Questions related to the perception and measurement of light (primarily in the visible range), its mathematical description, the reproduction of colors by different means, color combinations, etc. Please use the tag [electromagnetic-radiation] if you want to refer to the general form of light.
-5
votes
3answers
186 views
Could some Red and Blue shifts be the result of light passing through “dark matter”?
As i see it, light behaves in certain ways, as the Double Slit experiement shows,
So when light comes into contact with dark matter, it becomes both a wave and a particle, the wave is bent around the ...
1
vote
0answers
66 views
Photon Statistics of a Coherent Gaussian Beam [closed]
Assume that a 100 pW He-Ne single-mode last emits light at 633 nm in a TEM00 Gaussian beam.
(a)What is the mean number of photons crossing a circle of radius equal to the waist radius of the beam ...
0
votes
1answer
160 views
Dispersion & Absorption in Optics
1) I understand light dispersion. But, I wonder what happens if I used a lens to focus it into a small point. Would it be a white point (would it reverse dispersion) or would I have a multicolored ...
2
votes
1answer
149 views
What's the difference between the equivalence principle and curvature of spacetime?
Calculating using the equivalence principle only accounts for half the deflection of light, whereas the other half is from curvature of space-time.
But isn't the equivalence principle the same thing ...
-1
votes
1answer
77 views
Determine when a light is going into the object [closed]
Please look at this image: (http://mypages.iit.edu/~smart/acadyear/refract.gif)
How can I determine when light is going into the object?
Actually, if there is, what is the simplest way to ...
2
votes
3answers
8k views
0
votes
1answer
403 views
Huygens Principle and principal of rectilinear propagation of light
Suppose I have an wave source and light waves are radiating from it. If I have a point source, then after a time t, with a radius of ct I will have a circular wave front.By Huygens principle each ...
0
votes
2answers
562 views
If nothing in the universe can travel faster than light, how come light can't escape a black hole? [duplicate]
Possible Duplicate:
How does gravity escape a black hole?
If nothing in the universe can travel faster than light, how come light can't escape a black hole? I mean, Einstein's relativity ...
1
vote
1answer
51 views
Where do the high order rainbows appear?
This site shows locations of the high order rainbows up to sixth order. My thought is that, There should be even higher order bows like 7th, 8th, etc. (Though they would be practically impossible to ...
1
vote
1answer
148 views
Speed of light and virtual particles
After becoming extremely bored while studying for an Afrikaans exam, I started thinking about virtual particles. So, can light (photons) interact with virtual particles (even though they only exist ...
2
votes
0answers
86 views
Bandgap Spacing in Photonic Crystals
I am doing some self-study on photonics and have encountered the following question:
We know that amorphous electronic crystals such as amorphous silicon have a bandgap. Can amorphous photonic ...
0
votes
1answer
62 views
Is synchrotron radiation considered incandescent?
Synchrotron radiation is produced via the acceleration of charged particles, much like incandescence.
However, all information I've seen state that incandescent light is produced exclusively from the ...
3
votes
1answer
88 views
What the name of the evacuated glass gadget with black and white vanes that turn when a light is applied?
I remember a glass device my physics teacher had at high school which
Contained some vanes mounted somehow on a vertical axis, which were all black on one side and white on the other
Was in a ...
13
votes
10answers
3k views
Why is light called an 'electromagnetic wave' if it's neither electric nor magnetic?
How can light be called electromagnetic if it doesn't appear to be electric nor magnetic?
If I go out to the sunlight, magnets aren't affected (or don't seem to be). And there is no transfer of ...
6
votes
2answers
481 views
Why do green lasers appear brighter and stronger than red and blue lasers?
This is mostly for my own personal illumination, and isn't directly related to any school or work projects. I just picked up a trio of laser pointers (red, green, and blue), and I notice that when I ...
0
votes
1answer
60 views
Dark light filters letting through less light
I'm looking for an explanation on why darker light filters let through less light than lighter filters (secondary/high school level). Although this seems to the layman like the obvious outcome, our ...
1
vote
1answer
76 views
Ideal four-level Gain Medium (or just any old gain medium)
What exactly is happening in a laser's gain cell when the irradiance is greater than the saturation irradiance?
Also can someone offer a clear conceptual treatment of the gain-coefficient and its ...
4
votes
1answer
197 views
why sometimes touching old flickering tube lights starts them properly
In my old house there are two old tube lights. Some times they don't start properly, (specially at evening time, may be it is because of low voltage), they starts flickering i.e. on and off ...
-1
votes
2answers
167 views
A light and magnetic mirror paradox?
If light is an electromagnetic wave and lightspeed is constant (we ignore spacetime or gravity for this question) why can't we slow down light with a few dozen wellplaced magnets and electricly ...
1
vote
1answer
45 views
Rays in Symmetric Resonator
I'm having some trouble figuring out how to get started on this question:
If I have a symmetric resonator with two concave mirrors of radii $R$ separated by a certain distance, after how many round ...
0
votes
2answers
376 views
Deriving the Poynting Theorem
I am trying to derive the Poynting theorem. So far, I've only been able to narrow down which equations I think I'll need to do so. These are the equations:
Maxwell's Equations:
$$
\nabla\times{\bf E} ...
0
votes
3answers
67 views
What kind of “camera” and “light” source should I use to detect the path along which the light moves?
I would like to have an image ( in any kind of space ), where I see the path of a "light" source. In my understanding the most common, directed source would be a laser pointer.
...
0
votes
2answers
145 views
Why is the sky blue? [duplicate]
Possible Duplicate:
Why does the sky change color?
Basically what the title says. What mechanisms are significant and how do they contribute to make the sky blue. Also when the sky is not ...
0
votes
2answers
313 views
Wavelength and resolution
I'm reading some texts that seam to assume knowledge of light that I'm not too familiar with. How does wavelength of light relate to the minimum distance span that can be observed (i.e. you cannot ...
3
votes
2answers
272 views
Why does light of high frequency appear violet?
When people are asked to match monchromatic violet light with an additive mix of basic colours, they (paradoxically) mix in red. In fact, the CIE 1931 color space chromaticity diagram shows this ...
0
votes
0answers
52 views
Electromagnetic charge [duplicate]
Possible Duplicate:
If electromagnetic field give charge to particles, does photon carry charge?
Is it possible to charge photons
I was wondering if light when it's in wave form (seeing ...
0
votes
0answers
27 views
Reflection of light [duplicate]
Possible Duplicate:
What is the difference between a white object and a mirror?
When I look at a red object under white light, I see it as red because it absorbs the other colours and ...
0
votes
2answers
240 views
Is there still light in practical darkness? Do photons penetrate everywhere?
I always thought that, even in darkness, there would still be some light, making complete darkness, i.e. complete absence of photons as far as I know, just a theoretical thing. When I tried looking up ...
1
vote
1answer
79 views
What would the spectral distribution of a greenbody look like?
Suppose you had a body that behaved like a blackbody for all wavelengths except some range that we would call "green". For those wavelengths it reflects all radiation incident upon it.
Am I just ...
4
votes
3answers
184 views
Is the number of rays projected by a source of light finite?
Take a source of light which gives out infinite number of rays, each ray with finite number of photons and each photon with a finite amount of energy,
Then, Aren't the number of photons become ...
2
votes
1answer
134 views
Solar energy and optical fiber
I'm not really good at science or physics, just wanted to ask about the idea (doesn't have an opportunity to test this).
Will this scheme work and what can be its efficiency?(The goal is to make ...
5
votes
4answers
428 views
What color would a proton be if it were visible to the human eye?
If a photon hits a proton, would it have a color? What color would it be?
0
votes
3answers
323 views
Liquid crystal shutter with >90% transmission?
Today's liquid crystal shutter glasses, when in the "transparent" state, exhibit only 40% light transmission.
They work using two polarizer layers, one which is liquid crystal and goes {vertical ...
2
votes
2answers
339 views
What's the Significance of Color Changes Between EM-Spectrums?
As everybody knows that Black objects are black because almost all the light that falls on them is absorbed into the material. Little or no light is reflected back toward our eyes, therefore we see ...
4
votes
2answers
153 views
Is it possible to charge photons
For example there are anti-particles to every particle we know,
Similary in some sense, is there a possibility that we can charge photons..if not what are the reasons and has there been any attempt ...
5
votes
3answers
211 views
Why the red-shift of distant galaxies is considered to be the effect of expanding spacetime?
Why it's not explained just by Doppler redshift caused by faster movement of those galaxies billions of years ago when that light was emitted?
Would the speeds of the galaxies necessary for Doppler ...
0
votes
1answer
112 views
Width of Gaussian Beam and Refractive Index
I know that in free space, the width of a Gaussian beam can be written as $W=W_0\sqrt{1+(\frac{z}{z_0})^{2}}$. However, I was wondering if it was possible to express this width as a function of ...
0
votes
1answer
158 views
Transmission of Gaussian Beam Through Graded-Index Slab
The $ABCD$ matrix of a glass graded-index slab with refractive index $n(y)=n_0(1-\frac{1}{2}\alpha^{2}y^{2})$ and length $d$ is $A=\cos(\alpha d)$, $B=\frac{1}{\alpha}\sin(\alpha d)$, $C=-\alpha ...
1
vote
0answers
121 views
Help With Difficult Deductive Proof [closed]
Suppose we have a Gaussian beam with a complex envelope expressed by the following equation 1:
$$\tag{1}
A_G(x,y,z) = \frac{A_1}{q(z)} e^{-ik \frac{x^2 + y^2}{2q(z)}}
$$
where
$$
q(z) = z+iz_0
$$
...
1
vote
2answers
114 views
Why energy saving light bulbs contain rare earth?
Reading a french article talking about a recycling unit of rare earth from energy saving light bulbs near Lyon - France (here is the official press release of the Salvay company), I was wondering :
...
0
votes
2answers
70 views
Is an electric lamp a transducer? [closed]
Silly thought.
A transducer, by definition, is a device that converts variations in one form of energy to another. An electric lamp converts electricity into visible light - the brightness may vary ...
2
votes
1answer
180 views
Different colors in LED/LCD display when viewed from different angle?
I want to know why different colours appear when viewed with a different angle. Can anyone tell me why?
0
votes
0answers
65 views
What about the photons that make you see ? [duplicate]
Possible Duplicate:
What determines color — wavelength or frequency?
Explanation about black color, and hence color
I understand that what we see are the reflected light from other ...
1
vote
2answers
139 views
Pulsed Spherical Wave
Can somebody help show me how a pulsed spherical wave has a wavefunction of the form U(r,t) = (1/r)a(t-r/c), where a(t) is an arbitrary function, r is the radius of the spherical wave, t is time, and ...
0
votes
0answers
56 views
Does redshifting the display color temperature actually makes one less awake? [closed]
I read that the blueish light from a regular computer screen makes one awake since that blueish light is like sunrise and day. To prevent that, one should not use computer screens some time before ...
1
vote
2answers
1k views
Why can't light pass through walls but sound can?
when i sit in a room....i can hear voices coming from the adjacent room but the light in adjacent room does not enter my room i.e. sound waves travels through the wall but light waves can't.why?
0
votes
0answers
58 views
Refractive index outside a vacuum [closed]
Refractive index is defined as n = c/v where c is the speed of light in the vacuum and v is the velocity of the light in a given material. Therefore refractive index outside of vacuum can be any ...
6
votes
5answers
781 views
Why is Light invisible?
Why can't we see light? The thing which makes everything visible is itself invisible. Why is it so?
-1
votes
1answer
157 views
Are all effects that change color perception examples of redshift/blueshift?
As defined by Wikipedia:
In physics (especially astrophysics), redshift happens when light seen coming from an object that is moving away is proportionally increased in wavelength, or shifted to ...
0
votes
1answer
81 views
Light in the absence of colloids?
If Earth had no colloids (Don't take LIFE into account) or any kind of scattering medium (like atmosphere) that promote to Tyndall effect, how would we able to receive the sun's rays? In the other ...
