# Tag Info

### What happens to the charges in an inductor when you induce a voltage?

If you connect to an ac source you have an ac current in the second wire , same as in a larger transformer ,if you connect to a dc source you have no effect on the second wire except in the first ...
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### Is First-Class Constraint Generator of matter Gauge Symmetry in EM example?

The solution to OP's problem is to include a pertinent matter sector in the E&M Lagrangian (3) (in OP's case: a complex scalar $\phi$). This produces the source term in the first-class secondary ...
• 206k
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Accepted

### Can plasmas have eddy currents?

Yes. Induced currents in plasmas can be useful. The poloidal field in a tokamak is an eddy current induced by a magnetic field that threads the torus.
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### Why the frequency component is not included when the energy of a wave is described?

According to particle theory, the energy of a photon depends on frequency which makes sense. But in classical theory, how is it included? I am not seeing it. Energy density vs. energy flux One has to ...
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### Is First-Class Constraint Generator of matter Gauge Symmetry in EM example?

From @Andrew's comment, I know how to solve it. In scalar QED, EM field would couple to current $J^{\mu}(x) = \phi^{\star}(x)\partial^{\mu}\phi(x) - \phi(x)\partial^{\mu}\phi^{\star}(x)$, and the ...
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### Why the frequency component is not included when the energy of a wave is described?

This really depends on the wave. If it's a wave in rope, there is kinetic energy associated with the velocity of the rope moving up and down, and in the linear limit: $$v \propto A\omega$$ which has ...
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Accepted

### From what equations is magnetic field uniquely determined for a given current distribution?

The domain is important. The solution is given by Biot-Savart if it is the entire $\mathbb R^3$ space, with some assumptions on the regularity and decay of $B$ (e.g. $L^2$). In this case, you can ...
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### How to avoid the ordinary Coulomb solution in QCD?

First, I think your proposed current would break gauge invariance, but that's a relatively trivial problem in that I think you could reformulate your question getting around that issue. The bigger ...
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### Diffraction when the wavefront is not parallel to the plane

This is how you derive Snell's law: https://ocw.mit.edu/courses/3-024-electronic-optical-and-magnetic-properties-of-materials-spring-2013/480e12b984eb21a5e88b8ee5cc051ef8_MIT3_024S13_2012lec22.pdf ...

### What effect do two perpendicular magnetic fields have?

Maxwell's equations are linear, that means: The magnetic field of two loops of currents is then sum of the magnetic fields of each loops of current.
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### How is a steady current maintained in case of motional EMF if net force on electrons is zero?

if they are slowed down or are sent in random directions once they encounter resistance in the wire then how should a steady current keep flowing? If the rod is isolated, only then electric charge ...
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### Gauge theory of Electomagnetic Potentials - 2nd order derivatives

The Gauge fixing condition must be (1) accessible (This is addressed in Gabriel's answer), and (2) it must uniquely fix the gauge. In E&M one way to see that you get the gauge degree of freedom is ...
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### How is a steady current maintained in case of motional EMF if net force on electrons is zero?

Indeed there is no current in the rod once the force on the electrons become zero. While the rod was entering in the magnetic field , the magnetic force acted on the free electrons to produce a ...
1 vote

### Gauge theory of Electomagnetic Potentials - 2nd order derivatives

This is only a partial answer to your question. What you say about X and Y being linear is not necessarily true, as I have seen other guage choices like the Weul gauge, $A_t=0$, used in QFT, or the ...

### Understanding Symmetries and Invariances in Electrostatic Fields

The concept of symmetry plays an important role in all branches of Physics, and electrostatics is a good playground for developing an intuition on how symmetries works. A little disclaimer: I do not ...

### What is the relation between the Faraday effect and the Zeeman effect?

Most magneto-optic effects, such as the Faraday or Kerr effect, are classical phenomena. You don't need to explain things in terms of photons or atoms to understand these effects. The Zeeman effect ...

### Would a gauss rifle based on generated magnetic fields have any kickback?

There is one questionable assumption that the pro-recoil camp is making. A normal firearm PUSHES the projectile down the barrel. The force applied is from a single direction horizontal to the user. A ...

### Directionality of EM Waves in Double Slit Experiment

The diagram on the left is in the xy-plane and you can liken it to a contour map taken at an instant of time, like a photograph. Initially let me assume that the incoming light is plane polarised in y-...
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### Analog between Electromagnetism and Gravity

In electromagnetism, if you have a $$\mathcal{L} = -\frac{1}{4} F^2 + A_\mu J^\mu$$ where $F^2=F_{\mu\nu}F^{\mu\nu}$ is the Maxwell term ($F_{\mu\nu}=\partial_\mu A_\nu-\partial_\nu A_\mu$), the ...
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### Friction and electromagnetic force

I disagree with Bob D that there is no underlying relationship. Instead, what I'd say is that friction is applied electromagnetic forces. Electromagnetic forces dominate interactions between atoms. ...
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### Is magneto-optic Kerr effect discernible for material with natural optical activity?

From an experimentalist's point of view: If the material's chiral structure is independent of the external field or magnetism, then the sample's optical activity will be calibrated out of the result ...
1 vote

### Difference Between Plasma Potential and Floating Potential in a Plasma

The floating potential is the potential a metallic body acquires in the plasma when it is not connected to any electrode, so that the charged fluxes arriving to it have no where to go but to change ...
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### Can photons interact with one another?

Most of the time they interact by changing a medium which changes the properties that the photon sees. But another possibility is HOM interference, in which the possible outcomes of the different ...
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### Can photons interact with one another?

Photons can interact with each other. However, the interaction is very weak in the vacuum. I'm not sure this can be explained using a simple explanation from wave-particle duality. The full ...
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### Quick question regarding Larmor precession and bar magnets

https://en.m.wikipedia.org/wiki/Ferromagnetic_resonance: ‘ Ferromagnetic resonance, or FMR, is coupling between an electromagnetic wave and the magnetization of a medium through which it passes. This ...
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### Why is the length of a Faraday cage's lattice relevant to what wavelengths it blocks?

Think of each hole in the Faraday cage as a very short waveguide. If the wavelength of the radiation is short enough (roughly $\lambda < 2d$ where $d$ is the diameter of the hole), then that ...
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### In a simple battery + resistor circuit, what form of energy is lost from the electrons upon exiting the resistor?

I was writing an answer to a very similar question that was closed and merged in this one, so excuse me if I repeat the other answers. The particularity of this other answer is that it called for an ...
1 vote
Accepted

### Flux change through a loop

This comes from Faraday's law. I believe it is only valid in quasistatic (no radiation generated) situations. Faraday's law in differential form is $$-\frac{d\Phi_B}{dt} = \varepsilon.$$ If you have a ...
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Accepted

• 97.9k

### Comparing Electric Potential Energy of two Charges

You can calculate the energy of the charges explicitly. For simplicity, let us reduce the problem to a one-dimensional case. Take fixed charges $-Q$ at $z=-a/2$ and $+Q$ at $z=a/2$. These act as the ...
1 vote

### Comparing Electric Potential Energy of two Charges

In the case that A and B both have the same positive charge: remember that potential energy associated with a position (it is not defined as something that requires two positions e.g. A and A') is the ...
Accepted

### What is the impressed current density?

$\mathbf{J}_e$ is the "impressed current density" in the source/external battery, etc. (Ohm's law need not hold in the source, so in the general discussion, there is a reason not to express ...
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### Why the $T_1$ recovery & $T_2$ decay are independent?

When you say the videos "show them dependant on each other", perhaps your confusion arises because they both evolve with time. I think a simple classical explanation is best, so I won't go ...
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### How do you convert from Townsend Unit $\rm Td$ to $\rm kV/(cm bar)$?

An educated guess by an insider. Everything rob says is correct and everything calculated in the question is correct. I have been making calculations with E/N values and I also have to convert from V/...
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### Most generic form of refractive index tensors

Symmetry: In non-magnetic media, the real part of the refractive index tensor is typically symmetric due to energy conservation principles. This symmetry is related to the reciprocity theorem in ...
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### Why the $T_1$ recovery & $T_2$ decay are independent?

The first thing you have to note is that: no, the transverse $M_{xy}$ component does not exchange energy with the longitudinal $M_z$ component for the magnetization $\vec{M}$ to return to equilibrium. ...
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