This is a very basic question in optics: why the mathematical language we use corresponds to what we actually see. There are (at least) two ways to think of a decomposition of a visible light. One way is experimental: when a beam of light passes through a glass prism it decomposes to many beams according to their color. These colors are perceived by human eyes. The second way is theoretical: the light is thought of as electromagnetic wave satisfying the Maxwell equaitons in vacuum. Then one uses the Fourier transform with respect to the time variable to decompose a given solution as a combintaion of solutions of the form $\vec E(\vec x)e^{i\omega t}$.  If I understand correctly it is claimed in all stadard textbooks in optics that the above two decompositions correspond to each other in the sense that the frequancy $\omega$ determines the color of the light. Why? How do we know that the color is determined by the frequency of light and not by some other parameter? I could not find any clear explanation of this  correspondence so far. A reference would be helpful.  Remark. There is a similarly sounding question  It is different from my question, and the answers there do not answer my question.
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What determines the color of light -- is it the wavelength of the light or the frequency?  (i.e. If you put light through a medium other than air, in order to keep its color the same, which one would you need to keep constant: the wavelength or the frequency?)
109075
The reflection of a small light (but with enough power) on our TV shows four emerging rays. The rays vary periodically in space and have a repeating pattern of the colors of the rainbow. The further the flame is from the TV the greater the distance between the periodic lights in the "rays". Sounds reasonable.  This is the picture of the effect:    No matter how far you put the candle, the angle between the two lines stays the same. The color green is very faint in the picture but was clearly visible on the TV screen. The distance between successive red/green spots was getting smaller if the distance between your eye and the screen was getting smaller. Sounds reasonable. No matter how the light was positioned relative to the TV, the same pattern emerged.   I added a close-up picture of the working TV on which you can see what form the light-emitting pixels have:    Notice that they are curved, or better said, consist out of two little rectangles with an angle between them that is, at first sight, the same as the angle between the light rays seen on the TV-screen. When I measured the angle of the rays on the TV-screen it was about the same as the angle between the "line"-pieces of the pixels (about 180-(2x16)=148 degrees). Maybe here lies the clue to the problem. What would be the pattern seen on the TV-screen if the pixels would be square, rectangular (with the length vertically), or round? Or formed and arranged like here:    Surely not a flattened X! But to stay close to the question, what if the angle between the rectangular pieces of the pixels would be 180 degrees (so they become one rectangular) and positioned like in the lower right part of the above image? Would the X-form be stretched into a horizontal line (let's suppose all pixels, when the TV is off, reflect light equally well for what follows), with the colors of the rainbow repeating? In this case, a diffraction pattern is produced because of the different wavelengths of the colors in the rainbow. That is quite clear. All the red pixels reflect in such a way a light-dark pattern is found in the horizontal (squeezed X) line on the non-powered TV when we shine a light on it.  The fourth and fifth pictures I made by using a white and red LED (which shows the periodic Nature most clearly, and even red concentric rings), and in the sixth picture, I added some information on how I made the picture.   The last picture shows (somewhat fuzzy) the rectangular pixels and their configuration on my lap-top screen. It is the same forms of dots and they have the same configurations as in the pixels shown down left of the picture with four different forms and configurations. When I shine a light on my non-powered lap-top screen, I can discover no X-forms. It could be that the pixels don't reflect light.  But the final question: Are the same angles found in the pixels, (the big angle between the two rectangles) as in the big angle of the X correlated? If so, how?          I added this close-up picture of my laptop screen:    It's not that good visible, but the pixels are rectangular shaped (in vertical position). They are much smaller than the pixels on my big TV-screen, which I almost can see with the naked eye (once you know the shape after taking the close-up picture, which can't be said of the pixels of my laptop's screen). The effect isn't visible on my (power off) laptop screen, maybe because of the smallness of the pixels. The effect is (as I said ) color-dependent (with a red beam of light only a red X-form, periodically bright and dark is seen) and orientation independent (no matter how I point the light beam the same X appears over and over again). Nevertheless, I don't know if the pixels on both screens are the same (though it appears so).
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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 effect begins at about 510nm (greenish-cyan), where people mix in no red.  From that point on, the higher the frequency of the light source, the more red they mix in.    This effect is reflected by the red curve of the , which has an additional bump in the area of blue light.  However, that curve does not match the actual spectral sensitivity of red cones.  So where does this additional perception of red at higher frequencies come from?
47140
In music, when two or more pitches are played together at the same time, they form a chord. If each pitch has a corresponding wave frequency (a pure, or fundamental, tone), the pitches played together make a , which is obtained by simple addition. This wave is no longer a pure sinusoidal wave.  For example, when you play a low note and a high note on a piano, the resulting sound has a wave that is the mathematical sum of the waves of each note. The same is true for light: when you shine a 500nm wavelength (green light) and a 700nm wavelength (red light) at the same spot on a white surface, the reflection will be a superposition waveform that is the sum of green and red.  My question is about our perception of these combinations. When we hear a chord on a piano, we’re able to discern the pitches that comprise that chord. We’re able to “pick out” that there are two (or three, etc) notes in the chord, and some of us who are musically inclined are even able to sing back each note, and even name it. It could be said that we’re able to decompose a Fourier Series of sound.  But it seems we cannot do this with light. When you shine green and red light together, the reflection appears to be yellow, a “pure hue” of 600nm, rather than an overlay of red and green. We can’t “pick out” the individual colors that were combined. Why is this?  Why can’t we see two hues of light in the same way we’re able to hear two pitches of sound? Is this a characteristic of human psychology? Animal physiology? Or is this due to a fundamental characteristic of electromagnetism?
26571
I'm a newbie with physics but I'm wondering how a ray of light can essentially be represented. I have always known that a ray of light proceeds in a straight line until it encounters another object (or material) that refracts/reflects it. But a light ray should be part of an electro-magnetic wave, is this correct? If it is so, it should obey to the  and this doesn't seem to me to describe a straight line ray.  I'm having problems visualizing how light is emitted and how it relates with the wave equation. Can someone with a clear understanding of the problem explain it to me in simple terms?
115726
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 make a lens big enough to resolve individual atoms), and is this a light phenomena or an intrinsic wave phenomena?
37820
I believe that white light is white because it contains every wavelength, as white by itself has no frequency by itself.  Can somebody explain why really bright pure red, green, or blue LEDs seem white to us and to cameras?  Also, can a bright light ever be pure(eg is it possible to emit a pure red/pure blue/pure green bright light only with wavelengths in the range of that light), or will the inherent brightness of a light force other wavelengths into the light?
63732
I am reading Berkeley Physics Course vol. 4 (Quantum Mechanics) , chapter 4 (photons). (1)  Section 46: book says: consider a typical photon emitted by  the source. It can be regarded as a a wave train of finite duration, spreading out in all directions in space and carrying a total energy $\hbar\omega$. If this is true, a photon emitted by a star which is few light years away, would have spread over a sphere of radius of few light years. Then it is not possible to &quot;detect&quot; that photon using a detector.  Then  why does the book say like this?  In section 47, the book gives same example of photon spreading over light years. But in this section, it says that how the people can use this as a paradox; and clarifies that paradox by saying that classical expression for &quot;energy density&quot; refers to a large number of photons, and not for single photon.  So does photon really spread in all directions?   (2)  In Section 38 book says: almost monochromatic photons can not be split into 2 photons of the same frequency which carry only a fraction of the energy of the original photon. While in section 48, it says (with reference to double-slit diffraction experiment) photon came through BOTH the slits.  Does a photon REALLY goes through both the slits? Doesn't it indicate that a single photon can be split into two photons of same frequency ?   Any help will be appreciated. Thanks
50432
How can it be explained using the laws of refraction that a light through optical centre of a lens passes undeviated?  If we assume the portion of the lens in the middle to be made of even number of alternately place up and down prisms, then it's clear,  but why can the number of prisms not be odd?
87891
I am able to understand how light can be modeled to have wave characteristics from Young's double slit experiment.  But I am unable to comprehend how we can understand light to have particle characteristics from the photoelectric experiment. How is it wave character not able to explain the phenomena observed in this experiment? And how is it that particle nature defeats the wave theory?
34141
If you go to any course about photography, you learn that all colors are made up of the colors red, green and blue (RGB). (If you mix red, green and blue light, you will get white light, or any other color according to how much of each light color you use.)  If you ask a physicist, he or she will tell you that the visible light is made up of all the colors in the rainbow. The water splits the white light and shows the rainbow with all the different colors it contains.  What is color, and what is it made of? Are all the colors in the rainbow really basic colors, and photographers have just experienced that you can reproduce all those colors with red, green and blue? What is the commonly accepted idea about colors?
123533
I was studying a  problem where optical light with a wavelength of 500&nbsp;nm travels through a gas with refractive index $n$.  If we look at the equations for wave motion and index of refraction  $$c=\lambda_0\nu\quad\text{(in vacuum)}$$  $$v = \lambda\nu\quad\text{(in medium)}$$  $$n = c/v$$  we see that, if the frequency is constant, the wavelength decreases in the medium compared to vacuum. Is this a consistent property at all frequencies and for all mediums with refractive index real and greater than 1?  Are there dielectrics which change the frequency (still for n > 1), and is there an example of that?
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Maybe an illegal question. Sorry.  Having read that a photon has both wave and a light characteristics it is natural for a novice like myself to wonder "what is the amplitude? "  Naturally I have looked on wiki and other sources and there are a number of answers some of which appear not so much to contradict one another of varying opinions of which is the most meaningful in physics.   I seem to get a higher number of physics sources saying the amplitude depends on how many photons you have and if you have one the question has no meaning.  Of course I have not idea if this is accurate or how one would even test this.   Maybe there are some physics teachers in the audience that can give me a layman's intuition with a little math tossed in.
13076
I'm confused, does the absorption and emission determine the color of something? Or does that only happen when something is emitting energy?  When light hits an object, the photons get absorbed, then emitted with a different wavelength right?
15832
My father was colorblind, and I always wondered if colors were a matter of physics or if different colors are just a human way of describing and differentiating our visual perception of the world?  For example, is the color blue by nature blue, or is it just what we see?
117899
I am currently trying to get my head around the input-output formalism.  In describing the input-output formalism  , Gardiner and Collett take ladder operators in the Heisenberg picture and apply the Fourier transform to define the input operator.   Specifically, they start with ladder operator $ b(\omega)$, for a mode of frequency $\omega$  which takes the value $b_0(\omega)$ at time $t_0$ and then define the input field $b_{in}(t)$ as (for $t_0 &lt;t$):  $$b_{in}(t) = \frac{1}{\sqrt{2 \pi}} \int_{-\infty}^\infty d\omega e^{-i\omega(t-t_0)}b_0(\omega) \, .$$  I am confused as to how to interpret this. What frequency does the mode now correspond to if frequency has been 'integrated out'? Also is the operator $b_0(\omega)$ not already in the time domain, since it is specified at $t_0$? Could we not write $b$ as a function of $t$ and $\omega$ eg. as $b(t, \omega) = b_0(\omega)$ for $t=0$?  I would appreciate if anyone could clear this up. I suppose my specific questions would be:   How do we interpret the Fourier transform of an operator? Why do we do this in the case of the input-output formalism? What does $b_{in}(t) $ correspond to physically? Any other hints/tips for thinking about this kind of problem.
2134
Yesterday I read that we can affect the path and the 'form' (particle or wave) of a photon after the fact ().  Part of what is puzzling me is the beam-splitter. Are the individual photons actually being split into two new photons of lesser energy?  This  implies that you cannot split a photon but it seems that beam splitters do exactly that.