19

In the image included in your question, one should not view the arrows as literally extending through space or having a spatial length associated to them. The length of these arrows is the magnitude of the field, and they should each be thought of as living inside of their own vector space which is "internal" or "attached" to a given ...


13

While electromagnetic waves do have lateral extension, since the electric and magnetic fields are defined on all of $\mathbb{R}^{3+1}$, most graphical representations, including the one you have included, do not show how an electromagnetic wave extends in all directions. The reason for this is quite simple: representing the entirety of an electromagnetic ...


8

Yes. Often these can be considered plane waves: The vectors represent the electric field of the EM wave. See the description on Commons by Dave3457. Wavefronts can also be spherical, etc.


5

The plane wave depicted in the image is invariant under translations in $x$ and $y$. It fills all of space.


5

I suspect the reason why you're getting seemingly contradictory answers is that you're asking an "is it A or B?" question where the real answer is "no, it's neither of those things." On one hand, no, an electromagnetic wave is not a "pure mathematical line" — it's a fluctuation in the electromagnetic field, which permeates all ...


3

If I interpret your question correctly, you're asking if the E and B fields constitute some sort of spatial displacement (of a medium in which the wave travels, as with water waves or elastic waves in a solid), on the grounds that they are considered to point in a definite spatial direction. The answer is 'no' - they are better considered to be gradients in ...


3

The simple answer is, until now, we haven't found any negative effects on health, and we've looked quite deep. In order to cause any damage from electromagnetic radiation, one of three things has to happen. Either the radiation is high-frequency enough that it can ionize atoms, which leads to ionization damage, or you have to get electrocuted, or cooked. Let ...


3

Any erasing would likely be from thermal effects. If the light heats a spot on the disk above the material's Curie temperature, the magnetic field generated by that spot will relax. That may or may not be hot enough to destroy the disk. You would probably want to use a short pulse from a laser focused on a small spot. This would locally heat the bit in ...


2

What changes between frames in the case of a linear medium is not so much Maxwell's equations as the constitutive relations. The displacement field $\mathbf{D}$ and the auxiliary field $\mathbf{H}$ are defined in the rest frame of the medium as $\mathbf{D} = \epsilon \mathbf{E}$ and $\mathbf{H} = \mu^{-1} \mathbf{B}$, where $\mathbf{E}$ and $\mathbf{B}$ are ...


2

How do you know that the excitations of the Electromagnetic Field are photons The word "field" in quantum field theory does not have the same definition as in classical electromagnetic theory: Moreover, within each category (scalar, vector, tensor), a field can be either a classical field or a quantum field, depending on whether it is ...


2

When quantizing the electromagnetic quadri-potential, one makes the following ansatz : \begin{equation*} A_\mu (x^\sigma)= \int \frac{d^3 p}{(2\pi)^3 2E_p} \sum_{n=1}^2 e^{(n)}_\mu(p)\left(a_{(n)} (k) e^{-i k_\rho x^\rho}+a^\dagger_{(n)}(k)e^{ik_\rho x^\rho} \right) \end{equation*} Where $a^\dagger_{(n)}(k)$ is the creation operator of excitation of the ...


2

You are correct, but the light does have to be really really monochromatic and the polarization has to be strictly defined and exactly fixed. As you point out, if you examine the light through a fixed polarizing filter and if its amplitude changes over some period of time, then there must be more than one frequency present. Polarization can be linear or ...


2

In short: There is a lower limit on the spectral width $\Delta \omega$ of unpolarized light. Therefore, strictly monochromatic unpolarized light can not exist, not even mathematically, while spectrally broad unpolarized and polarized light exists. The following holds for classical light which has a well-defined electric field at each point in spacetime. An ...


1

Almost any high current device will emit 60 hz radiation. There is still some question about its effect on the human body. I have heard it suggested that one should avoid prolonged close contact, such as that had with an electric blanket.


1

TL;DR: Monochromatic light can be unpolarized and polarized light can be non-monochromatic. My answer thus somewhat disagrees with the one by @RogerWood and I will give more details in the following. (This answer has been edited completely upon request, to make it more accessible to a general audience.) Let's look at the two cases. Polarized can easily be ...


1

I think you are seeing the problem wrong, the curl of E its not zero, the text, just say that the $z$ component of $\nabla\times \vec{E}$ is zero that means that there is not magnetic field on the direction of the conductor but there exist magnetif field in other dimesions, for example the $y$ component of $\nabla\times \vec{E}$ is $\frac{\partial E_x}{\...


1

Yes, the observer towards which the lab is accelerating will observe blueshift increasing in time due to Doppler's effect.


1

Think of the light as a stream of photons. Each photon travels in a straight line like you say, but as you shake it the photons given off by the light each get different starting positions. So as you look at the beam of light it may seem to have a wavy shape, but that's just an illusion. Like spraying water from a hose and wiggling the nozzle - the jet will ...


1

Look also at the expression for divergence: \begin{equation} \theta=\frac{\lambda}{\pi w_0 } \end{equation} for 2 beams with the same waist $w_0$, the one with the lower wavelength (higher frequency) will also have a lower divergence. With the equations you posted you can also see that 2 beams with the same waist, the Rayleigh range will be longer for that ...


1

You are right, an omnidirectional radio broadcast would be very faint by the time it reached earth, and very difficult to distinguish from background noise. Projects such as SETI use large amounts of computing power and sophisticated signal analysis algorithms to try to detect a faint signal with a pattern indicating an artificial origin. Instead of ...


1

Electromagnetic waves are still the best bet and distances are huge but we’re reasonably good at sending and detecting weak signals, and constantly improving at that job. We are still communicating with the Voyager probes, even if they have both reached the interstellar region, and signal strengths have energy 20 billions times smaller than needed to run a ...


1

The answer is NO. Gyromagnetic effects limit the rate at which magnetization can be changed. In most situations, magnetization will not respond to frequencies much above a few GHz and certainly not to optical frequencies. However, all-optical switching of magnetization is a recent and active area of research (for example in 'Nature'). All-optical ...


1

I think your colleague may refer to the Heat-assisted magnetic recording(HAMR) driver. Basically, it is using laser as a heater but not a tool to change the electromagnetic field. For details, you may find more on Wikipedia.


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