# 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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### Do physical entities with one dimension equal to 0 exist?

Within mathematics, a lot of entities with one or more size equal to zero exist and are fluently manipulated. For example, within $\mathbb R^4$, the entity defined as $z=0, t=2$ is a plan, the one ...
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### Why does magnetic field and not electric field invert in a reflection? (related to another question)

When you are talking about an elctromagnetic wave that reflects on a surface (for example here), why do you say that the reflected magnetic field inverts and not the electric field? \begin{align} E_+ ...
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### Relationship between the g-factor and the gyromagnetic ratio?

From what I have read the g-factor and the gyromagnetic ratio are two different quantities. It appears to me that the gyromagnetic ratio is the ratio between (any) angular momentum and the magnetic ...
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### Electric field produced by polarized medium at the surface of a conductor

Suppose we have some conducting sphere of radius $R$ and charge $Q$ submerged half way into a medium with permittivity $\epsilon_1$. I have deduced that the electric field produced by the sphere will ...
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### Why can't electrons leave negatively charged objects in a vaccum?

If an object is negatively charged, and electrons repel each other since they have like charges, why doesn't that negatively charged object "kick away" electrons? Why doesn't diffusion occur? Why ...
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### How does electrical energy gets converted to sound energy?

I have seen that inside headphones there is a magnet with a coil of thin wire around it. There must be longitudinal waves coming out of it that is why we can listen to audio. There must be pressure ...
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### Motion of Particle due to Lorentz Force

So my professor gave us the following question: A particle with electric charge $Q$ and mass $M$ is initially traveling with velocity $v_0$ in the $x$ direction at time $t= 0$. There is a constant ...
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### How to attract liquid metal with magnets

I would like to know if there is any way that I could make mercury or another liquid metal be attracted or repelled by magnets. Absolutely any solution would be okay with me. For example... can I ...
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### Data analysis for a magnetic hysteresis loop

I'm a physics undergrad and I have MOKE data for a magnetic material (thin permalloy film on a silicon substrate). Here is one of the hysteresis loops I obtained, plotted using python: The form of ...
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### What causes the magnetic field around a wire with current to be circular and perpendicular to the flow of current?

I understand that a moving charge will produce a magnetic field, but what causes them to appear circular and perpendicular to the flow of current, as they are?
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### magnetic friction

If you take attracting magnetic fields, or opposing fields, and rotate them in opposite directions in close proximity, would this not generate an increase in temperature? This would also conclude that ...
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### Resistance in A.C. circuits

Why do electromagnets offer maximum resistance in A.C. circuits?
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### EMF produced by mutual induction

In the phenomenon of mutual induction, when primary coil is connected to an A.C. suppy, does the induced EMF in secondary coil also keeps changing with the changing magnetic flux?
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### Induced Current in a wire

I am just surprised why EMF and Current are not induced in an unclosed wire. I know Maxwell's equation is only defines closed integral. But it doesn't means that it is not generated in a unclosed wire....
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### induced Current I

I am working with the Problem which I've seen in a book. That Problem was : Direction of induced current I can't find any meaningful explanation for this problem in any source. So, I am working with ...
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### How can one meaningfully say that one field generates the other in an EM-wave?

This is a follow up question to: Do the electric and magnetic components of an electromagnetic wave really generate each other? Clearly there are nuances of how one states the "mutual induction" ...
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### Why is Kirchoff's Current Rule valid?

The fact that Kirchoff's Current Rule is valid means that whatever current flows in flows out. But this will only be valid for a steady current circuit, that is, when there is no accumulation of ...
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### Advanced classical electrodynamics book [duplicate]

As I have already studied Griffiths, I want something with modern and advanced approach both towards theory and problem solving.
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### relation between amplitude and frequency of a rotating electric field [closed]

I generated a rotating electric field produced by Ex=cos(wt) Ey=cos(wt-pi/2) in x and y directions. I ran a simulation and seems only in certain amplitudes and frequencies it makes a rotating field. ...
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### Magnetic Field Flux Density Disambiguation

The Electric Field is defined as the electric force exerted on a positive test particle: $$\vec{E}=\frac{\vec{F}}{q}$$ The Electric Flux is defined as: $$\Phi=\iint \vec{E}\cdot \vec{dS}$$ The ...
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### Electrical work and Coulomb's law

In some text books I've encountered the calculation of electrical work done on a point charge moving in an electric field (e.g. when demonstrating that electric force is conservative) is done by ...
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### Energy stored in magnetic field [closed]

I have encountered the problem: Find the magnetic energy stored inside a 1m length of wire carrying 10 amp. The wire is 1 mm in radius, and the current density is uniform. I have found a solution ...
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### Where does wave frequency come from

I am trying to wrap my head around where do oscillations in electromagnetic waves come from. As an example if I would take a string of guitar and ring it, it would produce a certain sound based on the ...
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### Why must this boundary condition be met? (Electromagnetic wave at interface between two mediums)

My textbook says that The laws of Electromagnetic Theory (Section 3.1) lead to certain requirements that must be met by the fields, and they are referred to as the boundary conditions. ...
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### Difficult induced current problem [closed]

consider the following setup shown below in the diagram. A circular conducting ring is placed in a increasing magnetic field into the page.Points $A$ and $B$ contain two bulbs. Initially both are ...
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### How Special Relativity causes magnetism

So my physics teacher assigned us an article about how special relativity causes magnetism in a wire with a current, even with the low drift velocities of electrons in a current. It seemed that the ...
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### How can one confirm creation of magnetic graphene?

Recently my high school physics teacher contacted me looking for an expert to ask about this situation. I am paraphrasing his correspondence below: I just had a a student accidentally create ...
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### What is the limit of the finite solenoid equation?

I'm trying to work out how long to make solenoid in order that the field is uniform over a certain length. I was wondering if there was a formula for this or any rule of thumb? I know the field inside ...