies in advance ...
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### Does removing half of toroidal ferromagnetic core significantly reduce flux density in the remaining half?

Assuming a DC current in a cable has induced a magnetic field around the cable, and a ferromagnetic toroid is used to concentrate the field; if half of the toroid were cut away (so the cable is no ...
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### If magnets exert greater force on heavier objects, why is it possible to separate magnets from very heavy objects?

I was thinking of the question "Do magnets exert more force on heavier (more massive) objects?" I would think the answer is "yes", because for example if you have a magnet and 2 paperclips, they will ...
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### Mag.-flux build up…hate it

"An old bell ringer". After a few minutes of running, the steel pole of transformer, slowely becomes magnitized. Are there any unique metals that would prevent the mag.-flux build up, in the steel ...
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### Why can't weak core-less electromagnets be used in conjunction with strong permanent magnets to perpetually harvest energy?

Why can't weak core-less electromagnets be used in conjunction with strong permanent magnets to perpetually harvest energy? Magnets will attract ferrous materials but some materials like copper or ...
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### When to apply $\frac{mv^2}{r} = q .v .B$

A charged particle of mass $m$ is moving with a speed $u$ in a circle of radius $r$ . If the magnetic field induction at the centre is $B$ and the charge on particle is $q$. I want to know why I can't ...
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### Magnetic fields in transformers and back emf?

i am having some trouble with understanding the magnetic fields inside transformers and how they relate to back emf. My first query is: is the magnetic field produced inside the soft iron core ...
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### Why do magnetic field lines converge where the strength is strongest?

In most of the sites, they just say that "to determine the strength of the magnetic field, one must look at how many lines are present at a particular location." But my question is why? Why is this ...