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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time dependent current/ magnetic field

Is there a general way to calculate the magnetic field for a time dependent current of a long thing wire? For ex: If the current is $$ I(t)=I\sin wt, $$ is there a general method to use in order to ...
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1answer
87 views

Stir plate magnetic field RPM relative to stir bar

Observing the use of a variable speed stir plate prompted some discussion about the stir plate motor RPM vs the stir bar RPM and we did not have any physicists handy. The stir plate has a beaker ...
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1answer
42 views

Maximum magnetic strength achievable

What will be the maximum magnetic strength to which a piece of ferromagnetic substance can be magnetised? What will the maximum strength possible for a piece of iron? How would the shape of the ...
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0answers
31 views

Do magnetic fields interact with electromagnetic fields?

I'm not sure if this is even a possible scenario, but what would happen with a permanent magnets magnetic field, when current flows through the magnet? Do the magnetic/electromagnetic force-lines add ...
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0answers
36 views

Electromagnetic fields in daily life [closed]

I have been reading up on electromagnetism lately, and to gain some intuition I wanted to know what effects electric and magnetic fields would have in daily life if they were generated "without any ...
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1answer
81 views

Could we obtain free electrical energy from the Earth's magnetic field? [duplicate]

If there exists a natural magnetic field due to the metallic core of the earth... could we then extract and get free energy from the earth core ??
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1answer
169 views

Magnetic field inside finite solenoid

In my book they don't really derive the equation of the magnetic field inside of a finite solenoid. They just give me equation 1 and image and the end result, equation 2. ...
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1answer
109 views

How to figure out the magnets needed to repulse a given weight?

Given a weight. Is it possible to determine what strength of magnet and what width, length and thickness would be needed in order to repulse that weight a given height? If so, how? To be clear: Two ...
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1answer
66 views

Mysterious magnetic force!

If you have a loop in which current goes clockwise as seen from top, then it forms a north pole if seen from below. Now if a particle with positive charge goes from left to right under it, it ...
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1answer
24 views

Neutral quantum particle in inhomegeneous magnetic field

I'm trying to understand Stern-Gerlach experiment on a computational level. Suppose we have a neutral particle with magnetic moment (e.g. a neutron), and apply an inhomogeneous magnetic field to it ...
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3answers
441 views

Why doesn't Lenz's law predict the behavior of a rod on springs in a magnetic field?

This comes from one of the free response questions from the AP Physics B 2014 exam. 5. (15 points) A conducting rod of mass $m$ and length $L$ hangs at rest from two identical conducting ...
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1answer
71 views

Magnitude and Direction of Magnetic Field Homework Question [closed]

A $150~\text{V}$ battery is connected across two parallel metal plates of area $28.5~\text{cm}^2$ and separation $0.00820~\text{m}$. A beam of alpha particles (charge $+2e$, mass $6.64 \times ...
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98 views

Magnetic field or EM field around wire with electric current?

My question is based on the experiment where iron filings scattered around a piece of paper with a wire carrying an electric current poking through shows magnetic field lines. If you start to vary ...
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1answer
123 views

Effect of Earth's magnetic field on aeroplanes?

As an aeroplane accelerates through the Earth's B-field, it experiences a changing flux $d\phi \over dt$ and a potential difference is induced along its wings. Given the wings are made of metal and ...
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2answers
160 views

Why is magnetic field vector perpendicular to magnetic force vector?

So recently in physics class, we learned about the magnetism right hand rules. One of them states that the index finger points in the direction of the velocity of a particle, the middle finger ...
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1answer
46 views

Heat generated on thin disc plate in magnetic field [closed]

There are the eddy currents in thin circular copper plate thickness h and radius a, in a harmonic magnetic field which is perpendicular to plate and the effect of auto-induction is negligible. Now we ...
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2answers
84 views

How specifically does an MRI machine build an image from received radio waves

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 ...
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0answers
23 views

Calculation of the magnetic field of a solid charged planet-sized sphere

How do I calculate the magnetic field of Mars, which is an almost solid sphere ? I'm a beginner but i'm currently doing a project on Terraforming Of Mars. To create an artificial magnetosphere on the ...
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0answers
15 views

Relationship between the force exerted by a coil and the stress

I can't remember what the equation is for the relationship between the force exerted by a coil and the stress in terms of the current density, the radius and the length. I was thinking just standard ...
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1answer
53 views

Earth's magnetic field

I'm dealing with a problem here. Today my professor asked us a question : How should a metallic wire move in Earth's magnetic field such that she gets maximum potential difference in it's ends: a) ...
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1answer
170 views

In which direction does the current flow in a wire moving north to south along the Earth?

I stumbled upon this question and I can't seem to figure it out. I think you have to use the right hand rule, but it doesn't get me the right answer. The question is something along the lines of: ...
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2answers
101 views

Where does the energy for magnetizing a metal come from?

I saw a young man's science project. He asked this question in a different way "does magnetizing something reduce the magnetic field potential of the original magnet?" His answer experimentally was ...
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2answers
97 views

What can be measured or derived about a remote magnetic field? [closed]

This question related to Why are magnetic lines of force invisible? and is motivated by a comment of @BlackbodyBlacklight, based on that, the illustrating example may depend on that linked question as ...
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3answers
72 views

Is dimensional analysis always sufficient to establish equivalence of quantities?

In dealing with the Biot-Savart law, it was argued that $$ q\frac{d\vec{s}}{dt}\equiv Id\vec{s} $$ using the fact that the units are equal. Does this kind of argument always work? It seems too ...
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2answers
60 views

Magnetic field resistance material: are there any? [duplicate]

I was wondering with a question for a quite long time, thought to ask here. I need to know is there any material or element which can block magnetic field? I mean I am searching for such material or ...
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3answers
152 views

Is an electron attracted to one of the magnetic poles in this scenario?

Do magnets attract electrons? I don't think so, but maybe in certain cases they can be? I guess it would depend on what direction the velocity and magnetic field is in so that the force acting on the ...
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1answer
77 views

Jiles-Atherton model of hysteresis

In my quest for finding a good algorithm to draw hysteresis curve,I have found Jiles-Atherton model which seems to be a rather new model. But I have trouble understanding some of the ...
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1answer
71 views

Electric field and magnetic field question here?

Are the energy of the electric field and the energy of the magnetic field concentrated on their sources OR are they scattered in the environment where the fields arent zero? Can you base your answer ...
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0answers
40 views

Conformal mapping for calculating magnetic reluctance

I work currently on the calculation of magnetic resistance for a air-gap of an electrical machine. For this I am using conformal transformations. I am doing this on a 2D slice. As the machine is ...
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2answers
183 views

Tokamaks and the reason they are not efficient

I'm curious about why tokamaks are inefficient as generators. In laymans terms, what is the main reason(s) tokamaks still cannot be used as generators? My limited understanding of tokamaks tells me ...
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0answers
20 views

Flux, intensity, etc in ferromagnetic core by integral

Cheng, Field and Wave Electromagnetics (newest ed.), ex 6-10, page 252 Some of the examples in this book are kind of sloppily described. Having trouble with this one. We have a toroidal core with ...
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1answer
115 views

Does two Neodymium magnets stick together twice the power?

Assume I use a coil to create B-flux and put ONE Neodymium cylinder magnet (1"diameter & 0.25" thick) close to the flux, it would create 10 lbs force. Does it mean that I put TWO cylinder magnets ...
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0answers
20 views

Electrons Orbiting Sphere Magnet in Crooke's Tube

Were I to assemble a Crooke's Tube and insert a spherical magnet, with the poles of the magnet perpendicular to the electron stream, would the electrons begin to orbit the poles of the magnet as in ...
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0answers
42 views

Determining the path of a particle in a velocity selector

I am wondering how you can determine the path of a particle in a velocity selector provided its velocity doesn't equal $ \frac{E}{B} $. I understand that the equation is derived from this force ...
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26 views

how do you work out the direction of an eddy current

I find it very difficult to work out the direction of the eddy current, can someone please explain the steps in working out the direction of it? there is a following question; I dont understand how ...
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2answers
1k 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 ...
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2answers
220 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. ...
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1answer
83 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 $$ ...
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0answers
22 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 ...
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1answer
77 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 ...
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2answers
69 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 ...
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2answers
149 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?
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1answer
114 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, ...
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1answer
256 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
76 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, ...
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2answers
175 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 ...
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1answer
31 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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10 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 ...
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2answers
62 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 ...
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4answers
82 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 ...