I have been considering this problem:     Colour is characterized by which of following character of light?      a)Frequency      b)Amplitude      c)Wavelength      d)Velocity   Different websites claim different answers; some claim wavelength, some claim frequency. My textbook is an average Indian textbook and has wavelength as the answer. I searched in standard books but did not find the answer.  But, as the wavelength changes from one medium to another medium, frequency does not change, and colour also does not change, it seems confusing to decide between frequency and wavelength. I consulted a teacher as well, he said wavelength, with logic I did not understand, and as he seemed to be in a hurry I did not feel comfortable to prolong the conversation.  References:          // says frequency             //says wavelength but answer mentioned(in the lower section of webpage) is frequency.     //says wavelength               //says wavelength     //says frequency
6451
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?)
4715
This is about a step in a derivation of the expression for the relativistic Doppler effect.  Consider a source receding from an observer at a velocity $v$ along the line joining the two. Light is emitted at frequency $f_s$ and wavelength $\lambda_s$. The frequency $f_0$ and wavelength $\lambda_0$ received by the observer will be different.  Some textbooks now argue that the wavelength received by the observer is given by $\lambda_0=(c+u)T_0$, where $T_0$ is the time period of the wave in the observers frame. The argument given is that the successive "crests" will be an extra distance $uT_0$ apart due to movement of the source. Upon relativistically transforming the time period in the source frame to the observer frame, the correct result $f_0=f_s\sqrt{\frac{c-u}{c+u}}$ is obtained.  But the argument for the wavelength seems reminiscent of the classical Doppler effect for sound. Is it really applicable here through this argument? And is there a way to show the same result for $\lambda_0$ mathematically?
21290
Observation:  So, I know that all computer screens are able to project many different colors by varying how they display the RGB (Red, Green, Blue) pixels.  Question  What's the difference between say, yellow light (575 nm) from sunlight vs. the same yellow light that's displayed on the computer screen? Aren't they different? Is our brains mixing together the RGB lights together and its being interpreted as yellow light or is yellow light the same (575 nm) light that comes from sunlight actually hits our eyes?  Relationship between Fourier Series and light?  1) So I know that in Fourier Series, you have basis functions, sines and cosines that make up any other function depending on the coefficients that are in front of the sines and cosines terms.  2) I know that RGB colors on a screen are the "basis" for all the other colors that a computer screen makes up and the intensity of each of the RGB are like the "coefficients". So, am I making the correct relationship here?
68624
in classical physics frequency represents how many cycles in one unit time, but I do not know how we define a frequency for a particle? what does it mean for a particle to have a frequency, the book I read it from just says Energy is proportional to the frequency of the photon but where is frequency?
73517
My understanding of colour is that atoms in a particular object will absorb certain wavelengths of electromagnetic radiation, and the scattered wavelengths give the object its colour. The absorbed wavelengths contribute to lattice vibrations, increasing the kinetic energy and raising the objects temperature. Is this correct?  What is the sequence of events when a solution of particular atoms is sprayed through a Bunsen burner? I don't understand this. In this case is the colour seen a result of electrons moving up and then back down energy levels?
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In basic quantum mechanics courses, one describes the evolution of quantum mechanics chronologically. Interference experiments with particles showed that particles should have a wave character; on the other hand, the photo-electric effect showed that electromagnetic waves should have a particle character. So there's a particle-wave duality.  The course continues with postulating the Schrödinger equation, and solves the problems for the wave character of classical particles (e.g. with respect to harmonic oscillators to solve the UV-catastrophe in the description of blackbody radiation). On the other hand, one describes the photo-electric effect extensively with perturbation theory, as the electromagnetic wave acts as a periodical force on an electron. But the electromagnetic wave is still described with the Maxwell equations, and not by Schrödinger.  Suppose history went a little differently: the corpuscular character would still be the generally accepted behaviour of light (as Newton preferred), and one discovered the wave character of photons and electrons simultaneously by doing interference experiments. The laws of Maxwell, Gauss, Faraday and Ampère weren't discovered yet. Schrödinger comes up with his equation, and one describes the wave character of electrons as well as photons with this equation.   Would this equation give a exhaustive description of the electromagnetic (and vector like) behaviour of photons? In other words: is the Schrödinger theory, in some way, equivalent to the Maxwell theory for the description of photons? Or are the Maxwell equations some kind of limit for greater dimensions (like the Newton equations for mechanics)? What is the link between these two "wave character" descriptions of photons?
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This asked:   And also this:     The second question is contradictory; maximum frequency -> minimum wavelength.   I am asking the very opposite;    What is the minimum frequency and maximum wavelenght of electromagnetic radiation?   The lowest measured/defined seems to be 3 Hz;  Which means a wavelenght 1/3 of the speed of light; ~100 000 000 m.   But this can't be the physical limit for the wavelenght. Does such a physical limit for the wavelength exist? (Similar limit like the speed of light is for velocity).
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The electromagnetic spectrum is a continuum of wavelengths of light, and we have labels for some ranges of these and numerical measurements for many.  Question: Is the EM spectrum continuous such that between two given wavelengths (e.g. 200nm and 201nm) there is an infinite number of distincts wavelengths of light?  Or is there some cut-off of precision with which light might exist (e.g. can light only have wavelengths of whole number when measured in nanometers, etc.)?
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Why do different wavelength get impeded more or less when in different materials? Moving with the same speed, but a longer physical distance would imply that the fields oscillate less times in the material, but I don't know why a difference in the number of oscillations would impede the wave- I don't even know why things slow down in general. Why some electromagnetic wave would slow down just because it's entering other electromagnetic fields... It would seem to me that the only factor would be time taken to physically move some electron or something in the direction of the fields... But that seems to simple of an explanation to me.
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When light passes from one medium to another its velocity and wavelength change. Why doesn't frequency change in this phenomenon?
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I am drawing a blank when it comes to equation transformation. Wikipedia  for the spectral radiance of black body:   First as a function of frequency $\nu$: $$I(\nu, T) = \frac{2 h \nu^3}{c^2}\cdot\frac{1}{e^\frac{h \nu}{k T} - 1}$$ Then as a function of wavelength $\lambda$ : $$I&#39;(\lambda, T) = \frac{2hc^2}{\lambda^5}\cdot\frac{1}{e^\frac{h c}{\lambda k T}-1}$$   And I don't see how they get $\lambda^5$ term. I'm assuming that the transformation is just $\nu \rightarrow c/\lambda$, but that gives $$ \frac{2 h \nu^3}{c^2} \Rightarrow \frac{2 hc}{\lambda^3} \neq \frac{2hc^2}{\lambda^5} $$  Similar transformation happens at other parts in the article also. I'm obviously missing something, likely completely trivial.
117469
When light (composed of photons with different frequency and wavelength) falls on a material, some of it gets absorbed and some get reflected depending upon the color of the material on which it strikes. And the material reflects the light of its own color only, thereby absorbing all the other colored light. So, my questions are:  How would a photon with certain wavelength (say 400 nm) decide to get reflected after striking the material of red color?   What is the actual mechanism behind the reflection of various colored light by the material of different color?
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I, like everybody I suppose, have read the  why the colour of the sky is blue:     ... the two most common types of matter present in the atmosphere are   gaseous nitrogen and oxygen. These particles are most effective in   scattering the higher frequency and shorter wavelength portions of the   visible light spectrum. This scattering process involves the   absorption of a light wave by an atom followed by reemission of a   light wave in a variety of directions. The amount of multidirectional   scattering that occurs is dependent upon the frequency of the light.   ... So as white light.. from the sun passes through our atmosphere,   the high frequencies become scattered by atmospheric particles while   the lower frequencies are most likely to pass through the atmosphere   without a significant alteration in their direction. This scattering   of the higher frequencies of light illuminates the skies with light on   the BIV end of the visible spectrum. Compared to blue light, violet   light is most easily scattered by atmospheric particles. However, our   eyes are more sensitive to light with blue frequencies. Thus, we view   the skies as being blue in color.   and why sunsets are red:     ... the light that is not scattered is able to pass through our   atmosphere and reach our eyes in a rather non-interrupted path. The   lower frequencies of sunlight (ROY) tend to reach our eyes as we sight   directly at the sun during midday. While sunlight consists of the   entire range of frequencies of visible light, not all frequencies are   equally intense. In fact, sunlight tends to be most rich with yellow   light frequencies. For these reasons, the sun appears yellow during   midday due to the direct passage of dominant amounts of yellow   frequencies through our atmosphere and to our eyes.      The appearance of the sun changes with the time of day. While it may   be yellow during midday, it is often found to gradually turn color as   it approaches sunset. This can be explained by light scattering. As   the sun approaches the horizon line, sunlight must traverse a greater   distance through our atmosphere; this is demonstrated in the diagram   below. As the path that sunlight takes through our atmosphere   increases in length, ROYGBIV encounters more and more atmospheric   particles. This results in the scattering of greater and greater   amounts of yellow light. During sunset hours, the light passing   through our atmosphere to our eyes tends to be most concentrated with   red and orange frequencies of light. For this reason, the sunsets have   a reddish-orange hue. The effect of a red sunset becomes more   pronounced if the atmosphere contains more and more particles.   Can you explain why the colour of the sky passes from blue to orange/red skipping altogether the whole range of green frequencies?  I have only heard of the legendary 'green, emerald line/ flash'     that appears in particular circumstances     Green flashes are enhanced by mirage, which increase refraction... is more likely to be seen in stable, clear air,... One might expect to see a blue flash, since blue light is   refracted most of all, and ... is   therefore the very last to disappear below the horizon, but the blue   is preferentially scattered out of the line of sight, and the   remaining light ends up appearing green   but I have never seen it, nor do I know anybody who ever did.
111576
Helmholtz distinguished between  and  trichromatic color theories.   Additive theories concern optical combinations of colored light sources and are usually modelled on RGB while subtractive theories model pigment mixing and are usually modelled on RYB or CMY.  What is the physical basis of this distinction?
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My understanding was that all objects emit light of continuous spectrum when hot ( black body radiation) but then you see discreet wavelengths in spectra lines and I am confused. I know I am making a mistake somewhere but not able to point it
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I don't understand how frequencies are defined in images/photographs. As far as I understand it now, high frequencies are like sharp things in images, like edges or so, and low frequencies are kind of the opposite?  I also would like to understand the outcome of Discrete Fourier Transformations, like how to read them properly.   It would be cool if somebody could explain to me the following:   What are frequencies in pictures and how are they defined? How do you read the outcome of a Discrete Fourier Transformation?
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I do scientific research, and I noticed for a lot of plots, the different curves are represented with different styles, but they are all black.  For instance, one curve may be a solid line, one may be a dashed line, one may be a dotted line with triangular markers, etc.  However, this makes it hard for me to differentiate between the curves.  Color is much more effective for helping people distinguish between data (and I’m taking a data visualization class that has research to prove it).  So... can I do this in my research article?  I imagine most people are keeping their plots black and white because of printing restrictions on color, but at the same time they include colors in all kinds of other figures in their document.  Also, how many people actually read printed articles anymore?  For scientific work, I look all of it up online.  Are there good reasons for me to stick with this backwards black-and-white scheme?