Questions tagged [electromagnetism]

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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Electrostatic Energy of a solid sphere with cavity

Determine the electrostatic energy U stored in the sphere I tried to use $U = ε_0/2 \int E^2d\tau$ for all space. So I find that $E = \frac{(R^3 - b^3)\rho}{3ε_0r^2}, (r>R)$ where $\rho$ is the ...
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Geodynamo theory convection column

I know the Taylor-Proudman theory and there are convection cells in the core. And the geostrophic motion becomes helical flow (z-dependent) in the spherical geometry. However, why this helical flow ...
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How can I prove poisons equation from direct substitution

I’ve got this question where I should take the laplacian of electric potentials main formula, then it should hold the poisson’s equation. I’ve somehow gotten close to doing this but I just can’t get ...
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On Magnetic field due to a long straight wire experiment [on hold]

My question is what error can happen in the experiment if distance is ->0?
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Electrostatic energy of any charge distribution sum up to charge Q should be equal over the whole space?

Intuitively I think that even if you have two different charge distribution but their charges are sum up to the same charge Q, their electrostatic energies over the whole space should be same (Maybe ...
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A doubt and different approach regarding “A hypothetical magnetic field existing…”

A popular question from the book HC Verma's Concepts of Physics goes like this:- "A hypothetical magnetic field existing in a region is given by $$\vec{B}=B_{0} \vec{e}_{r}$$ where er denotes the ...
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Magnetism question from REE (Roorkee Entrance Examination) 1991 [on hold]

A short magnet of magnetic moment 6 A.m2 is lying in a horizontal plane with its North Pole pointing 60 degrees east of north.Find the net horizontal magnetic field at a point on the axis of the ...
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What are some good model quantum systems in external electric fields?

I want to understand a few things on the behavior of atoms and molecules in (weak, non-ionizing) external electric fields. For this, I am looking for model systems that might have an easily ...
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Cross product in Physics [on hold]

The most famous cross product in physics is the one linked to Lorenz's force. In which other models that describe physical interactions is the cross product used? Are there other laws related to the ...
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Misunderstanding the calculation of the potential for a system of 2 concentric shells

Let's say we have 2 concentric shells. The little one has a charge $Q_1$ and a radius $R_1$ and the greater one has a charge $Q_2$ and a radius $R_2$ with $R_2$ > $R_1$. We want to calculate the ...
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Can we create artificial one-way electromagnetic attraction by just using photons?

As usual, I apologize for asking dumb questions, and I hope this isn't one of them. If we know that photons are the carriers of the electromagnetic force, could we somehow create a device that simply ...
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Is pair production a type of elastic scattering?

Pair production is the creation of a subatomic particle and its antiparticle from a boson. Pair production often refers specifically to a photon creating an electron–positron pair near a ...
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Why do tokamaks have so few toroidal field magnets?

From the ITER webpage itself, the tokamak has only eighteen toroidal field magnets. If the magnetic field is directly and linearly dependant on the number of coils around the torus, then why did the ...
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EM parameters of fiberglass

My question is very short: does anyone know the electromagnetic parameters $\epsilon$, $\mu$ and $\sigma$ of the 'fiberglass' material, in X-band? I searched on various sources but I didn't find any ...
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Leaked electric field in Transmission Line theory

In the previous image I can't understand why the leaked electric field in plate conductors is axial (On the same axis of propagation), And if it becomes axial then the wave in the conductor is not <...
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Current densities in a 3D object

What is a smart way to calculate current densities in 3D objects with unorthodox boundary conditions? For example, J(x,y,z) in a cube with constant resistivity with applied voltages Va in a vertex ...
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Lorenz Gauge Condition in Helmholtz equation

I am working with electromagnetic fields in the frequency domain. I do not understand why we can apply the Lorenz condition in Helmholtz equation. What is its physical meaning? Any help is appreciated....
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Standing Wave in a transmission line and Resonance

let's consider a transmission line of length L closed on a mismatched load. So, there will be a travelling wave and a reverse travelling wave: V(z) = V+(z) + V-(z) My question is: will there always ...
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Why should $E$ and $B$ both contribute $(1/2) kT$ in equilibrium radiation?

At high temperatures/low frequency, energy distributes itself by equipartition. There's a factor of $\frac{1}{2}kT$ for each degree of freedom that contributes quadratically to the energy. So, for ...
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Qualitative definition for potentials

I am doing an E&M course and just started with the concept of electric potential, potential difference, etc. I know how to work with them mathematically, but I don't have an intuition for their ...
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Vector components for the dipole of water

I was looking online for the components for the dipole moment vector of water in the molecular frame. Does anyone know what the values would be for $\mu_x$, $\mu_y$ and $\mu_z$ for a water molecule in ...
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Drone's sufficient engine RPMs initiated by Magnetic Fields

I've seen many videos where magnets are used to initiate and boost RPMs. Most of them are fake, where people are using compressed air at the backstage. Did anyone of you actually tried to challenge ...
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In a simple resistor circuit, does the current reach V/R instantaneously?

Essentially, if I were to plot current against time for a simple circuit with a DC cell and a resistor in it, would there be a non-flat profile from time $t = 0$. So, between $t = 0$ and $t = t_1$, ...
I know that $I=\int_AJ(\vec{r},t)d\vec{A}$ now can I say that $I(\vec{r},t)$?
I know that $I=\int_AJ(\vec{r},t)d\vec{A}$ and if $J(\vec{r},t)=\sigma(\vec{r},T) \vec{E}(\vec{r},t)$ we have $I=\int_AJ(\vec{r},t)d\vec{A}=\int_A\sigma(\vec{r},T) \vec{E}(\vec{r},t)d\vec{A}$ now can ...