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8

In fact the light is not split up like in a rainbow or a prism. The colours appear due to thin film interefence - see e.g. http://en.wikipedia.org/wiki/Thin-film_interference The thickness of the petrol or oil is similar to the wavelength of visible light, which is about 380 to 750 nm or 0.38 to 0.75 $\mu$m (- or about 500 atoms think). Different colours ...


7

The solution boils down to examining what is meant by the term instantly in: "If I turn the light off in a room why does the light instantly disappear" All of the visible photons in the box cannot instantly disappear since the information about the source going out only travels at finite speed $v\approx c_\text{vacuum}$. Once the source stops ...


5

There are several terms with precise meaning in physical sciences that have been pulled into common language and misused. Opaque however does not appear to be one of them. According to several etymology sources I just looked up (like Etymology Online for example) it appears to have rather mushy origins in Latin and French meaning darkened or shady. For the ...


5

There are two questions here. The first - "what is the definition of opaque" is terribly broad and depends on the field / context. I will focus on the second: when and how does a body let radiation through? We should really ask the converse question: by what mechanisms does a body stop radiation from going through. I will answer this for different parts of ...


4

It may be useful to start this explanation from the origin of a light wave: an oscillating charge. Start with the idea that a stationary charge is surrounded by an electric field, then imagine wiggling that charge up and down. Now the field lines will turn to wiggles instead of straight lines. Those wiggling field lines are the electromagnetic waves we call ...


4

A picture is worth a thousand words. Here's how it looks as a function of space, evolving in time: Here blue is real part, and purple is imaginary part of the complex exponent $\exp(i(kx-\omega t))$. If you instead just look at $\exp(-i\omega t)$, you'll get this:


4

The electromagnetic field itself contains energy distinct from the energy of charged bodies, the energy in a given volume of empty space can be found by integrating the energy densities $\frac{1}{2}\epsilon E^2$ and $\frac{1}{2} \frac{B^2}{\mu}$ over the region. When the EM fields increase the kinetic energy of charged particles, there is a corresponding ...


3

Acoustic waves travel through a medium (air, water, metal, etc), there is no known medium through which light travels Both the speed of sound and the speed of light have fixed values regardless of the speed of their source Acoustic waves can be longitudinal (in gases) or transversal (in solids) whereas light is only transversal. You can measure acoustic ...


3

The answer would appear to be "Yes", at least in theory. A "kugelblitz" is a concentration of light so intense that it forms an event horizon and becomes a Black Hole according to general relativity. It would be a BH whose original mass-energy had been in the form of light rather than matter.


3

The light we see with our eyes is electromagnetic radiation, very well modeled by Maxwell's equations. 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 ...


3

Optically speaking, and very simply: An opaque material permits no light to pass through it. A material which passes light but does not pass image detail is called translucent. A material which passes light AND image detail is called transparent. "Passing light" technically means ANY light, but in practice some materials pass so little light that they ...


3

The problem I think you are having is that once you assume a false statement, you can prove anything. So everything you said in the second paragraph is true if you treat the problem classically. You are right that each electromagnetic standing-wave mode in the cavity would have no energy, and so there would be no electromagnetic energy at all even at finite ...


2

Your single photon pulse wave function is an element of the first Fock layer (the zeroth is the vacuum layer) of the quantised Maxwell field Fock space. The electric field is still an operator but you can obtain its expectation value as $<E>=<ψ|E|ψ>$.


2

According to Maxwell's theory of electromagnetism, a light pulse (or generic electromagnetic wave) carries momentum, which can be transferred to an absorbing surface hit by the pulse. This momentum transfer is known under the name 'radiation pressure'. Despite carrying momentum, light carries no mass. Yet a light pulse does carry energy. For a light pulse ...


2

If photons transmit the electromagnetic force, which is observable: the photon or the electron? Do we ever directly measure a photon, or do we only measure it's effect on electrons. For example suppose I shine a laser at a wall Let us clear up that photons ( and also electrons) are quantum mechanical elementary particles, and classical electromagnetic ...


2

The electron on an atom gets excited to a higher level when some how the energy is transferred to the electron. But I can't understand it. The way we currently understand in physics this interaction is exactly like that: a photon transfers its energy to the atom and as a consequence one of the electrons goes to a corresponding exited state. And this can ...


2

Probably the most direct example is synchrotron radiation. This is the case in which an electron is accelerating by moving in along a curved path (e.g., a helix). As it is accelerated, it emits photons in the radio spectrum: (source) Another big one would be bremsstrahlung in which an electron moving along a path is decelerated near the presence of a ...


2

Since this was not stated yet, I would just like to give my stance on it. All fundamental particles can be seen as excitations of fields. This is true for photons, electrons, neutrinos, etc. Do these fields need a medium in which they propagate? Not as far as we can tell. Everything we see and experience are excitations of these fields, a single one of ...


2

There are several ways to lose signal strength: Geometric dilution As you have mentioned, if the beam spreads out, it distributes a fixed amount of intensity over an ever increasing surface, so the radiance (intensity density) decreases. The signal loss behaves like a negative power law (depending on the dimension of spreading $1/R^2$) Absorption If ...


2

Two parts to this answer - "near field" and "far field". When you have an parabolic antenna, or in general any source that is not a point source, you can shape the beam to follow something other than a simple $1/r^2$ relationship - as you pointed out, a laser beam can be created in a way that you can "collect" all the energy (and assuming no absorption in ...


2

They control the spectrum with regulations: Below is the diagram of frequency allocations in the united states. When people think of radio, they typically think of only the FM or AM parts of the spectrum. However, any frequency of electromagnetic radiation can be used to communicate with others. There is nothing that a government can do that could ...


1

The wiki article you quote is succinct, the photon is an elementary particle in the table of elementary particles of the standard model of particle physics. It is a quantum mechanical entity which means it is described by a wavefunction whose square gives the probability of finding the photon at (x,y,z) at time t. The double slit experiment with a single ...


1

Acoustic Wave is a wave in which motion of one atom causes motion of another atom because it is lying next to it. Light is change in electric or magnetic field which further causes changing fields.


1

90% of Astrophysics is to do with electromagnetic phenomena. Bar neutrinos or directly grabbing stuff in our own solar system, there's not much else you can do but observe the electromagnetic radiation coming from out there. Your question is therefore massively broad. But here are some examples you could research. Rayleigh scattering observed in the ...


1

When you change the free field $A_\mu$ by means of a gauge transformation, you can easily see that it affects longitudinal and timelike degrees of feedom. Since observables are gauge invariant, those degrees of freedom cannot be physical.


1

If you look at a wave at a moment in time, you can see how it varies spatially by plugging in different values of r: $e^{ikr}$. If you look at a point in space, you can see how it varies in time by fixing r and varying t: $e^{-i\omega t}$. If you want the behavior in both space and time, you end up with the expression you have - and you can see how the ...


1

The Result You Seek The Wikipedia page on angular momentum of light gives the classical angular momentum as: $$\frac{\epsilon_0}{2i\omega}\int_{\mathbb{R}^3} \left(\mathbf{E}^\ast\times\mathbf{E}\right)d^{3}\mathbf{r} +\frac{\epsilon_0}{2i\omega}\sum_{i=x,y,z}\int_{\mathbb{R}^3} ...


1

Einstein once compared the photon with a famous person (sorry I forgot the name) who changed confession at young age and returned to its initial confession before he died: Light behaves as a photon at the starting point and at the end point, and it behaves like a wave during its travel. By the way, the light wave is not going up and down, it is not a ...


1

That the phase speed can have a dependence on the wavelength/frequency of the wave. For instance, a whistler mode wave can have a cubic dispersion relation at low frequencies. In this limit, the higher(smaller) frequencies(wavelengths) propagate faster than the converse. It results in a sort of "spreading out" of the wave modes. This if often seen ...


1

In a very short time, a light beam can bounce around the room many times. Each time it hits a solid surface a fraction is absorbed and the rest is reflected. It is either absorbed mostly by walls, floors and ceiling or bounces out the window faster than the eye can see. It does have a small role in heating the room and thus contributing to the IR ...



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