Physics nerd judging interest on an idea

[FatCat0]

Hello folks. As the title suggests, I am a physics nerd and I have an idea I'd like to try out, but I would like to know that at least one person might maybe read it since it will require a bit of work.

The other day in my spare time I started thinking about some of the physical concepts behind light and lenses that are very important to photography (again, nerd), and it kinda turned into an afternoon of on-and-off working out how individual settings affect the image that reaches your camera's sensor. I found this interesting (nerd) and thought that maybe a bunch of photography buffs would find some similar interest as well. So I've been tossing around the idea of making a mini series, probably in the lounge here since I think it's the most appropriate board on potn, where I would write little arguments for why things work out as they do and how they are important to photography (I swear I was never stuffed into a locker in high school).

Now, granted, I'm a second year physics major, and I'm 18 years old, and I'll almost literally be pulling most of this out of my hind-quarters and backing it up with physical arguments and logic as best as I can see it, so I'm going to go ahead and guarantee that at least some of it is going to be slightly inaccurate, if not entirely wrong. Also, pretty much everything in this topic would be a very simplified version of what really goes on in your camera. As many of you know, your lenses use anywhere from 4-8 or more aspherical lens elements, whereas I will be using strictly spherical lenses and generally only one (possibly always only one, I don't know if I ever have to use more than that to get my point across...but maybe in focusing).

I'll write a larger disclaimer in the actual topic should I go through with this, but suffice to say I'll be open to arguments though I will probably defend my position unless someone gives me very good reason not too. Actually even the defending my position part would probably make the whole ordeal better anyway because that would force me to find other ways to explain myself.

Anyway, like I said I'm just gauging interest right now. If you think you would at least glance at such a topic, please say so =)

[Jon]

Maybe if we saw some of the topics you're considering? "How DoF works"? Something like that? I'd be interested in seeing some of these.

[bps]

Anyway, like I said I'm just gauging interest right now. If you think you would at least glance at such a topic, please say so =)

If you want to gauge the interest level, you have to let us know what the topic (or topics) would be.

Bryan

[xarqi]

Just as a wee tester of your powers of explication, maybe you could explain to me in a few sentences why light refracts at a boundary between substances where the speed of light differs; not what happens, but how/why it does.

How does a photon/wave with no physical structure know its angle of incidence?
How does it detect a change in refractive index?
How does it calculate its new angle?
Why is this dependent on wavelength/energy?
How does it change direction?
If its momentum changes when it changes direction, where does the difference go in order that the total momentum is conserved?

Once we have that sussed, we can move on to how lenses work. ;)

[tonylong]

Just as a wee tester of your powers of explication, maybe you could explain to me in a few sentences why light refracts at a boundary between substances where the speed of light differs; not what happens, but how/why it does.

How does a photon/wave with no physical structure know its angle of incidence?
How does it detect a change in refractive index?
How does it calculate its new angle?
Why is this dependent on wavelength/energy?
How does it change direction?
If its momentum changes when it changes direction, where does the difference go in order that the total momentum is conserved?

Once we have that sussed, we can move on to how lenses work. ;)

You're so goofy, confusing us with all this photon-shmoton stuff!

Let's get down to real stuff -- how does the Force work, and what's the difference between the Light side of the Force and the Dark side?

To the OP -- are you a practicing photographer? That is, do you have a working knowledge of how to use the optics to get a shot? Will you be able to take particle physics/light and optical theory and boil it all down to something that a layman can grasp and put to use?

It sounds like a challenge, and could be interesting if you can come up with concise topics that are well-presented. But when you say some stuff could likely be inaccurate if not downright wrong, are you talking aout how your knowledge of physics applies to practical photography, or what?

[rklepper]

I think you are going to make a wonderful physicist. :)


I'll almost literally be pulling most of this out of my hind-quarters and backing it up with physical arguments and logic as best as I can see it, so I'm going to go ahead and guarantee that at least some of it is going to be slightly inaccurate, if not entirely wrong.

[FatCat0]

Hey, sorry I had to head to work.

I'm a little hesitant to post a list of topics should I not get to some, but eh why not. Here's what I have so far:
Zoom (hey, it'll be short but sweet)
Aperture
DoF
Focus (this is technically heavily involved in DoF so this will probably covered first)
Polarizers
Mayyyyyybe Bokeh, but I have to figure that one out first. I'm more looking to at least...propose a reason as to why different bladed apertures have different looking bokeh.

Uhh...I feel like I had more. I have stuff written down somewhere, but that's all I can remember off the top of my head.

I picked up photography as a hobby toward the beginning of the summer (which led me to this forum), so I am practicing, but my original intention was not specifically to improve your photography skills. I'm just looking to make people think a little, and hopefully someone finds it at least slightly interesting. If you do become a better photographer for it, kudos to you, but I wouldn't consider myself qualified to write something and guarantee it will help you out in practice. I do intend on making it understandable to everyone though, as long as you're willing to accept at least a little of what I'm saying on faith.

As far as applying this to photography, again I would take a very basic approach so applying what I'm writing EXACTLY to your camera wouldn't work. And as far as inaccuracy, I'm saying that again I'm pulling this all out of my understanding of things. One thing a professor of mine pointed out is that as a physicist you're constantly lied to throughout your education. You're told things work like this because of this. Then next year you learn well, they don't really always work quite like this, and it's because of this. Then the next year you learn that that other thing doesn't work in this case and this case. Unless it's a Tuesday, and in THAT case....

I'll get to you next post Xarqi

[FatCat0]

I think it'll be easier if I give a little conversation on light to explain most of your questions xarqi, but I'll take these two aside:
How does it change direction?
I couldn't tell you exactly how. Just that it does. Because it's light and it can do things like that.
If its momentum changes when it changes direction, where does the difference go in order that the total momentum is conserved?
I'll admit I can't give you an accurate answer for this one, especially off the top of my head. I'll think on it. I would be willing to bet that the fact that photons have zero rest mass comes into play, but that doesn't mean I would win the bet.

Now, the light conversation:
There is a concept, that I wouldn't vilify you for not having heard of, called optical path length. This is defined as OPL = nd, where n is the refractive index of the medium the light is in, and d is the physical distance that it travels. For rudimentary understanding purposes, it's okay to think of OPL as travel time. I'll explain a bit more on this later, but the higher the refractive index (n) of a medium is, the slower light moves through it. Light moving one meter through a vacuum may have an OPL of 1, while light moving one meter through something with an "n" of two would have an OPL of 2. The second path would take twice as long for light to traverse (vs the first path), thus the OPL is twice as large.

Light, when traveling from point A to point B, will travel along the shortest OPL (this is one of those things you're gonna have to take my word on, unless you REALLY want to know more but I feel that I would have to brush up on my theory a bit before I would be comfortable explaining this particular subject; it's harder to BS this than most of the photography stuff because I can't just draw a bunch of ray diagrams and hope for the best). Knowing this formula and this behavior of light you can actually derive the formula for refraction, which is n(1) * sin(theta(1)) = n(2) * sin(theta(2)), where the numbers after the n's distinguish your two mediums (first and second) and the ones after the theta's distinguish your two angles (before and after).

Now, the reason that the angle change makes sense...hey, it's time for a ridiculous analogy! Imagine you're walking diagonally toward a river at an angle of 20 degrees (measured from the side of the river). Upon stepping into the river you realize it's made of molasses. And filled with piranhas. Hungry little buggers at that. Also the molasses is on fire. Do you think you would continue your 20 degree angle trek and pass through a, say, 30 foot long fiery-molassesy-piranha-y experience, or would you change your angle slightly to say...90 degrees and just get the hell out as quickly as possible? Oh, and we're assuming you, much like light, are not a masochist.

To get back to being less ridiculous and more sciency, basically the light doesn't want to wade through the slower medium any longer than it has to. Something else you should know is the formula for n, the index of refraction of a substance that light is passing through. n is defined as n = c/v, where c is the speed of light in a vacuum and v is the speed of light in the substance. So n(vacuum) = 1, and any other substance has a value greater than 1 since, due to some very complicated reasons, light moves slower when there's stuff in its way (I actually just lied to you a bit there; I've heard of man-made substances with negative refractive indices, so technically the absolute value has to be greater than 1, but it's not a huge point. Also I know virtually nothing about HOW these things work, so I'd like to avoid the subject as best as I can). So when a medium has a higher refractive index, the light moves through it slower, and thus takes a shorter path through it so its overall journey is as fast as possible.

As to how a photon knows its Angle of Incidence, well...it's a wave, so it acts like one. That's just about the best answer I can give for that.

Why is this dependent on wavelength/energy? Well, I'd like to point out first that wavelength and energy are connected. That is, E = hf (energy = h (a constant) * frequency), and f = c/lambda (frequency = speed-of-light/wavelength), so E = (h*c) / (lambda) (energy = h * c / wavelength). That's actually irrelevant to a basic reason as to why it's dependent, but I think it's worth pointing out. The reason for why different wavelengths of light refract differently is because many mediums have varying refractive indices for the different wavelengths of light. If you look back to the equation n(1) * sin(theta(1)) = n(2) * sin(theta(2)), you can see that if you keep your n(1) (assume you're moving through air at first) and theta(1) (and at a constant angle) the same, and change your n(2) (the index of the medium you'll be moving through, say a prism), your theta(2) will have to change.

This is a fairly complex subject, and I composed most of this amidst talking to my mom and watching "1000 Ways to Die" on TV. Sorry I went over the few sentences guideline, and also sorry I rambled a bit and did a poor job of really simplifying things, but I assumed if you're asking questions like these you have at least enough of a grasp of the subject that you should be okay with what I wrote. If you need anything clarified, do point it out. And I would like to point out that my photography discussions will be more well organized and descriptive (with diagrams!).

I suppose I could give a summary answer to your first question:
Light refracts (that is, changes the angle at which is is traveling (measured from the boundary you are crossing)) because it wants to traverse the shortest optical path length it can. The reason it does this is because it is light and it can. Again because it is light. That's pretty much the best I can give you without rambling.

[FatCat0]

Oh, and I think there are more than enough people (i.e. more than 0) interested in popping in and reading my madness for me to have an excuse to do this, so I'm not going to make any promises as to when this topic will show up but it shall.

[Jim G]

I'd be interested in taking a look. Always curious to see what's going on behind the scenes, so to speak.

[xarqi]

Now do realise that I am being a little ornery deliberately here, so as to help you hone your skills to help me understand, as it were. If I get out of line, let me know and I'll back off.

OK.

How does it change direction?
I couldn't tell you exactly how. Just that it does. Because it's light and it can do things like that.

Unfortunately, that is the crucial question. Without understanding that, refraction and dispersion just have to be taken as axioms.


If its momentum changes when it changes direction, where does the difference go in order that the total momentum is conserved?

Oh light has momentum all right: e = mc^2 and all that. I wouldn't be at all surprised if (gasp) its wavelength changed on the way across the boundary, and if some energy was imparted to the medium (shock). Rayleigh scattering rings a bell here, and something about light sails and red shifts and the size of the universe.

As for OPL, etc, well, the question becomes why does light follow a geodesic? It's probably a "path of least resistance thing, but I wouldn't be at all surprised if it actually takes all paths simultaneously with different probabilities, and we just observe the average, usually that is.

Nah - I don't buy the treacle analogy, sorry. Under that scheme, the angle of refraction would always be normal to the boundary. I also don't buy the more usual "trolley hits a patch of wet tar at an angle" one either as photons have zero size (hint: or do they?) and photons in a beam aren't connected in the way trolley wheels are.

So when a medium has a higher refractive index, the light moves through it slower, and thus takes a shorter path through it so its overall journey is as fast as possible.
But it doesn't - that's the treacle fallacy again. It takes a faster route, sure, but not the fastest.

Your explanation of the wavelength dependency is circular. There is an equation that describes what has been observed, and when we plug numbers into it, lo and behold we can make predictions. That doesn't answer the "why" question at all.

Light refracts (that is, changes the angle at which is is traveling (measured from the boundary you are crossing)) because it wants to traverse the shortest optical path length it can. The reason it does this is because it is light and it can. Again because it is light. That's pretty much the best I can give you without rambling.
I like a good nature ramble!

[Rudeofus]

How does a photon/wave with no physical structure know its angle of incidence?

How does it calculate its new angle?

It doesn't. It's their collective distribution which changes. A commonly used method to calculate their probability distribution of photons is by solving the maxwell equations. The maxwell equations tell you that refraction will occur but nothing about the individual photon.

How does it detect a change in refractive index?

Through interaction with the new media.

Why is this dependent on wavelength/energy?

Because material interacts differently with photons depending on their energy/impulse. It's called dispersion. That's why color filters exist and many other useful effects.

How does it change direction?
If its momentum changes when it changes direction, where does the difference go in order that the total momentum is conserved?
Which momentum (http://letterstonature.wordpress.com/2007/01/05/refraction-its-so-hot-right-now/) are you talking about anyway? :lol:

[tonylong]

How about this for an analogy of a large quantity of photons which define a "beam" can change direction:

If I take a large amount of water, composed of countless numbers of molecules, and pour it into a system of water, many, many individual molecules will be dispersed. But, if there is to be found a "path of least resistance" that at the same time allows the forward (downhill) momentum of the water to continue, the main body of water will naturally be funneled to that path because of a combination of resitance factors will keep all the water from being equally dispersed in random directions and the result will be what we call a stream of water or a beam of light that will be defined not by the behavior of an individual molecule or photon (many of which will be dispersed) but by a body of molecules/photons which are "funneled" into that fastest flow -- not a straight line but still the path that combines less resistance and conforming to the forward momentum.

There's my common-sense take on it!

[xarqi]

Thanks for contributing Rudeofus. So - in my "troublesome student" role:

It doesn't. It's their collective distribution which changes. A commonly used method to calculate their probability distribution of photons is by solving the maxwell equations. The maxwell equations tell you that refraction will occur but nothing about the individual photon.
A "stop" sign tells drivers to stop, and allows me to predict that this is what I will normally observe, but it doesn't explain the mechanism for doing so. Maxwell's equations, and dare I say all such similar equations, are descriptive, not mechanistic. Citing Maxwell is no more satisfactory than citing Snell.

Through interaction with the new media.

The thrust of my comment was that it must somehow be aware of this before entering the medium in order to know at what angle to do so. We seem to be at the point now where we can accept that something happens to a wave/photon as it hits a boundary obliquely that causes it to change direction. What?


Because material interacts differently with photons depending on their energy/impulse. It's called dispersion. That's why color filters exist and many other useful effects.
To restate my question then, why is the speed of light in a dispersive medium dependent on wavelength? Not just because the equations say it must be, surely. What is the physical interaction that occurs between light and matter that is energy/wavelength dependent? Or do we simply not know and accept it as axiomatic?

Which momentum (http://letterstonature.wordpress.com/2007/01/05/refraction-its-so-hot-right-now/) are you talking about anyway? :lol:
Interesting read. In either case though, if energy is imparted to the medium in order to conserve momentum, then the wavelength of the light must change on refraction as it gives up energy! This must complicate things a bit as the degree of refraction determines the change in momentum, the change in momentum alters the wavelength, and the wavelength determines the degree of refraction. (Somebody call Zeno, quick!)

[Karl Johnston]

I think you'll make a great physicist...reason being, I lost you after this paragraph

The other day in my spare time I started thinking about some of the physical concepts behind light and lenses that are very important to photography (again, nerd), and it kinda turned into an afternoon of on-and-off working out how individual settings affect the image that reaches your camera's sensor. I found this interesting (nerd) and thought that maybe a bunch of photography buffs would find some similar interest as well. So I've been tossing around the idea of making a mini series, probably in the lounge here since I think it's the most appropriate board on potn, where I would write little arguments for why things work out as they do and how they are important to photography (I swear I was never stuffed into a locker in high school).

[sheawyatt]

I'm so glad I'm a biology student. You physicists sure are a special group of people...(I mean that in the best way possible).

[FatCat0]

Ewww, biology =P

I kid of course. I find lots of biology fascinating and love learning about it, but there's far far too much memorization for my tastes.

[FatCat0]

Oh, and xarqi I'll attempt to make a rebuttal tomorrow or Wednesday, I'm tired tonight. I'll just touch on this real quick.
Now do realise that I am being a little ornery deliberately here, so as to help you hone your skills to help me understand, as it were. If I get out of line, let me know and I'll back off.As long as you don't cross the line into abusive, be as ornery as you like =) Being challenged is one of the best ways to learn. Just remember, no promises that I'm actually capable of answering your questions adequately.

[Daniel Browning]

I'm so glad I'm a biology student. You physicists sure are a special group of people...(I mean that in the best way possible).

http://imgs.xkcd.com/comics/purity.png

[Karl Johnston]

http://farm4.static.flickr.com/3251/3765155544_eb60254ab8_o.jpg

[sheawyatt]

http://farm4.static.flickr.com/3251/3765155544_eb60254ab8_o.jpg

Please tell me that is a camera he's holding...

I love xkcd, and agree with that comic 100%. And this one:

http://imgs.xkcd.com/comics/cuttlefish.png

[Karl Johnston]

Of course, what else would it be? It's clearly an L lens :P see the red ring?

[Rudeofus]

A "stop" sign tells drivers to stop, and allows me to predict that this is what I will normally observe, but it doesn't explain the mechanism for doing so. Maxwell's equations, and dare I say all such similar equations, are descriptive, not mechanistic. Citing Maxwell is no more satisfactory than citing Snell.

Note that the current justification for all these theories owes entirely to the fact that they describe observed results well. To this day nobody knows why the Schrödinger equations really hold, same thing applies to the equations governing relativity and most other physics theory derived from these (which includes the Maxwell equations). Demanding clarification of these issues basically ends the whole discussion right here.

The thrust of my comment was that it must somehow be aware of this before entering the medium in order to know at what angle to do so. We seem to be at the point now where we can accept that something happens to a wave/photon as it hits a boundary obliquely that causes it to change direction. What?

Now you get entangled in quantum physics. Note that there is no exact location of photons and no exact time, when they cross a boundary. You must not treat photons as tennis balls or you run into big trouble when you deal with interference phenomena.

To restate my question then, why is the speed of light in a dispersive medium dependent on wavelength? Not just because the equations say it must be, surely. What is the physical interaction that occurs between light and matter that is energy/wavelength dependent? Or do we simply not know and accept it as axiomatic?

If photons interact with material, they do so via interaction with electrons. A nice example of this is white light going through gas clouds (where certain spectral lines get absorbed, that's used in astronomy a lot). Think of it like this: the reason materials have n>1 is because they somehow interact with photons, so it's reasonable to assume that there is a dependency on photon energy in that. Another nice procedure where the energy dependency of photon interaction is used is laser cooling. Oh, and color filters, I almost forgot these :lol:

Interesting read. In either case though, if energy is imparted to the medium in order to conserve momentum, then the wavelength of the light must change on refraction as it gives up energy!

The paper proposes energy transfer (changing water levels) from the forces applied to the interface. However, the simple laws of refraction assume that the boundary is held in place so no energy is tranferred. Read here (http://arxiv.org/pdf/physics/0510263) for a paper where the Snellius laws of refraction are deducted from conservation of energy and momentum (and some trivial quantum physics considerations).

This must complicate things a bit as the degree of refraction determines the change in momentum, the change in momentum alters the wavelength, and the wavelength determines the degree of refraction. (Somebody call Zeno, quick!)
Since no energy is transferred, the frequency of the photons stays the same. Hence the wavelength remains only depending on the respective medium the photon travels in.

Note, that the concept of medium is only an approximation once you reach quantum distances, since the photon interacts with atoms/electrons, not with a continuum. So a photon doesn't know whether it's in a medium or not. It interacts with other particles around it in ways described by quantum physics, and if certain particles interact with it, it's wave length changes (what's a wavelength of a particle anyway???).

[Darsk47]

Slightly off topic - more in line with the comics posted above, but a link to some physics/math test answers :

http://www.uoregon.edu/~gilkey/dirhumor/ExamQuestions/ExamQuestions.html

( I find this thread quite interesting btw)

[Jon]

Slightly off topic - more in line with the comics posted above, but a link to some physics/math test answers :

http://www.uoregon.edu/~gilkey/dirhumor/ExamQuestions/ExamQuestions.html

( I find this thread quite interesting btw)Notice where his office is? :{)#

[tonylong]

Notice where his office is? :{)#

Are you referring to Oregon? Heh! I'm on the other side of the river, so no aspersions shall stick to me:)!

[xarqi]

Good stuff, Rudeofus. Food for thought.

Now, FatCat0, your turn.

[Jon]

Are you referring to Oregon? Heh! I'm on the other side of the river, so no aspersions shall stick to me:)!
Not that. Go back and read the fine print . . .

[rklepper]

So where would you put a Biophysical Chemist?


http://imgs.xkcd.com/comics/purity.png

[CyberDyneSystems]

Diffraction?

It's all parallel universes! Surely!

Everett.

[zaathrus]

Heh, good to see some familiar stuff (and proof that I didn't sleep through ALL my lectures!) Also good to note that we still do not understand everything about photons or light and that much of what we think we understand may be disproved tomorrow...

So do photons interact with electrons only in boundary transitions? Or is there more to it than that I wonder?

Why am I now haunted by the memory of 4D integrations and quantum mechanics? Can I go home now?

And as for the Chemist vs Physicist vs Mathematician argument - at least Chemists & Physicists are useful... (And everyone knows that Chemistry is a superior discipline as it knows and admits that theory = practice except in the real world. Fugacity coefficients FTW!)

[Rudeofus]

So do photons interact with electrons only in boundary transitions? Or is there more to it than that I wonder?

They do it all the time. Most of the time to such an extent that most solid materials won't even let them through. I guess we've talked so much about glass here that nobody thinks of all the intransparent materials out there :lol:

[20droger]

They do it all the time. Most of the time to such an extent that most solid materials won't even let them through. I guess we've talked so much about glass here that nobody thinks of all the intransparent materials out there :lol:
It's almost all transparent. It just depends upon the energy of the photons in question. Shake 'em hard enough and fast enough and they go through lead.

And there's no such thing as gravity. The Earth sucks!

[FatCat0]

It's almost all transparent. It just depends upon the energy of the photons in question. Shake 'em hard enough and fast enough and they go through lead.

And there's no such thing as gravity. The Earth sucks!

Funny story, I got in trouble in high school for wearing a "Black holes suck" t-shirt.

And yes I know it's long past my turn, but 19 hour work days also suck. Mostly time and energy. And I'm headed out to work again. Sorry I kinda fell by the wayside of the conversation, I promise to jump back in soon.

[20droger]

Funny story, I got in trouble in high school for wearing a "Black holes suck" t-shirt.

And yes I know it's long past my turn, but 19 hour work days also suck. Mostly time and energy. And I'm headed out to work again. Sorry I kinda fell by the wayside of the conversation, I promise to jump back in soon.
Tell your boss about this new discovery, called "sleep"!

And if you're the boss, you have my sympathy. Been there. Done that.

[FatCat0]

Again I find myself low on time, so I can't go back and get through the whole topic, but I do want to point out a couple things from one of your earlier posts:

Nah - I don't buy the treacle analogy, sorry. Under that scheme, the angle of refraction would always be normal to the boundary. I also don't buy the more usual "trolley hits a patch of wet tar at an angle" one either as photons have zero size (hint: or do they?) and photons in a beam aren't connected in the way trolley wheels are.
First, it was a loose analogy and if I remember correctly I did make a statement that I shouldn't have, namely something about cutting to an angle close to 90 degrees as this does imply something about refraction angles wanting to be 90 degrees. In my analogy I should've pointed out that the medium we were traveling through had a refractive index close to infinity.

I have an argument against this point, but not the time to write it out (partially due to the fact that I already tried to simplify it too much and realized I lost my point in doing so, but not after wasting roughly three quarters of an hour writing it out amidst eating and other things). Another day.



But it doesn't - that's the treacle fallacy again. It takes a faster route, sure, but not the fastest.

Your explanation of the wavelength dependency is circular. There is an equation that describes what has been observed, and when we plug numbers into it, lo and behold we can make predictions. That doesn't answer the "why" question at all.

I didn't really attempt to explain wavelength at all really, just kinda pointed out THAT there's a dependency. If you want something simple to chew on, take my word for it that frequency doesn't change when the medium changes. Since you're moving in a medium with a different speed than you started out with (v < c), and the same frequency, since v = f*lambda (velocity = frequency * wavelength), if v changes then lambda has to change proportionally. Now, I'm asking you to make a big assumption on the frequency thing, but as far as just pointing at a formula and saying "Look, it works", in this case the formula is mechanistic itself. It's simple, velocity is a function of distance/time. Frequency is a function of /time, and wavelength is a function of distance. So you end up with a distance per time, which literally *is* velocity.

Also more related to the original post of this topic, I've started making my building blocks for my diagrams in photoshop, so hopefully despite my total lack of art skill I should at least be able to demonstrate my point. I'm going to start with a quick lesson on ray tracing (if you don't know what it is, you will soon!) because I'm going to use that throughout the whole series. Once I get the necessary bits made I'll slap something together quick and get lesson 1 out there. The discussion bit is all but done in my head, the diagrams just take some time. Again, noooooo artistic ability. I'm even using a tablet PC. It's just reinforcing that lack of ability since nothing is coming out remotely symmetrical. It should be up by the end of the week, I hope.

[xarqi]

I didn't really attempt to explain wavelength at all really, just kinda pointed out THAT there's a dependency.
True, but why is there a dependency?

If you want something simple to chew on, take my word for it that frequency doesn't change when the medium changes.
I can accept that.

Since you're moving in a medium with a different speed than you started out with (v < c), and the same frequency, since v = f*lambda (velocity = frequency * wavelength), if v changes then lambda has to change proportionally.
No problem at all. Wavelength changes. Gee - does that mean that colour changes, with red photons turning bluer?
Now, I'm asking you to make a big assumption on the frequency thing, but as far as just pointing at a formula and saying "Look, it works", in this case the formula is mechanistic itself. It's simple, velocity is a function of distance/time. Frequency is a function of /time, and wavelength is a function of distance. So you end up with a distance per time, which literally *is* velocity.
None of which sheds any light at all on why the angle of refraction should depend on the wavelength.

[Rudeofus]

I didn't really attempt to explain wavelength at all really, just kinda pointed out THAT there's a dependency.
True, but why is there a dependency?

Covered here (http://photography-on-the.net/forum/showpost.php?p=8356697&postcount=23).

If you want something simple to chew on, take my word for it that frequency doesn't change when the medium changes.

I can accept that.

That follows from conservation of energy. Photon energy is h*f with h being the planck constant and f the frequency. Since no energy is transferred anywhere, f must stay constant.

Wavelength changes. Gee - does that mean that colour changes, with red photons turning bluer?
1. Before the light hits your eye, it has to leave the medium, at least I hope so :p
2. The chemical reactions triggered on your retina depend on photon energy, not impulse, hence are not directly linked to their wave length.

None of which sheds any light at all on why the angle of refraction should depend on the wavelength.
As mentioned: the dielectric properties of a medium come from interactions of the medium with the photons. The interactions between medium and photons depend on photon energy, hence frequency, hence wave length.

[rklepper]

BUT, photon energy is inversely proportional to the wavelength.


2. The chemical reactions triggered on your retina depend on photon energy, not impulse, hence are not directly linked to their wave length.

[Rudeofus]

BUT, photon energy is inversely proportional to the wavelength.
That's only correct as long as you stay in the same medium. The equation E = h*f holds in any medium and across media.