Tag Info

New answers tagged

1

This is late, but your intuition was correct. The amount of pressure imparted on both mirrors is multiplied by the number of times the light bounces, ignoring redshift. In practice, this doesn't mean you get infinite thrust, because no two mirrors can reflect 100% efficiently, nor be perfectly aligned. However, the idea still works, and there is actually ...


0

Since two wave aren't not coherent (i.e, different frequency), they cannot intefere with each other.


3

Further Conifold's Comment: "Electromagnetic field is self-propagating, changing electric field creates magnetic field in its surroundings, and then magnetic field does the same for electric field. Original theory was that electromagnetic field propagated in ether, but properties of ether had to be made paradoxical to account for observed behavior, so ...


0

Gravity can change frequency. A light beam going towards a massive body is blue-shifted by the gravitational field. If it is escaping a gravitational body, then it is red-shifted.


2

The photon is an elementary particle. There are two ways do measure the frequency and therefore the energy of the photon since its energy E=h*nu . 1) using a diffraction grating which analyses the wavelengths in a beam of light , as below: This is the spectrum of iron. Each line is composed of zillions of photons with that frequency. If one sent one ...


0

In regards to your question: Can the frequency of light change in propagation from one media to another, the answer is no. I found a previous response to a similar question that might help you: Think of it like this: At the boundary/interface of the medium, the number of waves you send is the number of waves you receive, at the other side, almost ...


0

Ultraviolet light is very high energy. When it makes contact with your skin, you can actually break chemical bonds.


1

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


0

There are many different levels of explanation for this question. Strangely enough most of them will dive into quantum electrodynamics, Feynman diagrams and exchange of virtual photons... I will try a simpler path that still carries some explanation. When you put two charges at a distance, they deform the -- otherwise flat -- electromagnetic (EM) potential ...


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

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 ...


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 ...


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 ...


6

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 ...


46

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 ...


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 ...


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 ...


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 ...


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 ...


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 ...


0

The problem is that your reference frame is not inertcial so you can't applay the physics valid for a inertial system. A charge accelerating with respect a inertial system radiates according to maxwell's equations which are valid for an inertial sistem. You just can't simply apply maxewll's equation in an non inertial frame.


0

Turns out that due to orthogonality relations of Hermite-Gauss poly's, Hermite-Gauss modes are orthonormal, so $$ \int \int u_{n,m} \left(u_{n',m'}\right){}^*dxdy=\delta _{m,m'} \delta _{n,n'} $$ Then a's can be found by multiplying both sides by conjugate of u and integrating ...


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

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 ...


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

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 ...


0

The skin depth becomes smaller as the conductivity increases because the Ohmic dissipation of the wave energy increases. The current density is given by $\vec{J} =\sigma \vec{E}$ and the work done per unit volume by the fields in moving charges in the conductor is $\vec{J}\cdot \vec{E} = \sigma E^2$. The attenuation is in the direction of propagation of ...


0

Firstly, I think you've confused several points in your analysis of the situation. Working with the first picture, by standard electrostatic analysis, we see that there must be a standard Coulomb force between the plates for all times $t\ge t_2$, not just at $t=t_2$. This point is not too important, but I thought I'd mention it. Continuing to work with the ...


0

But it seems to me that the EM momentum it radiates in each direction is balanced by an equal amount of EM momentum radiated in the opposite direction. Is that true? It is true in the frame where the particle is at rest when it produces the retarded radiation. In other frames, particle moves and its angular pattern of Poynting intensity of radiation is ...


-1

I believe that the photons of EMR "escape" the source of them (excited electrons), whereas somehow the photons in a magnetic field just circle around.


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 ...


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 ...


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 ...


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 ...


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 ...


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

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 ...


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, ...


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 ...


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 ...


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 ...


1

Is light a particle which has a electromagnetic field around it OR does the particle itself travels in a wave like motion? The latter. Light consists of electromagnetic waves which have a quantum nature, wherein we say the photon is a quantum of light. This tends to get converted into a "particle" of light wherein people think of the photon as some ...


1

Is light a particle which has a electromagnetic field around it OR does the particle itself travels in a wave like motion? This depends of what you want to calculate. For atomic processes one use QED and photons are disturbances in EM field existing everywhere. But really one calculate processes in atomic and subatomic dimensions. If one want to ...


1

An RF cavity is just a resonator where the Electro-Magnetic field can oscillate. Physicists and engineers typically design those so that the fundamental mode (the stronger one) have a longitudinal component of the electric field that can accelerate the beam. This is a matter of solving the Maxwell equations with complex boundary conditions. There are many ...



Top 50 recent answers are included