40 votes
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Why are the edges of a broken glass almost opaque?

Because you're looking through more of glass I'd like to just add to the other answers with some diagrams. We have an intuition that light beams travel in straight lines, so we tend to assume that the ...
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38 votes
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Why don't opaque objects reflect light?

The question is asking "which of the following objects will you not see a reflection?". A distinction (albeit poorly) is being made between specular reflection and diffuse reflection. The ...
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37 votes

Why are the edges of a broken glass almost opaque?

Have you ever noticed that at the aquarium, sometimes the thick glass tanks carrying fish appear green? Glass is made of silica and lime but sometimes it carries impurities, like iron oxide, that ...
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30 votes

If we repeatedly divide a colorful solid in half, at what point will the color disappear?

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 ...
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29 votes

Why don't opaque objects reflect light?

In my opinion, one more thing which is possible here is that may be the question is Which among the following causes diffuse reflection ? Undisturbed water can also give specular reflections but the ...
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  • 6,884
28 votes

If we repeatedly divide a colorful solid in half, at what point will the color disappear?

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 ...
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22 votes
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Why is diamond transparent while graphite is not?

The answer lies in the band structure of the two materials. The band structure describes how the electrons in a solid are bound, and what other energy states are available to them. Very simply, the ...
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17 votes

Why don't opaque objects reflect light?

There are two main types of reflection: specular (polished metal, mirror, undisturbed water) In the case of specular reflection, the surface is on a micro level so smooth, that it is able to reflect ...
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16 votes
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How can the refractive index be below 1 in a dielectric?

What you are describing is anomalous dispersion. This happens when a material becomes strongly absorbing, typically near an absorption line, and the refractive index becomes complex. In these ...
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16 votes

Why don't opaque objects reflect light?

Yeah, clearly this teacher regards the following two as synonymous: 'mirror reflection' and 'reflection'. Presumably this teacher is unaware of the possibility/existence of diffuse reflection. This ...
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9 votes
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How do non-mechanical solid-state optical switches work?

It looks like there are at least two ways to go about this: Bistable MEMS MEMS (Microelectromechanical systems) are very small structures, with features from $1-100\mu m$ in size, generally made with ...
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  • 283
7 votes
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Are special relativity calcs affected by media?

No, because in a dielectric medium light isn't light, and that's why its speed isn't $c$. The speed of light in a dielectric medium remains unchanged. You'll find lots of questions discussing exactly ...
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7 votes
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How do "see through mirrors" work?

One way mirrors are just semi-transparent mirrors with a little trick. The laws of thermodynamics prevents a "real" one-way mirrors from existing; if they did exist, then we can put two rooms at the ...
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  • 645
7 votes

If we repeatedly divide a colorful solid in half, at what point will the color disappear?

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 ...
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6 votes
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Can you burn invisible jelly balls with a laser?

It appears that the questioner wants to know if a laser can burn the jelly balls in water even though they are invisible in the water due to having the same refractive index. The answer is "yes". ...
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6 votes

Why can't ultraviolet light pass through glass?

It depends on what your "glass" is made out of. If you work in a chemistry lab, it's common to use cuvettes made of pure quartz, SiO2, which has a bandgap of 10.2 eV and will very happily pass ...
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6 votes

Why are the edges of a broken glass almost opaque?

These can be the reasons: First of all, when you broke your specs, the edges became uneven so they(light rays) can't penetrate the glass properly. Due to which the light rays got reflected away by ...
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  • 817
5 votes

Diameter of a lens vs Diameter of the circular Aperture of the lens vs Aperture of the lens

The diameter of the lens is its physical diameter. It is sometimes advantageous to reduce the area through which the light travels and that is then the aperture. In the case of resolving power ...
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5 votes

What does the refractive index for e.g. alpha mean?

The Greek letters are not related to wavelength but to the directions in crystals. In anisotropic crystals the speed of light (and so the index of refraction) depends on the polarization of light and ...
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5 votes
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Can light in a medium travel faster than speed of light $c$ in vacuum?

The index of refraction can indeed be less than $1$. This means that the phase velocity of light can exceed $c$ (the vacuum speed of light), and in fact it does exceed $c$ over a large range of ...
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5 votes

Are there any real-world examples of refraction of light by magnetic permeability?

Short answer is no. In that wavelength range, the effect of the magnetic polarizability is almost always much less than the electric polarizability. So even though the index of refraction is defined ...
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4 votes
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Why does aluminium-on-glass mirror work without distortion?

Let us take the example of the Hubble primary mirror. It has a diameter of 2.4 m and a mass of 828 kg. It is actually made in a sandwich structure - glass-honeycomb-glass - making it about 30 cm thick ...
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4 votes

Can a mirror reflect only one color while allowing all other visible light pass through?

You could look at Optical coatings and dichroic filters. Optical coatings are many thin layers of material of two of more different refractive indices, about one light wavelength in thickness. They ...
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4 votes

Properties of light and refractive index of materials

The refractive index is defined by the ratio $$n=\frac{v}{c},$$ between the speed of the light in the medium and the speed of the light in the vacuum. From the wave equation we read the velocity $v$ ...
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4 votes

Can you burn invisible jelly balls with a laser?

There are transparent things at any wavelength, and everything is intransparent at some wavelength. Cutting of 'clear' acrylic or glass happens at wavelengths that are strongly absorbed in those ...
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  • 110
4 votes

Why doesn't infrared radiation pass through objects?

In the case of conducting objects, it is because free charge redistributes to diminish the electric field, up to the so-called plasma frequency of the material (metal reflects light and infrared, but ...
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  • 9,025
4 votes

Meaning of circularity in phase retarder definition

The circularity is not redundant, because retarding the relative phase between components along two spacial axes is not the most general thing that can happen in these materials. A more general ...
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  • 1,564
4 votes
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Reason for particular pattern of clouds near sun

If the cloud density is constant, it seems denser near the horizon, because there are more clouds for the same angle of vision. The fact that the sun is near the horizon turns clouds brighter in that ...
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4 votes

Could we see through objects if our eye could detect other wavelengths of light?

We can already see through objects like glass. Colored glass transmits certain wavelengths and not others. If our eyes could see more wavelengths than presently this would be no different . For ...
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