# Tagged Questions

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### Reflectivity and transmissivity greater than 1

In plasmonics, it is often seen that reflection coefficient and transmission coefficient are greater than 1. How is energy conservation valid in such cases?
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### Any good electricity and magnetism books for highschool students? [duplicate]

I really want to learn about electricity and magnetism for a long time but never have gotten to it, are there are good books that are conceptual on the topic of electromagnetism? I do not know ...
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### Why is the electric field perpendicular to a circuit zero?

Griffith briefly addresses the uniformity of the electric field in a wire using Laplace's equation by assuming that the electric field is always parallel to the wire (i.e. $\mathbf{E}\cdot\hat{n}=0$). ...
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### What is Coulumb force at zero separation in classical picture [on hold]

Assume a classical world. What would be force between 2 point charges if their separation tends to zero? Assume charges are static. My professor claimed it would be finite. I request you to ...
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### How many photons are needed to make a light wave?

What is the smallest number of photons needed to make a "light wave"? In other words, how many (coherent?) photons start to exhibit classical behavior? For example, how many photons are needed to get ...
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### Flow from higher potential region to lower potential region

In Thermodynamics, it is said that heat transfer takes place from higher temperature to lower temperature. Things having higher temperature have higher potential energy because of more vibratory ...
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### What is the area in Faraday's law if we have only a piece of metal moving in a magnetic field?

If a piece of metal of length $l$ is moving with a speed $v$ in a region where there is a uniform magnetic field $B$ perpendicular to it, there will be a potential difference across its terminals ...
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### Fine Structure and Fine Structure Constant - intuitive relation?

How does the fine structure and fine structure constant relate to each other, intuitively? I've seen $\alpha$ extrapolated as a term in energy calculations for fine structure, but is there a ...
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### Confusion in the derivation of the potential of a magnetic shell

I am reading an old book on electromagnetism (THE MATHEMATICAL THEORY OF ELECTRICITY AND MAGNETISM) and I have some confusion in the following pages: First let me clarify what a "magnetic shell" ...
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### What is relationship between electromagnetic mass and rest mass?

Is there a direct equation which compares rest mass $m_°$ and electromagnetic mass $m_{em}$? Nothing on web I found. $m_{em} = \frac{4 E_{em}}{3c^2}$ 4/3 problem The final solution of the ...
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### Lorentz force in different reference frames?

I have been introducing myself to special relativity and relativistic electrodynamics, and became curious about the similarity of the electric and magnetic forces. I'm trying to show that the combined ...
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### Will accelerated observer see radiation from the charge that is at rest in observers's frame?

So I had a huge debate about this with my friends. Imagine that you are in a non-inertial frame of reference. For simplicity, assume that frame is accelerated along x-axis. You have held a charge in ...
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### What is the physical meaning of a magnetic conduction current?

In electrodynamics, it is possible to have an electric conduction current, whereby $J=\sigma_e E$, with $J$ being the current, $\sigma_e$ the electrical conductivity and $E$ the electric field (this ...
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### Calculating charge density $\rho(r)$ using Gauss law (both forms)

Below is a question given in my assignment. I tried applying Gauss law in both forms, differential and surface integral form. But both there is a difference by a factor of $2$. Is the differential ...
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### How does always the magnetic field lag the elctric field in a conductor?

In conductor, the relation between the phase of the magnetic field $\delta_B$ and that of the electric field $\delta_E$ is given by $$\delta_B-\delta_E=\tan^{-1}(\frac{\beta}{\alpha})$$ where $\alpha$ ...
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As in the title, I'm wondering is it possible. I think it is possible, because we have powerful enough radiotechniques and gamma radiation are just EM waves, not particles. However I think is useless,...
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### De-merits of the application of Laplace's Equation to find electrostatics potentials

QUESTION: What are the de-merits of the application of Laplace's Equation to find electrostatics potentials? Our professor told us that the answer was as follows: It can be used only when the ...
In Griffith's book on Electrodynamics, while discussing the propagation of electromagnetic wave in a conducting medium, he set $\rho_{free}=0$. He argues that, any extra charge given to the conductor ...