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2answers
122 views

Does a static electric field travel at the speed of light?

Suppose we have a large area where the net electric field is zero. We place a charge q somewhere in this area. How long will it it take for another positive charge q' standing at a distance d from q ...
0
votes
4answers
132 views

Do photons interact or not directly?

All I am asking about is photon (EM wavepacket) photon (EM wavepacket) interaction. I have read this question: If photon-photon interactions are impossible, how are higher harmonics generated? ...
0
votes
2answers
37 views

Changing Refractive Index

Is it possible that the refractive index of a material could change?if so,what are those factors and what kind of variation could they bring?
1
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2answers
87 views

How did Maxwell figure out the speed of light?

The Wiki article is about 2 graduate years of physics beyond my understanding. What is a good high-school rendition of his thought process: regarding his use of the "distributed capacitance and ...
3
votes
1answer
158 views

How to derive $c=1/\sqrt{\varepsilon_0\,\mu_0}$ from integral form of Maxwell equations? [closed]

I've read similar questions and answers given thereto but find them unsatisfactory. So please don't mark my question as "duplicate". The question may as well be a duplicate, but it's still waiting for ...
2
votes
2answers
220 views

How do we get a expression for speed of light $\frac{1}{\sqrt{\mu\epsilon}}$ using Maxwell's equation? [duplicate]

I am a $12^{th}$ class student in India. I am quite new to these interesting concepts. And, I think I've learnt about electrostatics, magnetism, Maxwell's equations very thoroughly. But, my books ...
0
votes
1answer
45 views

“flowing” speed of an electric field?

Consider a capacitor made of two infinite plates which are at a very large distance $d$ from each other. We place a positive charge on a plate and a negative one on the other one. Two electrical ...
1
vote
2answers
57 views

How was the value of vacuum permittivity originally found?

The vacuum permittivity appears originally in Maxwell's equations, used to describe electric fields. The permeability of vacuum was defined using Ampere's force law (itself derived from Biot-Savart ...
0
votes
3answers
223 views

Another objection to Feynman's moving infinite sheet of charge “radiator”

In The Feynman Lectures on Physics Vol II 18-4, A travelling field we are provided the thought experiment of two uniformly and oppositely electrically charged planar sheets of infinite extent lying in ...
0
votes
0answers
54 views

Purported non-constant speed of light

What is going on there to make it appear that light is slower than $c$ ? Here is the popular science news article: Speed of light not so constant after all; Pulse structure can slow photons, even ...
17
votes
5answers
6k views

Do Maxwell's equations predict the speed of light exactly?

I know that $\frac{1}{\sqrt{\mu_0\varepsilon_0}}$ is equal to the speed of light but is this prediction accurate? I mean is it 100 percent accurate?
1
vote
2answers
75 views

Paradox of the magnetic field's collapse [closed]

Imagine two strong electromagnets (X and Y) enough far from each other. Facts: 1.) We know the magnetic fields spreading with the speed of light. 2.) When the magnetic fields reach the other ...
0
votes
1answer
51 views

Has the velocity of propagation of a magnetic field been measured?

I understand the velocity of propagation of a magnetic field is supposed to be c, the velocity of light, but I'm not able to find any experimental tests that this is the case. I believe there have ...
0
votes
3answers
103 views

Will the electron affected by another electron via Coulomb's force affect this electron instantly? [duplicate]

Coulomb's law is strict: $F=k\dfrac{q_1*q_2}{r^2}$ that means that between two charges occurs force. I.e. occurs force on $q_1$ and on $q_2$. If there are two electrons in vacuum with 300 00 000 ...
3
votes
2answers
100 views

Speed of EM waves differ from GWs?

I understand that light travels at speed c in vacuum, when measured locally. This speed has an exact value, not an approximation, because it is defined as 299 792 458 m / s. It is an exact value, ...
4
votes
2answers
351 views

Do electromagnetic fields have inertia? Or, what sets the speed of light?

In all mechanical waves, there is a restoring force and an inertial influence. For example, a plucked string oscillates because the restoring force brings it back to being straight and then the string'...
1
vote
1answer
53 views

In how far can a source term influence the propagation speed of an EM wave?

Unfortunately, I can only find discussions of signal speed for solutions of the homogeneous EM wave equations (e.g. https://arxiv.org/pdf/1111.2402.pdf). Therefore, let me ask here: Can the form of ...
2
votes
1answer
221 views

Virtual photon exchange instantaneously

I have read these questions: Virtual Photon transmission speed of a Static Electric Field? where John Rennie's comments say: Virtual photons can travel faster than light Is there a "...
-2
votes
4answers
165 views

Problem with relativistic mass

We know that relativistic mass of a object is given by: $$m=\frac{m_{0}}{\sqrt{1-\frac{v^2}{c^2}}}.$$ So the mass of an object will become very large if it travels with a speed near to the speed of ...
15
votes
6answers
3k views

Is force due to electric field instantaneous? If not then why?

Suppose a charge $q$ is experiencing a force due to charge $Q$. Suppose we move the charge $Q$ very slowly (no acceleration) what's the instantaneous impact on the charge $q$? How will the $q$ react?
1
vote
1answer
48 views

Shapiro test interstellar/intergalactic

I understand that the Shapiro time delay effect is one of the four classic solar system GR tests. I understand the EM waves have to pop back from a planet beyond the star and then pass next to the ...
6
votes
6answers
504 views

Give an interpretation of what $c=\frac{1}{\sqrt{\varepsilon_0\mu_0}}$ actually means

From my later school days on, the formula that impresses me the most is $$c=\frac{1}{\sqrt{\varepsilon_0\mu_0}}$$ I know how this can be derived, both from Maxwell Equations and more intuitively. I ...
2
votes
3answers
100 views

Electromagnet would emit light?

Light is an Electomagnetic wave. When I create an electromagnet by passing electricity wound around a core and keep changing the electric field, does it emit photons? Is the frequency of ...
2
votes
0answers
179 views

How fast does the electrostatic force travel?

Suppose an electron is created somehow in the universe -- through particle-pair production or what have you. Suppose it is stationary so that electrodynamics (and specifically propagating ...
2
votes
1answer
79 views

Speed of electromagnetic interactions

We know that electromagnetic waves fly with the speed of light, but my question not about waves. Consider a very strong electromagnet that creates a substantial field 3 meters away. Then we send a ...
5
votes
4answers
1k views

Is my argument deducing from Maxwells equations the exclusion of faster than light travel flawed?

When Maxwell's equations are solved, one of the solutions is electromagnetic waves that should move at a certain speed ($c = \frac{1}{\sqrt{\mu_0 \epsilon_0}}$). Now, one could argue that since ...
0
votes
1answer
95 views

Constancy of $c$ from Maxwell's Equations [duplicate]

How do you prove from Maxwell's equations that the speed of light is independent of the motions of the sources that produce the wave?
0
votes
1answer
83 views

Cause of Magnetic Fields

I read this on Quora in this question in an answer by Peter Webb. The magnetic forces are not real forces, they are virtual forces. They essentially derive from the time lag it takes an electric ...
1
vote
1answer
56 views

Oscillating Electromagnetic field

Hypothetically, if I were to move at the speed of light, would I see an oscillating electromagnetic wave or photons oscillating or what?
2
votes
1answer
116 views

Is there any physical significance to the fact that magnetic and electric field are proportional by $c$?

Being that this relation can be derived from Maxwell's equations, is there any physical significance to it outside the fact that the same equations make it the phase velocity of EM waves?
4
votes
3answers
299 views

Does light travel through a waveguide faster than electricity through a wire

So I have heard that using photons to compute is faster than electrons. I was wondering why exactly that is? Is it because light travels through a waveguide faster than electricity through a wire?
4
votes
1answer
73 views

Are these two definitions for propagation speed be the same?

We know for a fact that for any medium with permittivity and permeability $\epsilon$ and $\mu$, the propagation speed of electromagnetic waves is given by $$v = \frac{1}{\sqrt{\mu\epsilon}}$$ We ...
2
votes
2answers
86 views

Evidence for $\epsilon_{0}$ and $\mu_{0}$ being invariant between different inertial frames

Are $\epsilon_{0}$ (permittivity) and $\mu_{0}$ (permeability) invariant between different inertial frames? If yes, what hard evidence does it support that? If no, why would $c$ (velocity of light) ...
13
votes
1answer
2k views

How does $\epsilon \mu = 1/c_m^2$ change when $\mu$ or $\epsilon$ (permeability or permittivity) is a tensor?

I've read that in some materials, $\mu$ can be a tensor, not a mere scalar. (I haven't actually dealt with tensors before, but I'm assuming for my purposes here, it is synonymous with "matrix".) I'...
45
votes
10answers
8k views

Without the Michelson-Morley experiment, is there any other reason to think speed of light is the universal speed limit?

If the Michelson-Morley experiment hadn't been conducted, are there any other reasons to think, from the experimental evidence available at that time, that Einstein could think of the Special Theory ...
7
votes
3answers
785 views

Why is the velocity of light in a medium smaller than its value in vacuum?

The velocity of electromagnetic waves in a medium is smaller than its value in the vacuum: $$v=\frac{1}{\sqrt{\mu\epsilon}}=c/n<c$$ with the refractive index $n=\sqrt{\frac{\mu\epsilon}{\mu_0\...
1
vote
0answers
65 views

Superluminal group velocity in Lossy waveguides

Let's consider a waveguide with $2$ perfect electric boundary conditions filled with a lossy medium modelled with conductivity $\sigma$ and permittivity $\epsilon$ and permeability $\mu$. It is ...
-1
votes
1answer
422 views

Are images formed due to reflection or refraction and what do we see? HOW?

I am getting extremely confused about what we see as individuals : do we see reflected rays or refracted rays and what does our brain interpret? The concept has bewildered me for a long time. Googling ...
8
votes
2answers
275 views

What would happen if a charge could travel at $c$? [duplicate]

We know that an electron can move at sublight speed, but can we figure out what would happen if a charge moved at $c$, surfing the wave of the electric field it has produced? There does not seem to be ...
4
votes
5answers
1k views

Is the speed of light dictated by Vacuum Permittivity, Vice Versa or Neither?

Instinct, and my limited knowledge of Maxwell's Equations and the Wave Equation tell me that the first statement is true. By my interpretation, the relationship between the frequencies and ...
3
votes
1answer
98 views

Can we expect to relate the fundamental constants G and c?

Newton's gravitational constant G tells us about the strength of the static gravitational interaction within our spacetime. The speed of light c can be derived from the properties of spacetime itself, ...
1
vote
1answer
666 views

Does the medium a magnetic field is propagating through affect its speed?

I'm wondering if a material's magnetic susceptibility or magnetic permeability would have an effect on the speed a magnetic field would propagate through it. I know it won't speed it up but I'm ...
16
votes
4answers
3k views

To what extent can speed of light be reduced? [duplicate]

Light slows down upon entering different transparent objects, and the ratio is taken as refractive index of the object. If light can be slowed down, then is there a limit up to which it can be slowed ...
4
votes
2answers
245 views

According to relativity theory, what is the force that two electrons moving radially apart exert on each other?

According to relativity theory, what is the most general expression for the force that two electrons moving radially apart exert on each other? I am looking for a function $$F(r(t)),$$ where $F$ is ...
1
vote
1answer
82 views

What do we mean by speed of light dependent on direction?

I have a statement in textbook saying: When the speed of light is independent of direction, the secondary waves are spherical. When is it dependent on direction and how will the secondary waves ...
0
votes
1answer
77 views

Velocity of propagation of an EM field in vacuum

I am asked to find the speed of propagation $\vec{v}$ of an electromagnetic field, in a region of empty space. The magnetic field is described by $\vec{B} = B_0e^{ax}\sin{(ky-\omega t)} \hat{z}$. I ...
9
votes
4answers
337 views

Why should gluons move at a speed determined by $\mu_0$ and $\varepsilon_0$?

I understand that the speed of light can be derived from Maxwell's equations, giving $c=\frac{1}{\sqrt{\mu_0\varepsilon_0}}$ I furthermore understand how the principle of invariance of laws w.r.t. ...
8
votes
2answers
2k views

Why don't constant motion charges produce waves?

I'm a little confused about the origin of electromagnetic waves. Although I can understand their origin mathematically, I get a little confused about the physical intuition of... Information ...
6
votes
2answers
308 views

Experiment measuring vacuum permittivity and permeability in high speed

Speed of light may be obtained by inspecting the wave equation derived from Maxwell's equations making Lorentz transformation and special relativity necessary to mediate. My questions are: a) ...
0
votes
1answer
431 views

How is light slowing down in a medium thought of in the photon picture? [duplicate]

The speed of light in any medium besides vacuum is smaller than $c$. In a classical way, I just look at that as a wave that propagates less fast, the change in EM-field is passed on slower. How should ...