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43

Refraction of light in water droplets, leading to the formation of rainbows, is not limited to the visible range. Experimental evidence, compelling due to its simplicity, is shown in the following images taken by University of College London Earth Sciences professor Dominic Fortes. Check the alignment of the rainbow with respect to the trees in each of the ...


9

engineer already answered it completely, I only want to add that the question is completely valid even if you already know that separation of wavelength occurs. The thing is, some materials are practically opaque or too much transparent (refractive index is equal to that of air and no separation occurs) in infrared and ultraviolet while transparent in the ...


8

As you say, a changing magnetic field is always associated with a changing electric field, and in fact in relativity they are finally revealed to be the same field. So at this level it cannot be said that the one field generates the other, as they are merely two aspects of the same object. But maybe you still want to look at it from the perspective of ...


6

This plane polarized wave from wikipedia may help Electromagnetic waves can be imagined as a self-propagating transverse oscillating wave of electric and magnetic fields. This 3D animation shows a plane linearly polarized wave propagating from left to right. Note that the electric and magnetic fields in such a wave are in-phase with each other, ...


5

Is it possible that rainbows have ultraviolet bands and infra red bands and we are not able to see? Yes, see engineer's answer. As for whether we can see them, take a look at aphakia: "Aphakic people are reported to be able to see ultraviolet wavelengths (400–300 nm) that are normally excluded by the lens. They perceive this light as whitish blue or whitish ...


3

Classically (since rob has done a thorough job on the quantum picture), the amplitude of a light wave is not related to any physical extent. It is not the size of the wave in space, it is the strength of the fields (electric and magnetic). We often draw wavy lines, but if you look closely the transverse axes will be label differently for, say, waves on a ...


3

I used to make X-ray tubes for a living... and the "right" answer to this question would run the length of a book. So just a few pointers. I don't expect that you would be able to create an electron tube after this - at least not one that lasts. Note also that if you do get it to work, it will produce dangerous (X ray) radiation. And unless you understand ...


3

The water droplets that create a rainbow are not emitting the light that you see in a rainbow; if they were, you would see a glowing cloud of consistent color, not a rainbow. The rainbow is formed by sunlight refracting and reflecting through water droplets in the air; the water refracts through the "front" of the drop, reflects off the "back," and refracts ...


3

"a changing magnetic field is not generated by a changing electric field, but instead just happens to always be present perpendicular to a changing electric field due to the laws of electromagnetism." So ... it is due to but not caused by. What is the difference? Short answer: it is not only "a thing" it is a correct thing. This is much more clearly ...


2

Maxwell's equations in vacuum are: $$\nabla\cdot\mathbf{E} = 0$$ $$\nabla\cdot\mathbf{B} = 0$$ $$\nabla\times\mathbf{E} = -\frac{\partial\mathbf{B}}{\partial t}$$ $$\nabla\times\mathbf{B} = \frac{1}{c^2}\frac{\partial\mathbf{E}}{\partial t}$$ It's the last two of these that give rise to the interpretation that a changing magnetic field generates an electric ...


2

there are other parameters like the number of free electrons in the atoms of the material, atomic size etc. Close. While density of particles does matter, it also depends on the material property. More precisely, it is closely related to how the electrons react when situated under electromagnetic oscillation. Each bound electrons has its natural ...


2

Coherency of light in practice is not an either/or issue. Any light due to any source has some degree of coherence. Laser light has usually much higher coherence than light of a hot metal filament. Some degree of coherence means, in simple wording, that light waves at one point of space due to different parts of the source behave similarly (they have ...


2

Note that $e^{jx} - e^{-jx} = 2j \sin(x)$ So what you have written is not an electromagnetic wave at all. It is an electric field with a fixed direction and an amplitude that varies sinusoidally along the z-axis. Of course if you multiply this by $e^{j\omega t}$, then you do have a wave. Given the wording I suspect you are meant to assume this (though I ...


2

Has this problem been solved since? Not in the sense Feynman meant. Approximate way to describe action of one charged part of body on another is known since Lorentz - the so-called Lorentz-Abraham-Dirac term. What Feynman is getting at is this term works somewhat, but leads to contradictions when pushed to its consequences. The problem of self-action ...


2

If you twisted my arm and forced me to assign an amplitude to a single photon, I'd do it this way: The energy density of a classical electromagnetic field is \begin{align} U &= \frac12 \left( \epsilon_0 E^2 + \frac1{\mu_0} B^2 \right) \\ &= \epsilon_0 E^2 &\text{(only for light in a vacuum)} \end{align} where $E,B$ are the amplitudes of the ...


2

In the context of ion beams, space charge is the tendency of the beam to expand transversely (perpendicular to the direction of the beam's travel) due to the mutual repulsion of the ions in the beam. All the ions have the same sign charge, so they repel. The name "space charge" comes from plasma physics where is is often computationally easier to treat the ...


2

It's tempting to think of photoionisation as the photon coming in like a billiard ball and knocking out an electron. However this is a very misleading representation of the process. A gamma ray is poorly modeled as a photon or photon(s) because the energy in it is delocalised. If you wanted to use a photon description you'd have to treat the ray as a ...


2

There are three factors that need to be considered across all wavelengths: (1) the ability of the water droplet to refract and disperse the incoming light, (2) the ability of the eye to sense the wavelength, and (3) the ability of air to transmit it. The visible range we 'see' in a rainbow with our eyes satisfies all three. UV , depending on how short the ...


1

Firstly, I would like to say that there is no particular terminal separation between negative charges and positive charges. Actually you will understand it better if I would clarify in this way that scientists first saw that having even follow the same statistical distribution i.e. Fermi Dirac distribution some of them actually repel others and some do ...


1

you can draw feynman digrams and then calculate scattering amplitudes and it is in the non relativistic limit is proportinal to potential.so if the potential is positive it means they repel. this sort of claculation is done in peskin book and A.Zee book.in peskin book page no 125. this is the most rigorous work to prove gravity is always attractive. by ...


1

Because observations made by physicists have found that this is what nature does.


1

No. As has been said, the raindrop is not emitting the light, it is just acting as an optical device that deflects light emitted by the sun. However, the spectral lines you would expect to see in sunlight refracted by a prism will not, repeat NOT, be seen. The mechanism that produces rainbows is very different than the mechanism that produces a spectrum ...


1

The answer to As an electron drops from a higher energy level to a lower energy level, can it be modeled as a the continuous movement of a charged body, therefore causing a magnetic field to be generated around it? is "Yes, but only trivially." That is, you could probably work backwards from the far-field radiation to some imagined moving source ...


1

It's not really worthwhile in this type of situation. (It makes sense in other situations however ... like transferring power from the ground to an airplane or satellite.) The two most plausible system types are: (A) Microwaves / radiowaves: Emitted by an antenna, collected by a rectenna (B) Visible / infrared: Emitted by a laser, collected by a ...


1

Do the electric and magnetic components of an electromagnetic wave really generate each other? No they don't. Like Andrea said, they're two "aspects" of the same thing. And like you said, it's an electromagnetic wave. See the wiki article for electromagnetic radiation where you can read that "the curl operator on one side of these equations results in ...


1

is my interpretation of the dynamics of the self-force correct and is there a physical or intuitive explanation for this extremely pathological behavior in the presence of a Coulomb potential? Eliezer makes his argument based on the equation with the Lorentz-Abraham-Dirac term. This term was originally (Lorentz) devised as an approximate way to account ...


1

Electric and magnetic fields themselves are totally uncharged. They are always described as totally uncharged things. They can either be described as two uncharged fields (when treated in the more traditional formulation) or as aspects of a unified electromagnetic field. In both descriptions the field(s) interact with charged things without being charged ...


1

The reason we see an interference pattern on a screen is because of diffuse reflection. This is because in diffuse reflection, the incident light can be considered to be absorbed and uniformly emitted out in all directions. This results in a brightness at a point proportional to the brightness of the incident light. A mirror, however, simply reflects ...


1

It looks like the answer is negative: ...


1

What I'm asking is, has someone measured, that at one moment of time the peak of magnetic component is in the same distance from source as the peak at the electric field. That should be not easy because this peaks are moving with c. You're asking the wrong question. Scientists don't measure the differences in the locations of the peaks of two signals. ...



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