# Tag Info

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What Vasily Mitch says is true (+1). But some objects are colorful because of interactions that take place over a larger region than a single atom. Metals reflect light because electrons spread out through the metal. They can easily move, which makes them conductive. Classically, the oscillating electric field in light vibrates the electrons, and vibrating ...

27

It of course depends on what you define as colour. If it is defined as the change in the visible spectrum of a light, then a single atom can definitely absorb a photon of a preferable wavelength and thus slightly change the spectrum of the passing light. Many atoms have excitation energies falling into the visible spectrum when atoms absorb the photons, ...

7

It depends on the solid. Molecular solids derive their color, that is their optical reflection or transmission, from the molecules that they consist of. The molecules stick together by van der Waals forces, which have only little impact on their spectral properties. Some solids, like quartz (glass), diamond, ruby, derive their colors from impurities. You ...

5

The shoes and shoelaces are made from different materials. The shoelaces contain a substance that fluoresces: it converts the UV light to blue light so that it becomes visible to you. The remainder of the shoes does not contain this substance, so it just absorbs or reflects the UV light, still invisible to you. There are many blue fluorescent substances, so ...

4

Fact 1. One cannot hold a nuclear reactor. What it needs to work is tons and tons of material, mostly for protecting people from radioactivity Fact 2. Even if technology could come to the point of making a hand held reactor , only a robot could carry it. Unless a lot of material would surround it the human carrier would be dead. Fact 3. The radioactivity ...

4

As Andrew explains, you will get halo effects rather than rainbows. There may be some colour but it is likely not very visible. This case may almost happen on Mars, since CO$_2$ crystals have cubical symmetry. Unfortunately the most likely crystals are cuboctahedra, octahedra and other shapes. Still, it is possible to simulate the halos they generate. On ...

4

You are confusing photons with electromagnetic waves, light. They slow down to 225,000,000 m/s in water with a refractive idex of 1.3, to 200,000,000 m/s in glass and to 125,000,000 m/s in diamond. So its speed can be varied with variations in the medium. This is not correct . Light,the electromagnetic wave, slows down. Light is made out by the ...

4

I've grown curious about the phenomenon of light interference. In the context of what you have written your use of the word interference is inappropriate and might be better replaced with the word superposition? In Physics the common use of the word interference is when light from coherent light sources overlaps. For example, for a two slit arrangement with ...

3

Here is another video about a UV camera from Veritaseum. The World in UV. It does not explain what you asked, but it does make something clear. The UV camera detects UV light. It then shows it to you with light you can see. That light is visible. So you can conclude that a UV camera is a UV to visible converter. To a degree, that is all you need to know. You ...

3

A ray is a continuous beam from a source to a point of interception. It is a path followed by billions of photons, each of which is associated with a wave packet of finite size and measurable energy.

3

It depends how you're defining "motion". As you're talking about photons as opposed to light generally, I'll talk from the quantum perspective rather than just classical waves. See these related questions for more on the different perspectives: Do photons actually slow down in a medium, or is the speed decrease just apparent? What is the ...

2

Classically, because matter is made of charged electrons and protons. An electromagnetic field or a disturbances in it exerts forces on charged particles. In particular, electrons are light and easy to push around. Quantum mechanically, one talks the same thing with energy rather than forces. Forces change the trajectory of a particle. One of the reasons ...

2

It's not quite correct to say that blue light is scattered to a maximum at sunset and other wavelengths are scattered the least. As far as Rayleigh scattering is concerned shorter wavelengths are always scattered more than the longer wavelengths and this amount stays the same at all hours of the day. Each particular wavelength of light experiences the same ...

2

You have to adopt a sign convention when defining the Fresnel coefficients. Usually you say that a positive reflection coefficient means the wave component tangential to the interface keeps the same direction. For s-polarised light that is the E-field, but for p-polarised light it is the H-field. Note that you cannot just say "the direction of the E-...

2

For "regular" (silicon-based) solar panels, I believe the answer is no. Silicon is an indirect band gap material. Recombination rarely releases photons, so an increase in conduction band electrons does not make the material glow. Likewise, an increase in valence band electrons does not make the material darker. Now if you had something like a ...

2

There is no evidence for "redness" in the sense of "perception or the sensation of red" outside humans (and some animals). There is plenty of evidence of photons with certain wavelengths that make us perceive red. The argument between Goethe and Newton is basically about "colour is subjective experience" and "colour is a ...

2

I am strongly of the idea that, as physicists, we should never forget that our theories are just that: theories. They are an attempt at a model which describes nature, but does not tell us exactly what nature is intrinsically. This model is as good as our measurements can be in the sense that an experimentally proven theory will be adequate as long as ...

2

This answer is based on general knowledge of physics and of some atmospheric phenomena, rather than specific calculations for the cube. The first point to say is that most shapes, including cubes, do offer prisms to light passing through. For example, consider a light ray entering one face and exiting an adjacent face. So there will be a net refraction for ...

2

Dheeraj, great volumes of stuff have been written about this, I recommend you do a search on wave-particle duality; in the meantime, here are the (simplified) basics. The basic unit of light is the photon. Depending on its wavelength and what method you use to detect it, it can behave either as a wave or a particle. If you have a very very large number of ...

2

You've come to a long time phyilosophical question: does a field actually "exist"? We cannot measure fields. There is no instrument able to measure a "field". The instrument you use to measure electric field is actually based on forces. The instrument detects an electric force and then it deduces the value of the $E$ field. In an empty ...

1

As others have mentioned, physicists have studied higher dimensional theories to explain light and other phenomena, and it's certainly possible that some of these will eventually provide better explanations than the theories we have now. To address your first question about how "correct" our current theories are, they are very good; nearly every ...

1

The diagram is a bit misleading. The intensity variation due to diffraction at an edge is as follows, and what you might see on a screen even with a laser pointer and a razor blade edge. The extended lines are light which has been reflected off the edge imperfections.

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Color vision is based on the response of cone cells in the eye to different frequencies of light. For humans (with full color vision) there are three types of cones sensitive to different frequency ranges at different levels. Each individual photon in your superposed wave will be of a specific frequency, which for your question you've assumed is outside ...

1

So in that sense, what scientific evidence is there for the definable real world quality of redness independent our perception? The atomic spectra evidence, they have specific frequencies for specific colors perceived by our eyes. This is the electromagnetic spectrum as a function of the wavelength/frequency . Visible light is a very small part of the ...

1

In addition to @ProfRob’s answer, I’ll just point out that refractive index is in general a complex number. And, the Fresnel Equations apply to complex refractive index too. So the answer is: You’re right, the reflection phase is not always $\pi$. In principle, it can be anything!

1

Let's make a simple estimate. The energy density of an electric field is $$\rho_E = (1/2)\epsilon_0 E^2.$$ This corresponds to a mass density $\rho = \rho_E/c^2$. If we consider a million volt per meter field across a cubic meter volume we get the density $\rho=4.9258\cdot 10^{-17}$ kg/m$^3$ - far less than the 1 kg of air in a cubic meter. If we go up to \$...

1

The gravitational effect of something like an electric field includes a contribution from the energy density of the field, and a contribution from the pressure or tension in the field. Sometimes these contributions can cancel each other out, so one would not necessarily expect light to be bent by the gravitation associated with an electric field. For example,...

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Short answer: Let's say that interacting means transferring energy and/or momentum between two systems. Our systems are light and matter. The interaction is possible because the light is an EM wave (both in classical and quantum schemes) that have this property: transports energy and momentum. Long answer: Let's see how this works. A system is described ...

1

Perhaps this question is answerable in a purely classical electromagnetic wave setting. You need to be aware that there are different definitions of "speed" for waves. The speed of light is a "phase velocity", which is not really a velocity (see below). The phase velocity is more the ratio between frequency and wavelength. Both are ...

1

I understand that EM waves are self-perpetuated due to the interactions between changing electric and magnetic fields as described by Maxwell's third and fourth equations, but I'm stuck conceptually on what they are if there are no electrons or conductors around. people were stuck like you begininning of the 20th century thinking the EM waves required a ...

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