# Tagged Questions

The classical theory of electric and magnetic fields, both in the static and dynamic case. Also covers general questions about magnets, electric attraction/repulsion etc. Distinct from electrical-engineering.

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### Electric & Magnetic fields - clarification

If (changing electric field)=(magnetic field) and (changing magnet field)=(electric field), then why is there a constant magnetic field around a current carrying wire when the electric field does not ...
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### Does the weight of an magnet raise when balancing an object?

I was wondering if say I use an magnet which is facing positive and then I expel an another magnet above it which is facing the positive with its positive side and I ensure the magnet does not rotate ...
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### 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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### Dielectric boundary

I am trying to determine why electric field may be confined to a certain region if there is a large difference in the permitivity for example if electric field flows through water and then reaches a ...
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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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### Online course on theoretical electrodynamics [duplicate]

I'm looking for good online course for an introduction into theoretical electrodynamics. However, it seems that the MIT opencourseware only contains partial lectures for this topic. Has anyone got a ...
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### Creating a atmosphere bubble in space with electromagnetism

would it be possible to contain an atmospheric bubble in space with a magnetic field, and wouldn't doing so protect it from solar radiation also?
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### light penetration in the ocean

Is there an equation that describes the percentage of solar energy per wavelength that penetrates the ocean surface? For example, this website states that only 44.5% of the surface light reaches a ...
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### 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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### How a plasma reacts with an AC electromagnet

Any metal conductor such as aluminium or copper is a conductor because of the free electrons in such metals. Plasma also has free electrons so I would like to know if you can repel plasma the same ...
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### Can a classical (or quantum) field, particularly the EMF, have a frame of reference?

I understand that a massless particle (such as a photon) cannot have a frame of reference. But the electromagnetic field does have mass; does it have a frame of reference? If so, I have a second ...
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### 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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### Any easily available ferromagentic material with $T_c$ in room temperature?

I want to experiment it in my house or office. I think it would be of great fun to see the transition in real life.
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### Visualization of electromagnetic field [duplicate]

In the Wikipedia article about electromagnetic radiation one can find the following picture: But shouldn't the E and B field be 90$^\circ$ out of phase? In the depicted way the energy isn't ...
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### 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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### Why does magnet attract iron but not other metals?

While searching, i found this page: http://timesofindia.indiatimes.com/home/stoi/Why-does-a-magnet-attract-iron/articleshow/4298171.cms but it does not have full explanation. So Please tell full ...
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### Magnetic field in materials with non-constant magnetic susceptibility

I'm quite lost what $B$ and $H$ is. It seams to me that most of the texts I read do quite poor job in explaining them properly. They are explained only in cases when magnetic susceptibility is ...
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### How much power would it take to stop a bullet with a magnet?

If a 7.5 gram copper-jacketed lead bullet (say, a 9x19mm Parabellum) was travelling at 360 m/s, how much power would it take to diamagnetically stop it in the space of one meter? This question comes ...
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### How does information about charges propagate through the electromagnetic field

I understand how the wave equation works, and therefore how light moves through the EMF; this question is not about that mechanism. But when a charge moves in space, information about its location ...
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### How do the electric or magnetic fields contain momentum?

I have recently come to know that the electric and magnetic field contain both linear and angular momenta, which are known functions of the electric and magnetic fields at any given point in space and ...
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### Force between two current carrying parallel wires, multiple proof? [closed]

Having two current carrying (currents $I'$ and $I$) wires of length $a$ parallel to the $z$-axis, one with end points $(0,0,0)$ and $(0,0,a)$ and one from $(a,0,0)$ to $(a,0,a)$, I'm looking for the ...
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### Field interaction betweeen two point charges?

[SOLVED] Consider two particles A and B having equal charges and placed at some distance. The particle A is slightly displaced towards B.So, Does the EM force on B increase(+/-) as soon as the ...