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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2answers
686 views

Why is the divergence of a magnetic field equal to zero?

We know due to Maxwell's equations that: $$\vec{\nabla} \cdot \vec{B}=0$$ But if we get far from the magnetic field, shouldn't it be weaker? Shouldn't the divergence of the field be positive? If ...
4
votes
2answers
65 views

Why does an electric motor burn up when you physically stop it?

As an electric motor spins, the energy from the electricity is 'conducted' to the rotor by the magnetic fields. However, when the motor is stopped, the energy becomes heat and burns up to motor. ...
2
votes
1answer
21 views

Are Verdet Constants Temperature Dependent?

The Verdet constant of a magneto-optical material shows up in the calculation of the rotation of polarized light in a medium submerged in a magnetic field. The amount of rotation is given by $$ ...
0
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0answers
20 views

What's the proof that the polarization occur s to the electric field of the light? [duplicate]

What's the proof of the light polarization that it happens to the electric field and not the magnetic field? How did Malus discover that the light is polarized although he didn't see the waves ...
3
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1answer
59 views

How is earth a magnet while it's volume is mostly above curie temperature?

I was assuming the earth's magnetism is similar to a permanent magnet; But below a depth of somewhere near the Mohorovičić discontinuity (Moho) between earth's crust and mantle it should be above ...
0
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2answers
49 views

Condition for the magnetic field

Let $B$ be the magnetic field. If $$\nabla \times B = 0$$ and of course $$\nabla \cdot B= 0$$ Can we conclude that $B=0$? For a general field it is wrong because every constant vector will ...
1
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2answers
109 views

How electromagnetic fields travel through vacuum?

How electromagnetic fields travel through vacuum is it right to say that they propagate or travel? do they alternately form each other by charged particles?
1
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1answer
83 views

What is the outcome of a changing Magnetic Field?

The question might sound elementary. However, the thing is this. Changing Magnetic field produces a changing electric field. That changing electric field would produce a changing magnetic field. So, ...
0
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1answer
52 views

Thomson's jumping ring experiment

For the jumping ring experiment (I think it is also called Thomson ring experiment) why does the ring float and not move up and down the ring as would be expected, I think by Lenz's law, since would ...
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2answers
34 views

Gauss' Law for Magnetism Derivative Form: With or without volume integral?

I've been reading through FLP Vol. II, and he has proven that as the flux through a closed surface is: $\ \int_{surface} \mathbf{F} \space \mathrm{d}\mathbf{a} $, according to the divergence theorem, ...
1
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2answers
71 views

Lorentz force, must there be two magnets?

The diagram above demonstrates the Lorentz force, Yet I wonder... must there be two magnets/electromagnets? If the two magnets form a magnetic field of $1$ $Tesla$ acting on the wire, why not use 1 ...
1
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1answer
20 views

Lamination on a conductor?

How can lamination help reduce eddy currents? I understood that it reduces them, by making their circulation incomplete, or something like that. Can anyone explain this please?
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0answers
5 views

why field cooling is necessary in Exchange bias?

Why is field cooling necessary for exchange bias? For instance, if we take an example of Ni/NiO, in this sample NiO is already anti-ferromagnetic in nature at room temperature. And as we know that ...
2
votes
2answers
47 views

force on a moving charge in magnetic field

Need help in understanding the direction of magnetic force in the magnetic field!Totally confused by directions. Why is it that magnetic force is perpendicular to the direction of magnetic field and ...
0
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2answers
30 views

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 ...
1
vote
2answers
40 views

Magnetic field by a solenoid?

I am really not able to understand why is it that the current,while finding the magnetic field in the solenoid (ideal one), is not I the current flowing throught the solenoid but nI,where n is the ...
2
votes
1answer
49 views

How fast does it take to create a magnetic field in a solenoid?

If a solenoid/electromagnet has current flowing, it creates a magnetic field. Electricity is very very fast, I believe close to the speed of light? So, when power is given to a solenoid with $n$ ...
0
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0answers
23 views

Can a magnetic field alone be used to move a metallic object within a contained tube?

Is it possible to make a metallic object move in a circular contained tube around and around in which a magnetic field is setup to cause the metallic object to move through the electric field within ...
1
vote
1answer
19 views

Can a magnetic field hold a state of supercavitation if a magnetic field could be placed inside of the bubble of the supercavitation?

I have a question that I am just curious about. Two principles: Magnetic fields and Magnetic susceptibility Supercavitation is the use of cavitation effects to create a bubble of gas inside a ...
2
votes
1answer
46 views

Magnetic Fields in water

I have a question for all of the persons talking about magnetism. What are the differences in any of the properties, laws, etc. of a magnetic field totally submerged in water compared to a magnetic ...
1
vote
1answer
53 views

Transformer and magnetic field/flux through the iron core?

I am familiar with how a transformer works. This is the diagram that I found on the wikipedia page: The current through the red solenoid varies with time, which creates a time-dependent magnetic ...
0
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0answers
19 views

What equation should be used when this conductor passes a magnetic field?

A large thick copper wire(or bar if you like,) passes a magnetic field. What formula is best to calculate the $EMF$ here? $$\epsilon = \frac{\Delta \Phi \ }{\Delta t} $$ or, $$\epsilon = ...
2
votes
3answers
84 views

Explanation of Lorentz-Force

In high-school level books (for example the german standard text: "Dorn-Bader") I have often seen an explanation of the Lorentz force as on the following picture: The textbooks consider the ...
1
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0answers
23 views

Magnetic flux and transformers

I have two linked quesitons, 1. what is magnetic flux linkage's formal definitaiton and 2. when people say the flux flows better thru a soft iron core then the air what do they mean by flux flowing ...
2
votes
1answer
68 views

Motional EMF and EMF?

What is the difference between motional EMF = $-vBL$ , and Faraday's law of induction $\displaystyle\mathcal{E} = \left|\frac{d\Phi_B}{dt}\right|$? Aren't they the same? What is the relation of ...
2
votes
0answers
55 views

What happens to the bar magnet field when it breaks?

References says alignment of a magnetic field of a bar magnet remains same even if we cut it into two or more pieces. According to this cut edges should attract with each other. When I tried it was ...
1
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1answer
41 views

Equation for magnetic field due to a current in straight wire [closed]

How can I derive the expression for the magnetic field due to a long straight current carrying wire using the Biot-Savart law? The final expression should be: ...
1
vote
1answer
90 views

How fast does current flow? And the magnetic field? [closed]

A conductor carries 10 Amps, and generates a magnetic field $B$. How fast does it take for that current to flow from the wire throughout the entire circuit? And how fast does it take for the ...
0
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0answers
14 views

The Magnetic Field around the Proton Beams in the LHC

How would one most appropriately model the magnetic field around each bunch of protons in the LHC at maximum operating speed? Is the assumption of a wire of the same length of the beams (~30cm) with ...
7
votes
3answers
2k views

Why is my restaurant silverware magnetized? [closed]

Why is my restaurant silverware magnetized? Specifically, if I lay all three flat on the table, and touch the bottoms of the handles together, I can pull the knife with the handle of the spoon. I ...
1
vote
0answers
61 views

Currents and magnetic fields produce forces that affect things they're not touching?

I was doing this past paper and am a little confused by question 5) part c)ii) I correctly calculated that the force acting on the rod due to the magnetic field is 0.016N but I can't see how ...
1
vote
1answer
40 views

Why is the geomagnetic north pole at a different location from the magnetic north pole?

According to this site Magnetic North, Geomagnetic and Magnetic Poles The Geomagnetic poles (dipole poles) are the intersections of the Earth's surface and the axis of a bar magnet hypothetically ...
1
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1answer
26 views

What gives Maglev trains forward horizontal motion?

Maglev trains have superconductors which are immune to magnetic field lines with low enough temperature. Due to this property, they levitate on magnetic rails as magnetic field lines are bended below ...
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0answers
27 views

EMF & Magnetic force at the same time?

A conductor is placed in a magnetic field, current starts to flow, and the wire experiences the Lorentz force of $x$ Newtons. However, what confuses me is that $x$ is a value that is calculated from ...
0
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0answers
50 views

how do I calculate the B field (strength and direction) on a point charge due to a permanent magnet

I am trying to create a simple 2D Simulation of magnetic fields similar to this; showing the field lines or the effect of permanent magnets. I keep coming across equations like this: ...
0
votes
1answer
39 views

Magnetic Attraction in Space [closed]

If I were to attach a 1 inch diameter magnet to lets say a half pipe, that it fits perfectly in, and attach a 1 in diameter piece of iron close enough for the magnet to assert its attractive pull, ...
0
votes
0answers
31 views

Magnetic field of a wire with over 1000 amperes? [duplicate]

Does a large thick wire that has over 1000 amperes of current flowing through it generate powerful magnetic fields? What formula is best here to predict $B$?
0
votes
1answer
59 views

Magnetic Shielding?

Can magnetic fields be "blocked"? For example, in the game, TitanFall, a robot stop bullets with ( presumably ) a magnetic shield. I wish to calculate the magnetic force required to stop a bullet ...
0
votes
1answer
50 views

How does this particle behave in the magnetic field?

I have the above question and I have though about it every way and can't seem to find out. So what I have concluded (ignore the answers on the img) Is that the force is on the z axis because the ...
0
votes
0answers
31 views

Field outside a solenoid?

Say you have a solenoid with diameter $d$ and length $L$. How can I show that as $d/L$ approaches 0, the field outside the solenoid is zero? I'm looking for a formal proof involving integration. ...
4
votes
1answer
76 views

Poynting theorem and entering power

I refer to the time-domain version of the Poyinting theorem in electro-magnetism: $- \displaystyle \oint_S (\mathbf{E} \times \mathbf{H}) \cdot d\mathbf{S} - \int_V \mathbf{E} \cdot \mathbf{J}_i \ dV ...
0
votes
1answer
53 views

Current vs Voltage Drive for Loudspeakers [closed]

Please see this article: here I don't know enough EMFT to comment on this but I am working on other tasks for a wireless speaker system prototype called "Busker's Friend". Completing my Schaum's ...
1
vote
1answer
55 views

Understanding fields and their correlation to forces

I seem to be confused between the concept of a "force", and a field. Now let's assume there is a magnetic field of $1$ $\mathrm{Tesla}$, what does that mean in relation to force? Finally, if field is ...
1
vote
1answer
35 views

Saturation of an iron core?

Lets assume we have a 1 kg iron core, and a 100 kg iron core. Now saturation is defined as how much that core can absorb the magnetic field, since they are different sizes, don't they saturate at ...
1
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0answers
58 views

Magnetic monopole

I've been watching a lot of videos claiming to make monopoles either by dropping the temperature to 5k (-268° C) and splitting the magnet or by pouring molten metal through an induction system and was ...
0
votes
1answer
60 views

Force from solenoid

I'd like to approximate the force from a solenoid, or at the very least find a formula which is proportional to the force so that I can experimentally find the constant for my particular case. ...
1
vote
1answer
100 views

Is it possible to detect fake Tungsten aka Wolfram gold bars with a strong magnet?

Tungsten aka Wolfram is paramagnetic so it is weakly attracted to magnets. A guy devised the following to test for Tungsten in gold bars: http://www.youtube.com/watch?v=foELQ7T8_90 But he is using ...
1
vote
1answer
25 views

How to differentiate between ferri-magnetic and para-magnetic substances?

Both are feebly attracted by a magnetic field. I know the difference between these substances(on why these get attracted to magnetic field) but as both get feebly attracted how to find out whether a ...
2
votes
3answers
67 views

Inductance of a solenoid?

My textbook is using Faraday's law to explain the self inductance that happens in a solenoid with changing current. According to Wikipedia, Faraday's Law is: The induced electromotive force in ...
4
votes
2answers
87 views

Intuition behind Faraday's Law?

Faraday's Law seems more like an observation than an explanation. Sure, a changing magnetic current causes emf, but why? How does a changing magnetic field cause electrons to move in the direction of ...