# Tag Info

4

With photons the physical attributes of the pattern are connected to the frequency/energy of the emitted light, which is a wave with wavelength in 400-700nm, right? Yes, with photons the double-slit pattern is not surprising, since photons are excitations of a specific mode of radiation and the modes obey the usual classical wave equation, which of course ...

3

As mentioned in comments, a photon is "delocalised", so it feels the whole system. You may imagine a photon as a long-long wave (to have a defined frequency) and as such it interacts with the whole material. More strictly, one can say that the source of photon is the whole set of charges, so the photon is a collective mode of excitation of a given system. ...

2

In general, what you would need to know to completely calculate the situation through, is the wavelength-dependent absorption of your plastic and water and the characteristics of your LED (wavelength, spectral broadness, etc.). And yes, in general, most plastics have IR-absorption (which is why IR spectroscopy is used in plastic analytics). But depending on ...

0

Light as a Particle The photons in the beam of light are continuously being absorbed and re-emitted by the glass atoms (though this is also true in the other mediums light slows in). The level by which the light is slowed is dependent on how often this happens. As @garyp commented below this question, the delay also depends on how long the photon stays in ...

4

The answers given here make me wonder, because I sense in here perhaps a misunderstanding. Or maybe I'm wrong, which might be more likely. :-) The answers here refer to distances light travels. But as far as I understood, light is never slower than 299 792 458 m/s. I guess it may "look" like from a point of reference that light has slowed down, when a event ...

-2

How would you define speed? In case it has a direction: The maximum slowdown you can get is 2C, this is achieved by using a mirror. In case it is defined by the time taken to get from A to B In case you would define speed by looking at the width of an object, where the light enters at point A, and leaves at point B, the following can be derived: The ...

18

The short answer is that there is no known theoretical strictly positive lower bound to the speed of light. Any positive number, no matter how small, is possible, although limits are set for each candidate material, as I explain at the end of my answer. One has to be pedantic to understand the lack of limitation to a more generalized "speed of light". From ...

16

How the light slows down in a matter, it depends on the recipe of its refractive index. For common, ordinary materials it is in the range of 1-3. Bose-Einstein condensates have an extreme refractional index, even millions or billions. In a BEC with a refractive index of $10^9$, the speed of light is only $30~\mathrm{cm/s}$. Here is a relative old article ...

3

As in ptomato's answer optical path length is generally expressed with units of length. However, a related quantity is optical path difference for a system or rays, which measures the degree of optical aberration (not to be confused with stellar aberration). Optical path difference is the RMS deviation of the optical path length of rays through a system's ...

2

Optical path length generally has units of length, as its name implies. I haven't seen the dimensionless quantity $OPL/\lambda_0$ referred to as optical path length.

0

@Flojo1 - I know more about RF atmospheric refraction than optical, so this won't give you anywhere near a complete answer. But I can say a few things that may be of some use. First, looming is no more than enough vertical refraction in the earth atmosphere that an object on the surface looks like it is above the surface. Sinking is the opposite. There's ...

0

First: refrative index of air $n\approx 1 \neq 0$, let's say $n=1$. Now we take $12cm/km$ "bending" of light which results in $\beta = \arctan\left(0.12/1000\right) = 0.006875^\circ$. That is small... Now we say a small differene in air density results in change of the refractive index of $\Delta n = 0.000392$ and we have $n = 1.000392$, thus the incident ...

0

To get a real image you need to have the object distance $u$ greater than the focal length of the lens $f$. If that condition is satisfied then if $u<v$ where $v$ is the image distance, the image is real, inverted and magnified. For every combination of object distance $u$ and image distance $v$ there is another combination of these distances which form ...

0

To understand this fully, you really need to be thinking of rays as normals to wavefronts. In this representation, a ray's tail gets assigned by a phase factor to represent the total phase of the plane wave. This phase factor advances by $2\,\pi\,\times$ an amount calculated by multiplying the distance advanced along the wavefront, in wavelengths, by the ...

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