# Tag Info

7

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 same temperature on the two sides of it. Then the radiation from one side will pass through but the radiation from the other side will be reflected, created a ...

6

You have just shown the effect of spherical aberration. Here is an accurate drawing showing that even when parallel to the principal axis rays after reflection do not meet at a point. Here is an example which you may see when having a drink and a caustic is produced.

5

Reflection is a form of scattering, but it is coherent scattering. When scattering occurs from a lot of identical particles rigidly fixed in a plane, then all the possible ways a single photon can be scattered from the plane of particles are fixed in phase. That is coherent scattering, and it is reflection. If the particles instead are, e.g., in a gas, ...

4

The thing is that there are no really good mirror coatings. From this plot from Edmund Optics, a reseller for technical optics, you can see that for 1-1.5 µm (telecommunication wavelength) the reflectance doesn't go higher than 98% (that's normal incidence, it will be a little higher for grazing incidence). In contrast, the inner surface of a glass fiber ...

3

This seems counter-intuitive, since the metal's electrons could interact with the electric field component of the EM wave and absorb it. In quantum mechanics light is emergent from zillions of photons, and photons as quantum mechanical particles have interactions with the spill field of the lattice that composes metals and (all other solids). It so happens ...

3

The trick with invisibility is to arrange the flow of light so that when someone looks towards you they see whatever is behind you. This can be achieved by two methods: either a chameleon-like rapid colouring and patterning of your clothing to make it look like the scenery behind---with a 3d hologram-like effect for the best results. a powerful lens-like ...

1

Color is a double valued concept, different in physics and in perception. In Physics there is a one to one correspondence between color seen in the visible spectrum and the frequency of light. Electromagnetic spectrum with visible light highlighted The whole electromagnetic spectrum covers many frequencies above an below the visible, which are the ...

1

It is true. There is nothing wrong with the diagram. A large spherical mirror will not give you a perfect image.

1

Your waveform would be a square wave with the lowest frequencies (those lower than the dish's cutoff frequency) missing. On an oscilloscope it would resemble a steady train of sharp spikes, each of very short duration. The frequency of those spikes would be equal to the harmonic series required to construct the square wave. You can simulate this scenario ...

1

The limiting factor for focusing light in this way is actually not the mirror's material properties but the quality of the grinding of the mirror. To focus light on a point, the mirror must be nearly a parabola (it would need to be a parabola if the sun was infinitely far away... but practically speaking, it's far enough away to treat it as infinitely far). ...

1

White textiles and paints have added materials, such as TiO2, to scatter light which results in diffuse reflection. I'm not sure about your use of the term "emission."

1

The normal explanation is that if the ring is massless then by Newton's law the slightest force acting on it along the rod will create infinite acceleration. What that really means is that the the string will always be normal (at 90') to the rod. In terms of the incoming and outgoing waves we usually write:  \frac{d}{dx} [ \sin(x-vt) + c \sin(x+vt+\phi) ] =...

1

Your answer is not completely correct. However, you are correct that we have to use the Floor Function (sometimes called the Greatest Integer Function) in case of a fractional value. \begin{array} {|c|c|c|}\hline \rm Value\ of(\frac{360°}{\alpha}) & \rm Position\ of\ object & \rm No.\ of\ images\ formed \\ \hline \rm Even & \rm Symmetric &...

1

I think the main reason is practicality. In the normal process of manufacturing of optical fiber, the material is simply pulled out of the preform, and the core and the cladding result directly from this (having been formed in the preform before pulling). If a mirror surface were used instead of low-index cladding, you'd have to find a material that would: ...

1

You are right that there are ample electronic transitions in a metal that match the frequency of optical and lower frequencies. However these transitions do not satisfy momentum conservation. When you apply a grid then momentum is only conserved up to an inverse lattice vector (of the grating). For a suitably choice of grid pitch and duty cycle it is then ...

1

For metals, whether an electromagnetic (EM) wave is reflected or absorbed is determined primarily by (1) the frequency (or wavelength) of the incident wave, and (2) the density of electrons in the material. This is a consequence of both (a) the response of free electrons to the electric field of EM radiation, and (b) Coulombic forces between these electrons ...

1

Technically, when we say that the light rays meet at infinity, it basically means that they never meet at all. This means that the light rays will never converge, and hence never form a real image. But the reality is a bit more complicated, and something that is not taught in school. Light behaves weirdly, both like a particle and a wave. Like a wave, it ...

1

In both cases, an electron absorbs and re-emits a photon. The difference is in the structure to which the electron belongs. In Rayleigh scattering by the atmosphere, electrons belong to molecules in a random (gaseous) structure in which each molecule moves independently from other molecules. The photon is typically re-emitted with its initial momentum, or ...

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