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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How can I calculate the relative permeability of iron?

I'm a high school physics student, and part of our project requires us to make an electromagnet. We have an iron core, and it will go inside a solenoid. The problem is, we don't know what the relative ...
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1answer
18 views

Magnetic force and terminal velocity of falling loop and falling disc?

According to my textbook, if a square loop with mass $M$ is allowed to free fall (with a magnetic field at the bottom side and as soon as the square loop is dropped then the area inside the loop ...
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1answer
31 views

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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1answer
27 views

Could someone explain the “revolving frame” to me, as it is used in basic NMR?

I am an undergrad intern at a national lab currently working with a basic proton NMR device. The device consists of two big coils which provide the static magnetic field, and a smaller coil, which ...
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1answer
263 views

Why are magnetic field lines perpendicular to the surface of a ferromagnetic material?

It is known that magnetic field lines become nearly perpendicular to the surface of a ferromagnetic material. The quantitative proof which uses the boundary condition requires that magnetization at ...
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1answer
86 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 $n$ ...
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2answers
91 views

In a strong field, how long would it take for domains to align?

How fast is the rate of "switch" for the domains to align with an exterior field? Possibly in milliseconds? I assume it won't take much time since domains are very small, and they only turn from a ...
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2answers
31 views

Time Varying Magnetic Field

What is said time varying magnetic field? I have heard a lot about it and the Internet is not willing to give me any answers. I assume time varying is a qualification, I was reading around here and ...
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1answer
37 views

Current in Magnetic fields

I have two magnetic fields question (high school level) which require clear answers... When a current carrying conductor, such as a copper wire, is placed in a magnetic field it will experience a ...
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1answer
72 views

What is equation to find force of magnetic attraction

I was wondering as a student, when I was playing with magnets I thought like Gravitational force equation of Newton's Gravitation Theory, can we also calculate force of an magnetic attraction on an ...
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1answer
34 views

Is the field generated by an electromagnet always proportional to its current?

Imagine that I use a long wire to create an electromagnet. Let's also assume that the current flowing along the wire is constant, and that the wire is winded on the vacuumm. Is the magnetic field ...
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1answer
59 views

How do you levitate a foam rock? ('Endless Second' artwork)

I saw this in an art museum: How is this possible? The materials used to make this were foam, wood, stone dust, paint, electromagnets, and metal. I would like to know how this was make and how I ...
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3answers
191 views

Conservation of energy in electromagnetism?

How is energy conserved in electromagnetism? Is it hinted only from Lenz's law or from Maxwell? Also, if a solenoid's flow of current produces a magnetic field, and from the magnetic field forces are ...
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0answers
13 views

Torque per unit length on infinite rotating charged cylinder

For homework I have the following question, but I am stuck on finding the torque on the cylinder. An infinite cylinder of radius $R$ carries a uniform surface charge $\sigma$. We start rotating the ...
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0answers
12 views

Temperature stability of permanent magnets

Hello physicists/engineers, I have a somehow very specific question I hope some expert can answer me: I'm working at university and try to build an experiment which requires comparable high magnetic ...
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2answers
270 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 ...
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0answers
59 views

How do I use the direction of a cross product?

The question is: An electron is projected at a speed of $3.70×10^6\text{ m/s}$ in the $u=\frac{(i+j+k)}{\sqrt3}$ direction into a uniform magnetic field $\vec {B} = 6.43 i + 3.43 j −8.29 k$. ...
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1answer
62 views

Work done by magnetic field on magnetic dipole

In the above slide, it reads that $W=\int\mu B sin(\theta)d\theta=\mu B cos(\theta)$. But, I thought that $\int\mu B sin(\theta)d\theta=-\mu B cos(\theta)$ by some calculus calculation. Can ...
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1answer
247 views

Is it possible to kill a human with a powerful magnet?

I'm asking in terms of physics. Can powerful magnetic induction rearrange spins of my body in such way I will die? How? Or maybe it can rip all iron from me, which would make my blood cells useless? ...
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0answers
19 views

30kHz solenoid and power amplifier design

I have some difficulties designing my experimental apparatus: The goal is creating a Solenoid in air (or iron powdered core) able to produce at least 50G of peak B field on his axis at a distance of ...
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2answers
284 views

Is magnetic force non-conservative? [duplicate]

If magnetic field is conservative, then why not the magnetic force? My professor thinks it is non conservative but he couldn't explain to me why?
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1answer
40 views

How is magnetism ''conducted'' through a non-magnetic metal?

I have a ball of metal about an inch in diameter and a concave disc of another metal (which is magnetic) around the ring of the disc (about $12 {\rm mm}$ in diameter). I don't know which metals they ...
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0answers
10 views

Does Hall Effect increases the resistance of a wire?

If a current in a wire is flowing perpendicular to a magnetic field, the Hall effect will be observed, which is caused by the forces from magnetic fields 'pushing' the electrons to one side or the ...
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1answer
109 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 ...
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8answers
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Can the magnetic lines of force of two or more magnets intersect each other?

Basic property of magnetic lines of force is that, they can never intersect each other. Among the two points given below, which one is correct? Magnetic lines of force of same magnet can't intersect ...
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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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2answers
44 views

What is the direction of area vector while calculating magnetic flux?

In my textbook, as a preliminary to Faraday's law of induction, magnetic flux is defined over a closed loop as $$\Phi_B = \oint \vec{B}\cdot d\vec{A}$$ Then it draws a parallel with electric flux ...
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0answers
22 views

Sphere in homogenou magnetic field

I have to find out the magnetic dipole moment of sphere in homogenou magnetic field in the limit $\mu_r\rightarrow+\infty$. I don't know what does the condition $\mu_r\rightarrow+\infty$ mean. Does ...
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2answers
174 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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2answers
156 views

Flux cutting and flux linking?

I am a bit confused about the difference between flux cutting and flux linking when talking about magnetic fields and induced EMF. I was originally under the impression that flux cutting was when ...
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1answer
44 views

Equal and opposite electron flows in a magent?

If the electron flow in a magnet is say from South pole to North pole, then I can understand why you can't put the two north ends of magnets together, as the two flows of electrons repel each other. ...
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2answers
306 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 ...
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2answers
67 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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1answer
155 views

Magnetic field when moving into the influence of a ferrous object

Suppose I have a magnetometer. I am on the Earth's surface, away from the influence of other magnetic sources. Assuming the magnetometer is aligned with the reference frame, it should read only the ...
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0answers
11 views

Zero field cooled / field cooled susceptibilities

I'm studying magnetic properties of nanoparticles in a liquid carrier and trying to understand better zero-field-cooled/field-cooled curves. We use the Stoner–Wohlfarth model and Chantrell ...
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3answers
87 views

How long does it take a magnetic field to join both ends?

My question is: when a electromagnet is activated, the field must take time to form at both ends and stabilize. What is this time? Or, to put it differently, what is the speed at which the magnetic ...
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2answers
376 views

Electrostatics/ magnetostatics: why is $\int_\text{all space} d\vec r \; \nabla \cdot(\vec A \times \vec B)$ equal to 0?

I'm reading electrodynamics notes and come across that: $$\int_\text{all space} d\vec r \; \nabla \cdot(\vec A \times \vec B)=0$$ in case of magnetostatics and: $$\int_\text{all space} d\vec r \; ...
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0answers
16 views

How is demagnetizing field described when using Ampére's loop current?

A magnetic moment is sometimes described using circular current loop instead of dipoles. In that case, how do you define the demagnetizing field? Say you have a circular current loop centered on ...
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0answers
25 views

Quantum Locking Superconductors on Earth's Magnetic Field

Is the earth's magnetic field strong enough to hold a quantum locked superconductor, or the superconductor wouldn't be able hold its own weight? How strong should be the earth's magnetic field to ...
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0answers
117 views

How can a magnet have a greater magnetic field strength than a bigger, heavier and more powerful magnet made of the exact same material?

Here are some informations I found on the magnetic field strength (also called "magnetic flux density" or "magnetic induction", commonly denoted as B and expressed in tesla or in gauss) of an average ...
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2answers
71 views

How do we convert between the maximum value of the adhesive force (in kilograms or in Newton) of a magnet and its magnetic field strength (in tesla)?

On the following website they indicate how powerful is a magnet by giving the theoretical maximum value of its adhesive force in kilograms or in Newton (its adhesive force at a distance of zero). ...
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0answers
43 views

Freely Falling Bar in a Magnetic Field

I have a horizontal bar on vertical rails and we can consider that does not exist any friction. Perpendicular to the plane of the rails it exists a magnetic field $B$. I am asked to find the ...
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4answers
79 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 ...
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2answers
53 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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1answer
77 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
94 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 ...
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1answer
46 views

What happens to atoms in extremely strong electromagnetic fields?

I know that strong gravitational fields on the order of neutron stars (at the crust) atoms get compressed so tightly, the empty space between them is significantly reduced and it becomes denser. ...
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2answers
561 views

Which mathematical operation does the right hand rule for current come from?

I am currently wondering about this famous rule: Where does it come from mathematically that when you point with your thumb in the direction of the current, your curved fingers will point in the ...
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1answer
58 views
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1answer
266 views

Moving in a heart!

You can find the symbol of love, the heart, by looking at the motion of a charged particle that's emitted from a hot wire in a specific electromagnetic field. The electric field is directed radially ...