1. I saw a beautiful rainbow over the river the other day. I stopped and stared at it. I realised that I dont understand what I am seeing when I observe a rainbow.

It would be good to see how deep an understanding we can get together here on the science forum, of rainbows.

Sometimes a rainbow can seem to be about 10/20 metres from one side to another, each colour in the spectrum is maybe 1 metre or more wide. Millions of water particals all appear the colour of the band they appear in.

It's not a case of each water partical refracting every part of the spectrum... it's a case of them all doing it collectively. How does this work? What exactly are we seeing?

Can anybody explain whats going on with rainbows in any detail?

2.

3. Does it ever occur to you to look it up?

Rainbow - Wikipedia, the free encyclopedia

4. Yep that was my plan... I ask a question then look up the answers!

Are you suggesting I am misusing the forum in some way?

5. No, simply that you weren't making the maximum use of the resources you have at hand.

6. It occurs to me that the answers I seek are not on wikipedia.

I wish to know why if a rainbow is light refracting inside a water droplet, why isnt each water droplet multi coloured? why are is there an arch of seperate water droplets that reflect one colour, then another arch of another colour and so on?

Also... why is it that these colours become visible through refraction?

I need somebody with some understanding to have a discussion with.

7. Hi qfy, I think this is a rather apt post for me to respond to as I saw an absolutely superb rainbow over Norwich, spent all afternoon christmas shopping and got absolutely drenched. But as the rain began to die down and the sun returned we were greeted with the most amazing rainbow which was quite inspiring. But basically a rainbow is like millions of tiny prisms hanging in the sky splitting the suns rays into the visible colours that we can see. Since the light all comes through all the rain drops at the same angle (42 degrees according to the wiki page, which I didn't actually know the angle till I just read read it) they appear to line up like one big curved prism but in reality it's more like shining a light at angle through a piece of mesh. The light will look like one big mass, but is only coming through certain closely spaced holes at the same angle. This happens to work the same way no matter where you are positioned, with the light always being broken into the rainbows colours at this same angle it means the colours remain constant and in the same place, the amount of water molecules just helps to determine how strong the colours appear.

8. I wish to know why if a rainbow is light refracting inside a water droplet, why isnt each water droplet multi coloured?
It is. The color you see depends on the angle you view the water droplet from.

why are is there an arch of seperate water droplets that reflect one colour, then another arch of another colour and so on?
Each arch you see is generated by the angle between you and the water droplets.

It occurs to me that the answers I seek are not on wikipedia.
Wiki's got the answers to everything you've asked (so far). I would suggest that you look it up first, and then, equipped with some knowledge, you start a discussion.

9. Originally Posted by AlexG
I wish to know why if a rainbow is light refracting inside a water droplet, why isnt each water droplet multi coloured?
It is. The color you see depends on the angle you view the water droplet from.
Ok I understand.

Why would that be the case? Why do certain frequencies reflect at slightly different angles?

[QUOTE=AlexG;371559]
It occurs to me that the answers I seek are not on wikipedia.

Wiki's got the answers to everything you've asked (so far). I would suggest that you look it up first, and then, equipped with some knowledge, you start a discussion.
I read it. But I find it easier to get somebody into a conversation.

Why do only certain frequencies get reflected into our eyes at certain angles?

What does this tell us about light? are frequencies of light mingled everywhere or is there a structure to the way light frequencies 'radiate'?

Why do certain frequencies reflect as a certain colour?

10. Originally Posted by question for you
Why do only certain frequencies get reflected into our eyes at certain angles?

What does this tell us about light? are frequencies of light mingled everywhere or is there a structure to the way light frequencies 'radiate'?
Newton? Prism? Spectrum? No, nothing?

What do they teach these people at school nowadays...

(I'll let someone else explain; I have to eat something)

11. Originally Posted by Strange
Originally Posted by question for you
Why do only certain frequencies get reflected into our eyes at certain angles?

What does this tell us about light? are frequencies of light mingled everywhere or is there a structure to the way light frequencies 'radiate'?
Newton? Prism? Spectrum? No, nothing?

What do they teach these people at school nowadays...

(I'll let someone else explain; I have to eat something)
Well i'm sorry that this is all so mundane for you all.

Newton, measurement of force named after a phycicist who did a lot of work with force. Prism: Shape that refracts the colours of the rainbow. Spectrum: Various frequencies of light.

In all honesty odd one, I don't think you comprehend the question, let alone the answer.

12. Originally Posted by question for you
In all honesty odd one, I don't think you comprehend the question, let alone the answer.
Of course he knows. He went to school and paid attention. And he reads a lot.

A prism works by bending different colors by different angles (if the angles weren't different, you wouldn't see white light resolved into its separate colors). The raindrops are little prisms.

Search terms for your further study: Refraction; dispersion; spectrum

13. Come on guys lets not knock someone for wanting to discuss something and learn, we all have some gaps in our knowlegde, save the knocks for people you've told something a 100 times and don't want or are unwilling to learn!

14. I don't mean to be rude QfY but it is tricky to know how basic to go with you sometimes.

Are you aware that when we perceive colour it is due to different wavelengths (or equivalently, frequencies) hitting the retina? (The retina is part of the eye, you know. )

What we see as white light (e.g. sunlight, which is approximately white) is a mixture of different frequencies. The combination of all of these is interpreted by our brains as white.

When light passes through a material (glass, water, air, whatever) it slows down. The amount by which it slows down is called the refractive index. This causes the angle of a ray of light to change when it moves between one material and another. You can see this if you stick a straw in a glass of water: at certain angles, the straw will look bent.

In most transparent materials, the refractive index increases with increasing frequency. This means that different frequencies (colours) get bent by different amounts. This is why white light get split into a range of colours by a prism or a drop of water.

But then again, optics was the reason I failed my first year of university so ...

15. Originally Posted by tk421
Originally Posted by question for you
In all honesty odd one, I don't think you comprehend the question, let alone the answer.
Of course he knows. He went to school and paid attention. And he reads a lot.
That's no garentee that he gave my question much thought.

Originally Posted by tk421
A prism works by bending different colors by different angles (if the angles weren't different, you wouldn't see white light resolved into its separate colors). The raindrops are little prisms.
So the frequency of the wave has a direct affect on the angle of refraction? Which means that in a single prism like a water drop, the 360 x 360 surface of the prism will refract all the colours of light degrees apart so you could see a rainbow from a droplet.

But why do dropplets appear coloured on mass in rainbows instead of lots of tiny rainbows?

Does distance from the prism affect the width the spectrum appears? i.e the further the cloud, the bigger the rainbow?

16. Originally Posted by question for you
But why do dropplets appear coloured on mass in rainbows instead of lots of tiny rainbows?
Have you ever bounced a ball off the angle between the floor and a wall? It always bounces back towards you, whatever angle you throw it at.

17. Originally Posted by Strange
I don't mean to be rude QfY but it is tricky to know how basic to go with you sometimes.
Yes you do mean to be rude you blinking liar!

With technical terms you need to go slow, with fundamentals of science I can grasp things reasonably well I guess.

Originally Posted by Strange
Are you aware that when we perceive colour it is due to different wavelengths (or equivalently, frequencies) hitting the retina? (The retina is part of the eye, you know. )

What we see as white light (e.g. sunlight, which is approximately white) is a mixture of different frequencies. The combination of all of these is interpreted by our brains as white.
C'mon give it a rest, none of my questions are this basic surely?

I've heard the basics, I want a more technical understanding, it's just the terminology takes a while.

Originally Posted by Strange
When light passes through a material (glass, water, air, whatever) it slows down. The amount by which it slows down is called the refractive index. This causes the angle of a ray of light to change when it moves between one material and another. You can see this if you stick a straw in a glass of water: at certain angles, the straw will look bent.

In most transparent materials, the refractive index increases with increasing frequency. This means that different frequencies (colours) get bent by different amounts. This is why white light get split into a range of colours by a prism or a drop of water.

But then again, optics was the reason I failed my first year of university so ...
Hmm yes so indeed...

What has the amount a frequency of EM radiation slows down by got to do with the angle it reflects from a prism, or surface of a material?
In what way does it 'slow down'?

Also you touched on an interesting point about how we interpret a very small amount of the EM spectrum as the different types of visible light. Whats so special about the visible spectrum I wonder. What is it about us that interprets this part of the spectrum the way it does? And why not perceive other parts of the spectrum? Insects do. Don't tell me... it's because we didn't need it in our evolution.
What is actually happening, is it that our nuerons can only 'resonate' with this small part of the spectrum? do the EM frequencies of the rainbow correspond to the EM frequencies of the biological body or part of the brain resonsible for sight?

18. Originally Posted by Strange
Originally Posted by question for you
But why do dropplets appear coloured on mass in rainbows instead of lots of tiny rainbows?
Have you ever bounced a ball off the angle between the floor and a wall? It always bounces back towards you, whatever angle you throw it at.

A ball doesn't always bounce back to you from a floor/wall joint. If you were inside a sphere it would always come back to you.

This diagram doesn't explain how we see a thick band of violet, then indigo then aquamarine or whatever they are called up to red, in the sky in front of us.

A 7 metre thick rainbow in the sky is not projected from one single prism. How can all those rain drops act as a single prism producing clearly defined and thick bands of colour in the sky?

19. How much is the beam of light 'dispersed'? I mean in 3 or 4 dimensional units. How much 'thicker' does the beam become through refraction?

Do you know where the equation for that is?

20. Originally Posted by question for you
What has the amount a frequency of EM radiation slows down by got to do with the angle it reflects from a prism, or surface of a material?
When the light hits the boundary and slows down, it causes it to change direction:
Refraction-Water-Waves.gif
(That diagram uses the change in speed in water due to a change in depth, but it is the same thing.)

Note this is refraction, not reflection.

In what way does it 'slow down'?
The classical (light as wave) explanation is that the permeability and permittivity (two properties of a material) change which changes the speed of light in the material (like making a liquid thicker - as a poor analogy).

The more modern explanation involves quantum electrodynamics (QED) which I am not even going to attempt to explain (but there are some good videos on line of Feynman doing a series of non-technical lectures, which are worth watching).

Whats so special about the visible spectrum I wonder. What is it about us that interprets this part of the spectrum the way it does? And why not perceive other parts of the spectrum? Insects do. Don't tell me... it's because we didn't need it in our evolution.
Exactly. The same reason that the hole that a puddle sits in is exactly the same shape as the water.

What is actually happening, is it that our nuerons can only 'resonate' with this small part of the spectrum? do the EM frequencies of the rainbow correspond to the EM frequencies of the biological body or part of the brain resonsible for sight?
Kinda. There are proteins in the the eye which respond to different wavelengths of light (you can think of them as red, green and blue but they are more like yellowish, greenish and blue). When these absorb light they generate a signal which is sent to the brain. The brain then generates all the colours we see from this crude information.

Other animals are sensitive to different ranges of frequencies and some have more than three types of colour-sensitive receptor. (Depending on their evolutionary needs.)

21. so,
you sumed it up nicely
..
which raises a question that maybe you can answer
when CO2 molecules are excited by various light frequencies, they stretch, or bend, or twist based on the frequency of the spectrum.
assuming that water does the same(stretching mostly at the higher frequencies, and bending at the lower, does this effect the refractive index?

22. Originally Posted by sculptor
assuming that water does the same(stretching mostly at the higher frequencies, and bending at the lower, does this effect the refractive index?
Interesting question. I don't think so. The refractive index is caused by the interaction of photons with the electrons in the atoms. The bonds themselves probably affect this in some way by changing the energies of the electrons (I don't really know) but the bending/and stretching would, I'm pretty sure, be insignificant. Also, the bending and stretching absorption bands are in the infra-red rather than visible range.

23. Originally Posted by question for you
Originally Posted by Strange
Originally Posted by question for you
But why do dropplets appear coloured on mass in rainbows instead of lots of tiny rainbows?
Have you ever bounced a ball off the angle between the floor and a wall? It always bounces back towards you, whatever angle you throw it at.

A ball doesn't always bounce back to you from a floor/wall joint. If you were inside a sphere it would always come back to you.

This diagram doesn't explain how we see a thick band of violet, then indigo then aquamarine or whatever they are called up to red, in the sky in front of us.
It does if you think about it a bit. If you follow the white band of light, it will lead back to the sun. The red band at 42 degrees leads to your eye. This means that the only droplets you will see emitting red light are the droplets precisely 42 degrees between the sun and your eye, and the droplets at that positon can only reflect red to you. All other colors will be reflected at a slightly different angle, The ones reflecting violet to your eye will be at a slightly lesser angle to the sun.
A 7 metre thick rainbow in the sky is not projected from one single prism. How can all those rain drops act as a single prism producing clearly defined and thick bands of colour in the sky?
The color bands are not really clearly defined. It's a continuous spectrum. Your eyes are just trained to see it as discrete colors.

24. yeh
that's kinda why the question,
as the atmosphere heats up and changes the angles of the h and o bonds, or stretches one ho bond, or both h-o bonds,
---then releases this energy as it "snaps back" and the energy then radiates toward earth, space, or another H2O molecule, and bends or stretches it, and the more heat the more bent or stretched molecules, and so it goes---------
so, this gathering of greater numbers of bent molecules grows to some point of stability?
then if the preponderance of atmospheric water vapor is bent and or stretched molecules, do we effectively have change in the greater refractive index

is there a limit to the bending and stretching---and how much heat is required to hit that limit---are we anywhere near that limit now?
............
I suspect that the bending would be the most important for changing the refractions?

but, all is a guess.

25. Originally Posted by question for you
Whats so special about the visible spectrum I wonder. What is it about us that interprets this part of the spectrum the way it does? And why not perceive other parts of the spectrum?
The visible spectrum is the peak of the sun's intensity. Perceiving other parts of the spectrum would come at the cost of less sharpness of focus (unless you had many eyes for the different parts of the spectrum). Each wavelength is focused at a slightly different focal length. It's called chromatic aberration.
Chromatic aberration - Wikipedia, the free encyclopedia

26. Originally Posted by Strange
Originally Posted by question for you
What has the amount a frequency of EM radiation slows down by got to do with the angle it reflects from a prism, or surface of a material?
When the light hits the boundary and slows down, it causes it to change direction
How does slowing down cause a change in direction? surely it's the angle of the surface of the material which is causing the change in direction?

Originally Posted by Strange
In what way does it 'slow down'?
The classical (light as wave) explanation is that the permeability and permittivity (two properties of a material) change which changes the speed of light in the material (like making a liquid thicker - as a poor analogy).

The more modern explanation involves quantum electrodynamics (QED) which I am not even going to attempt to explain (but there are some good videos on line of Feynman doing a series of non-technical lectures, which are worth watching).
I can imagine that light is slowed as it passes through a transparant material. I meant, the speed at which photons are travelling through space or the speed which they are vibrating 'within themselves'? or both?

Surely it's the angle of the surface that refracts light?

Originally Posted by Strange
Whats so special about the visible spectrum I wonder. What is it about us that interprets this part of the spectrum the way it does? And why not perceive other parts of the spectrum? Insects do. Don't tell me... it's because we didn't need it in our evolution.
Exactly. The same reason that the hole that a puddle sits in is exactly the same shape as the water.
I think you're confusing evolution with surface permiability and fluid dynamics under gravitational forces.

Originally Posted by Strange
What is actually happening, is it that our nuerons can only 'resonate' with this small part of the spectrum? do the EM frequencies of the rainbow correspond to the EM frequencies of the biological body or part of the brain resonsible for sight?
Kinda. There are proteins in the the eye which respond to different wavelengths of light (you can think of them as red, green and blue but they are more like yellowish, greenish and blue). When these absorb light they generate a signal which is sent to the brain. The brain then generates all the colours we see from this crude information.

Other animals are sensitive to different ranges of frequencies and some have more than three types of colour-sensitive receptor. (Depending on their evolutionary needs.)
So the receptors are proteins? 3 different types of protein which respond to 3 parts of the visible spectrum?
Do you know the name and molecular structure of these proteins? Do all the amines go into the makeup of these proteins?

Originally Posted by sculptor
so,
you sumed it up nicely
..
which raises a question that maybe you can answer
when CO2 molecules are excited by various light frequencies, they stretch, or bend, or twist based on the frequency of the spectrum.
assuming that water does the same(stretching mostly at the higher frequencies, and bending at the lower, does this effect the refractive index?
When you say excited is this the same as heated? charging the molecules with energy.

Now i'm imaging that what we're seeing is the result not of light refracting from dropplets but of photons bouncing off ellectrons in atoms. Is that plausible?

Anyway, I still don't get rainbows.

27. Originally Posted by Harold14370
Originally Posted by question for you
But why do dropplets appear coloured on mass in rainbows instead of lots of tiny rainbows?
If you follow the white band of light, it will lead back to the sun. The red band at 42 degrees leads to your eye. This means that the only droplets you will see emitting red light are the droplets precisely 42 degrees between the sun and your eye, and the droplets at that positon can only reflect red to you. All other colors will be reflected at a slightly different angle, The ones reflecting violet to your eye will be at a slightly lesser angle to the sun.
What variation in degree are we talking about between each colour?
This relates to the broadness of the rainbow in relation to it's distance from the observer? variation in degrees of refraction x distance from cloud/Pi = rainbow thickness?

Somebody may have attempted to explain this, if so I apologise, what causes the different frequencies to refract at different angles? They are all basically reflecting off atoms on the surface of a dropplet. Why does the prism 'twist'/reverse the spectrum of light? and why does the white light 'broaden out' as it appears to from the diagram.

Originally Posted by Harold14370
A 7 metre thick rainbow in the sky is not projected from one single prism. How can all those rain drops act as a single prism producing clearly defined and thick bands of colour in the sky?
The color bands are not really clearly defined. It's a continuous spectrum. Your eyes are just trained to see it as discrete colors.[/QUOTE]

True they do all blend in to each other.

I wouldn't say our eyes are trained, they are made to do it. They are made and trained.

28. Originally Posted by question for you
What variation in degree are we talking about between each colour?
This relates to the broadness of the rainbow in relation to it's distance from the observer? variation in degrees of refraction x distance from cloud/Pi = rainbow thickness?
According to the Wikipedia article " The light leaving the rainbow is spread over a wide angle, with a maximum intensity at 40.89–42°." Which I guess would make the rainbow a bit over 1 degree in width.
Somebody may have attempted to explain this, if so I apologise, what causes the different frequencies to refract at different angles? They are all basically reflecting off atoms on the surface of a dropplet. Why does the prism 'twist'/reverse the spectrum of light? and why does the white light 'broaden out' as it appears to from the diagram.
No, it's not just reflection. It's also refraction, which depends on the refractive index, which varies by wavelength. The white light is shown in the diagram with some width because the sun is not a point source. The sun's disc subtends a noticeable angle. It is shown refracting into its constituent colors as it enters the water droplet.

29. I will point out that everything discussed so far is covered in the Wiki article.

30. Originally Posted by question for you
How does slowing down cause a change in direction? surely it's the angle of the surface of the material which is causing the change in direction?
Yes, it is the slowing down at an angle. If you think about it, the first bit of the edge to hit the surface slows down which lets the next bit catch up with it, and so on all along the waverfront. This is what causes it to change direction.

I can imagine that light is slowed as it passes through a transparant material. I meant, the speed at which photons are travelling through space or the speed which they are vibrating 'within themselves'? or both?
It is the speed at which the wavefront moves through the material. (Just to confuse things for you, photons always move at c).

Do you know the name and molecular structure of these proteins? Do all the amines go into the makeup of these proteins?
I have no idea. Would you like me to and read the Wikipedia page on human vision and summarise it for you?

Now i'm imaging that what we're seeing is the result not of light refracting from dropplets but of photons bouncing off ellectrons in atoms.
Photons do not "bounce off" electrons. Remember: Feynman ... video ... QED ... Google ...

31. Originally Posted by AlexG
I will point out that everything discussed so far is covered in the Wiki article.

What you think my mum is here reading out user's comment for me? no, I'm reading them independently.

I dislike wiki pedia and find it a time consuming way of learning. Usually it suits me better to ask questions... I have looked through a wiki page on rainbows and a few other pages on aspects of the phenomena. The fact is I have learnt a lot more from discussing with people here. I do hope you are able to grasp this fact for once and for all. If you pipe up with any more of your unhelpful comments I cannot promise I will be able to remain civil with you. Good day.

32. Originally Posted by Strange
Originally Posted by question for you
How does slowing down cause a change in direction? surely it's the angle of the surface of the material which is causing the change in direction?
Yes, it is the slowing down at an angle. If you think about it, the first bit of the edge to hit the surface slows down which lets the next bit catch up with it, and so on all along the waverfront. This is what causes it to change direction.
Not understood. Understood that one side of the light hits the surface first... how this causes a catching up or a change in direction I don't understand.

Originally Posted by Strange
I can imagine that light is slowed as it passes through a transparant material. I meant, the speed at which photons are travelling through space or the speed which they are vibrating 'within themselves'? or both?
It is the speed at which the wavefront moves through the material. (Just to confuse things for you, photons always move at c).
Whats the point in confusing me? why not explain this and explain how or why you claim that the light slows down?

Originally Posted by Strange
I have no idea. Would you like me to and read the Wikipedia page on human vision and summarise it for you?
Thats a very kind offer, I think it would help... but it isn't fair on you and I reckon there is a risk that much was lost by the person who filled out a long winded wiki page... and more will be lost in translation by you, what I really need is not somebody who churns out text book answers in an accademic style, but somebody who really understands what is going on. They would be able to cut through the crap and explain in plain english.

Feyman video QED gottcha...

33. Originally Posted by Harold14370
Originally Posted by question for you
What variation in degree are we talking about between each colour?
This relates to the broadness of the rainbow in relation to it's distance from the observer? variation in degrees of refraction x distance from cloud/Pi = rainbow thickness?
According to the Wikipedia article " The light leaving the rainbow is spread over a wide angle, with a maximum intensity at 40.89–42°." Which I guess would make the rainbow a bit over 1 degree in width.
I didn't remember noticing 40.89.

Light leaving the rainbow??? Light leaving each prism? So the light is reflected and spread into it's component parts... the colour we see depends on our precise angle in relationto the sun and dropplet.

Ok... Moving on a little.

With any form of colour, mixing together the colours of the rainbow does not make bright white.

How is it that we see all these frequencies or waveforms combined as 'normal light' but only see each component when refracted?

Why do we not see the component colours anyway? Of course we can when certain component colours are reflected of a surface, but not until then.

What is it about a surface that only reflects a certain part of the visible spectrum and absorbs the rest?

34. Originally Posted by question for you
Not understood. Understood that one side of the light hits the surface first... how this causes a catching up or a change in direction I don't understand.
Take a stick, hold it at each end, and move both ends at the same speed. It goes in a straight line. Now move one end slower then the other. What happens?

Whats the point in confusing me? why not explain this and explain how or why you claim that the light slows down?
Feynman ... video ...

Thats a very kind offer, I think it would help...
It was sarcasm. But never mind.

35. Originally Posted by question for you
With any form of colour, mixing together the colours of the rainbow does not make bright white.
Yes it does. One of the things Newton did was to put the spectrum back through a prism oriented the other way round. White light came out.

Here is an example of colour mixing:
RGB_illumination.jpg

What is it about a surface that only reflects a certain part of the visible spectrum and absorbs the rest?
Two reasons (that I know of). The electrons in the atoms of the material absorb some frequencies and not others. The surface structure causes diffraction effects so that certain frequencies are cancelled and others reinforced. The latter is how many animals (butterflies, for example) create their bright colours.

36. Originally Posted by Strange
Originally Posted by question for you
Not understood. Understood that one side of the light hits the surface first... how this causes a catching up or a change in direction I don't understand.
Take a stick, hold it at each end, and move both ends at the same speed. It goes in a straight line. Now move one end slower then the other. What happens?
Is that really supposed to mean something? What is the purpose of this 'explaination'?

The question is why does light change direction when hitting a surface at a ertain angle? I'd be very suprised if the answer has anything to do with holding a stick.

Originally Posted by Strange
Whats the point in confusing me? why not explain this and explain how or why you claim that the light slows down?
Feynman ... video ...
I'm on the second vid... not getting muh from it. Hasn't anybody illustrated it with CAD yet?

Originally Posted by Strange
It was sarcasm. But never mind.
No! really?

37. Originally Posted by Strange
Originally Posted by question for you
With any form of colour, mixing together the colours of the rainbow does not make bright white.
Yes it does. One of the things Newton did was to put the spectrum back through a prism oriented the other way round. White light came out.

Here is an example of colour mixing:
RGB_illumination.jpg
I meant to say colours of the rainbow in any form... except light. For example, when we mix paint colours of the rainbow... we get brown, not bright light.

Explain.

Originally Posted by Strange
What is it about a surface that only reflects a certain part of the visible spectrum and absorbs the rest?
Two reasons (that I know of). The electrons in the atoms of the material absorb some frequencies and not others. The surface structure causes diffraction effects so that certain frequencies are cancelled and others reinforced. The latter is how many animals (butterflies, for example) create their bright colours.
So the electrons do reflect some of the light.

It's the frequency of the electron which affects which light it reflects? How does this work? An electron reflects the colours which resonate at the same frequency as itself? or it absorbs those colours and reflects frequencies that don't match it's frequency?

38. Originally Posted by question for you
The question is why does light change direction when hitting a surface at a ertain angle? I'd be very suprised if the answer has anything to do with holding a stick.
Look at the diagram. The stick is supposed to represent a wavefront. If you move one end slower than the other, the stick will rotate.

39. Originally Posted by question for you
I meant to say colours of the rainbow in any form... except light. For example, when we mix paint colours of the rainbow... we get brown, not bright light.

Explain.
Yes, sir!

colour.jpg

So the electrons do reflect some of the light.
No. Feyman. QED. Video ... Or he has written a book, which is much more accessible if you prefer the written word.

It's the frequency of the electron which affects which light it reflects? How does this work?
It is related to the available energy levels of the electrons. I am not going any further as this gets into things that require a degree in solid state physics or physical chemistry.

40. Originally Posted by Strange
Originally Posted by question for you
The question is why does light change direction when hitting a surface at a ertain angle? I'd be very suprised if the answer has anything to do with holding a stick.
Look at the diagram. The stick is supposed to represent a wavefront. If you move one end slower than the other, the stick will rotate.
A) What diagram?
B) What about a stick rotating?

You have a flat peice of glass laying horizontally in mid air. The sun is appears to be at around 42 degrees above the horizon... the light of the sun hits the surface of the glass, which reflects light in all directions. The bulk of the light goes through the layer of glass and changes it's direction... what causes the change in direction?
It changes due to the surface of the material... earlier you tried to explain that it is due to permiation and permivitty of the material, or something.

The light only seems to change direction when it hits a surface of a material... How does the wave front hitting the surface at an angle cause the wave front to change direction? Why does it not just pass straight through?

What is the equation or formular for how much a wave front will change direction in relation to the angle of a surface?

41. Originally Posted by Strange
Originally Posted by question for you
I meant to say colours of the rainbow in any form... except light. For example, when we mix paint colours of the rainbow... we get brown, not bright light.

Explain.
Yes, sir!

colour.jpg
Good work private!

Originally Posted by Strange
It's the frequency of the electron which affects which light it reflects? How does this work?
It is related to the available energy levels of the electrons. I am not going any further as this gets into things that require a degree in solid state physics or physical chemistry.
Some monkey brain was telling me earlier that I could answer all my questions by reading wikipedia...

Looks like I might need a degree a two... or a bloody good egg who has done the degree already and enjoys enlightening people.

42. Originally Posted by question for you
Originally Posted by Strange
Originally Posted by question for you
The question is why does light change direction when hitting a surface at a ertain angle? I'd be very suprised if the answer has anything to do with holding a stick.
Look at the diagram. The stick is supposed to represent a wavefront. If you move one end slower than the other, the stick will rotate.
A) What diagram?
B) What about a stick rotating?
From post #19:
When the light hits the boundary and slows down, it causes it to change direction:
Refraction-Water-Waves.gif
(That diagram uses the change in speed in water due to a change in depth, but it is the same thing.)

You have a flat peice of glass laying horizontally in mid air. The sun is appears to be at around 42 degrees above the horizon... the light of the sun hits the surface of the glass, which reflects light in all directions.
It doesn't reflect in all directions. (well, a little bit goes in all directions but it is a specular surface so nearly all of it is reflected at the same angle that it is incident)

The bulk of the light goes through the layer of glass and changes it's direction... what causes the change in direction?
Refraction. See above.

It changes due to the surface of the material... earlier you tried to explain that it is due to permiation and permivitty of the material, or something.

The light only seems to change direction when it hits a surface of a material... How does the wave front hitting the surface at an angle cause the wave front to change direction? Why does it not just pass straight through?
See above.

What is the equation or formular for how much a wave front will change direction in relation to the angle of a surface?
Originally Posted by Wikipedia
Snell's law states that the ratio of the sines of the angles of incidence and refraction is equivalent to the ratio of phase velocities in the two media, or equivalent to the reciprocal of the ratio of the indices of refraction:

43. Originally Posted by Strange
Look at the diagram. The stick is supposed to represent a wavefront. If you move one end slower than the other, the stick will rotate.
From post #19:
When the light hits the boundary and slows down, it causes it to change direction:
Refraction-Water-Waves.gif
(That diagram uses the change in speed in water due to a change in depth, but it is the same thing.[/QUOTE]

I don't get anything from that diagram... tell me what am I supposed to learn from that? It illustrates nothing new to me. The deep water/shallow water thing makes it even more baffeling... All it shows is that light refracts from a surface. We have establish that happens, it's why and how i'm interested in.

Originally Posted by Strange
You have a flat peice of glass laying horizontally in mid air. The sun is appears to be at around 42 degrees above the horizon... the light of the sun hits the surface of the glass, which reflects light in all directions.
It doesn't reflect in all directions. (well, a little bit goes in all directions but it is a specular surface so nearly all of it is reflected at the same angle that it is incident0.
That's what I said!
if it's specular then a lot of the light will be reflected off the surface rather than refracted through it.

Originally Posted by Strange
The bulk of the light goes through the layer of glass and changes it's direction... what causes the change in direction?
See refraction above
I've seen refraction, I've seen the diagram above. I stiil don't know, hence my asking.

Please if you can... explain in a sentance why the lights direction changes when it refracts through a surface.

Originally Posted by Strange
Originally Posted by Wikipedia
Snell's law states that the ratio of the sines of the angles of incidence and refraction is equivalent to the ratio of phase velocities in the two media, or equivalent to the reciprocal of the ratio of the indices of refraction:
That's greek to me... I will look up those technical terms.

44. Originally Posted by question for you
I don't get anything from that diagram... tell me what am I supposed to learn from that? It illustrates nothing new to me. The deep water/shallow water thing makes it even more baffeling... All it shows is that light refracts from a surface. We have establish that happens, it's why and how i'm interested in.
It is caused by the change in velocity. If you can't visualise it, I don't know what I can do. Except suggest a practical demonstration. But you didn't like that either. <shrug>

That's what I said!
if it's specular then a lot of the light will be reflected off the surface rather than refracted through it.
No you said it would be reflected in all directions. That would be diffuse reflection, not specular.

The reflection from a plane of glass is specular, even though most of it is not reflected.

45. Originally Posted by question for you
I don't get anything from that diagram... tell me what am I supposed to learn from that? It illustrates nothing new to me. The deep water/shallow water thing makes it even more baffeling... All it shows is that light refracts from a surface. We have establish that happens, it's why and how i'm interested in.
Analogy: Imagine an M1Abrams (Tank) moving in a straight line. If you pull back on the left lever, the left tracks will decrease speed. Press forward on the right lever and the right tracks increase speed. This is how a tank turns.
When light hits a medium, the phase velocity changes but the frequency remains the same.

46. Ah, yes. A tank. I was trying to think of something that is steered by changing the speed of the wheels....

47. Originally Posted by Strange
It is caused by the change in velocity. If you can't visualise it, I don't know what I can do. Except suggest a practical demonstration. But you didn't like that either. <shrug>
I think I missed the bit where you posted a webcam clip of you practically demonstrating how a wave front refracts.

Originally Posted by Strange
The reflection from a plane of glass is specular, even though most of it is not reflected.
Light from a mirror is specular reflection?
light does reflect difusely ... and specular-ly.

48. Originally Posted by question for you
[Light from a mirror is specular reflection?
light does reflect difusely ... and specular-ly.
Exactly.

49. Originally Posted by Neverfly
Analogy: Imagine an M1Abrams (Tank) moving in a straight line. If you pull back on the left lever, the left tracks will decrease speed. Press forward on the right lever and the right tracks increase speed. This is how a tank turns.
When light hits a medium, the phase velocity changes but the frequency remains the same.
I can ofcourse imagine a tank changing direction, and light changing directions... I'm struggling with the parralels between the two.

Are we saying a wave front is a rigid line or band which cannot bend, much like a tanks chassis... so when the ultraviolet 'track' is slowed by a material (even though light always travels at speed of light and so doesn't slow), the UV is 'stuck' for a split second until the infared also hits the surface, at which oint both the uv track, the infared track and all the tracks of the spectrum in between... are free to roll on in a forward direction? Is that what we'r saying?

If so, What keeps the wave front in this rigid structure that doesn't bend or allow for different wave within the front to move at different speeds?

How is it possible for the UV to sit and wait until the infared has made it round the corner?

Also, if it was simply a case of a wave front, stopping and turning like a tank... then why doesn't the wave front continue as it was after the 'turn', why does it seperate/disperse the wave front into it's component waves?

50. Originally Posted by question for you
If so, What keeps the wave front in this rigid structure that doesn't bend or allow for different wave within the front to move at different speeds?
The wavefront is normally moving at the same speed and so it retains its shape (which is a segment of a circle - think ripples on a pond - but for sunlight can be considered a straight line). When part of it is slowed down, the next bit (which is still moving faster) gains on it a bit. Then that bit slows down and the next bit gains on it. This causes the whole thing to "slew round" and then continue in the new direction.

How is it possible for the UV to sit and wait until the infared has made it round the corner?
It doesn't they are independent.

Also, if it was simply a case of a wave front, stopping and turning like a tank... then why doesn't the wave front continue as it was after the 'turn', why does it seperate/disperse the wave front into it's component waves?
Each frequency has its own wavefront. These are slowed by different amounts and therefore turn by different amounts. Therefore each colour comes out at a slightly different angle.

51. Originally Posted by question for you
Originally Posted by Neverfly
Analogy: Imagine an M1Abrams (Tank) moving in a straight line. If you pull back on the left lever, the left tracks will decrease speed. Press forward on the right lever and the right tracks increase speed. This is how a tank turns.
When light hits a medium, the phase velocity changes but the frequency remains the same.
I can ofcourse imagine a tank changing direction, and light changing directions... I'm struggling with the parralels between the two.

Are we saying a wave front is a rigid line or band which cannot bend, much like a tanks chassis... so when the ultraviolet 'track' is slowed by a material (even though light always travels at speed of light and so doesn't slow), the UV is 'stuck' for a split second until the infared also hits the surface, at which oint both the uv track, the infared track and all the tracks of the spectrum in between... are free to roll on in a forward direction? Is that what we'r saying?

If so, What keeps the wave front in this rigid structure that doesn't bend or allow for different wave within the front to move at different speeds?

How is it possible for the UV to sit and wait until the infared has made it round the corner?

Also, if it was simply a case of a wave front, stopping and turning like a tank... then why doesn't the wave front continue as it was after the 'turn', why does it seperate/disperse the wave front into it's component waves?
At this point, stop thinking of Light as a solid Wave. Let's talk Photons.

Photons demonstrate wave and particle qualities. Which is where this topic gets interesting.

Light always moves at c. Always- it does not slow down.
Light moves at c in a vacuum and light moves at c in a medium.

Well, what's this about it slowing down to refract, then? It doesn't slow down, it just gets distracted for a moment.

When a photon hits a medium, it is absorbed, putting an electron in the atom in an excited state. When it drops down to a lower energy state, it must emit a photon since energy can be neither created nor destroyed.
And that distraction takes a brief moment of time.

52. Originally Posted by Strange
The wavefront is normally moving at the same speed and so it retains its shape (which is a segment of a circle - think ripples on a pond - but for sunlight can be considered a straight line). When part of it is slowed down, the next bit (which is still moving faster) gains on it a bit. Then that bit slows down and the next bit gains on it. This causes the whole thing to "slew round" and then continue in the new direction.
So is a bow... heading this way >)? but if this hits a surface at an angle like so: >)/.... Then it seems that it may not even be the UV which hits the surface first, it might be indigo. Then uv and blue hit at the same time,, then green, then yellow then orange then red. In a prism any diference in speed of distance travel by the light would be altered on first surface, then realigned on second surface, due to the flip/rotation shown in a prism diagram.

But then you still havent explained how you can claim that the different frequencies of light can slow down, and yet light is always travelling at the speed of light. Which begins to seem like this is nothing more than a hypothetical explaination which doesn't conform to another more robust hypothetical explaination.

Is the light slowing down through the rain drop or is it constantly moving at speed of light?

We've been speaking about a beam of EM radiation, this is presumably a single point of a massive wave that travels in every direction N,S,E,W in 4d dimensional space and time.
This beam consists of every freuency on the EM spectrum at all times unless filtered or reflected/defracted by space and or the atmosphere.

In what way can this 'beam' be considered a 'wave front' does each 'wave front' have a specific dimension? specifically 2d width and hiegth? and the 3rd D, depth? we already know about it's 4thD, the speed of light (which you just need to clarify in terms of, does it slow down or not?).

This 'wave front' which i'm not sure is a thing, it could be another analogy, has a wave, or a photon? at every frequency of the EM spectrum. How do these different frequency waves? or photons? interact or share the same space as each other?

Do they lock within each other? Does one frequency of EM radiation have an effect on any other frequencies? Do they all travel at the same speed before defraction?

Strange feel free to give a monologue if you like. try to avoid analogies unless it can be explained how the analogy differs from reality. I want to be able to picture aspects of the real thing in my mind, not people twisting sticks or tanks turning corners.

Originally Posted by question for you
How is it possible for the UV to sit and wait until the infared has made it round the corner?
It doesn't they are independent.[/QUOTE]

Then the stick and tank analogies are completely inacurate to describe what is happening except on a very basic level.

I don't need an analogy to show me that the light changes direction 'like a tank'... I'm searching for a more detailed understanding of what exactly is happening and more importantly how and why it's happening. Though I don't mean to sound ungrateful to any of you who have tried to help explain, I appreciate your efforts. Thank you.

Originally Posted by question for you
Also, if it was simply a case of a wave front, stopping and turning like a tank... then why doesn't the wave front continue as it was after the 'turn', why does it seperate/disperse the wave front into it's component waves?
Each frequency has its own wavefront. These are slowed by different amounts and therefore turn by different amounts. Therefore each colour comes out at a slightly different angle.[/QUOTE]

See above... Slowed? really? then they are not travelling at speed of light?

When you say each frequency has it's own wavefront... are you speaking of a wave front that radiates from the source in 3D 'ripples'? Or do you mean that each 'photon' beam (each tiny unit of EM radiation) is itself a tiny wave front that combines with all the other tiny wavefronts to form the 3D 'ripple' from the source?

If/when you clear up the messy bussiness about the frequencies of light being slowed by different amounts, and yet always travelling at the speed of light, then please enter a snippet about why a material such as glass will cause a velocity change in wave fronts, and why that velocity change causes a change in the lights direction.
It must have something to do with photon/electron interaction...?

It would be nice to understand about these 'wave fronts'... they are photons? wave/partical dualities? And the frequency of the 'package' relates to how highly charged the photon is?

53. Originally Posted by question for you
So is a bow... heading this way >)? but if this hits a surface at an angle like so: >)/.... Then it seems that it may not even be the UV which hits the surface first, it might be indigo. Then uv and blue hit at the same time,, then green, then yellow then orange then red.
It doesn't matter what order they hit the surface (if that even makes any sense as we are considering continuous waves). It is just the fact they all got rotated through different angles.

In a prism any diference in speed of distance travel by the light would be altered on first surface, then realigned on second surface, due to the flip/rotation shown in a prism diagram.
That is true for a flat piece of glass because the light hits the second surface at the same angle and everything gets rotated back as it was: no separation. The surfaces of a prism are angled so the separation is increased by the second surface.

But then you still havent explained how you can claim that the different frequencies of light can slow down, and yet light is always travelling at the speed of light.
The speed of light in a vacuum is constant. It is always slower in a medium. The amount by which it is slower is a function of frequency. That is the "classical" explanation.

The other answer is the one that Neverfly alluded to: the photons always travel at c but they get delayed a little every time they are absorbed and released by an electron. That opens up all sorts of extra questions to which my only answer is: QED ... Feynman ... video ...

Is the light slowing down through the rain drop or is it constantly moving at speed of light?
It slows down (if you are happy with the classical model).

This beam consists of every freuency on the EM spectrum at all times unless filtered or reflected/defracted by space and or the atmosphere.
If we are talking about sunlight then it consists of a small range of radiation mainly in the visible spectrum.

In what way can this 'beam' be considered a 'wave front' does each 'wave front' have a specific dimension?
Pond. Ripple. Swiming pool. Wave machine. Think of the peak of the electromagnetic wave like that.

Does one frequency of EM radiation have an effect on any other frequencies?
No they are all independent. (There are a few very special cases where you can get light of a particular frequency to change the refractive index of a material for another frequency.)

Do they all travel at the same speed before defraction?
REfraction. Yes.

Then the stick and tank analogies are completely inacurate to describe what is happening except on a very basic level.
I think they are both good analogies for what causes a wave to change direction when its speed is changed.

54. Originally Posted by Neverfly
At this point, stop thinking of Light as a solid Wave. Let's talk Photons.

Photons demonstrate wave and particle qualities. Which is where this topic gets interesting.
You will see from my last post which I posted befor I saw this one... That I have just moved it on to photons myself, great minds think alike Neverfly.

Originally Posted by Neverfly
Light always moves at c. Always- it does not slow down.
Light moves at c in a vacuum and light moves at c in a medium.

Well, what's this about it slowing down to refract, then? It doesn't slow down, it just gets distracted for a moment.

When a photon hits a medium, it is absorbed, putting an electron in the atom in an excited state. When it drops down to a lower energy state, it must emit a photon since energy can be neither created nor destroyed.
And that distraction takes a brief moment of time.
Thats an excellent explaination... the photons don't slow down, they just mess around orbiting with an atom/electron for a period.

How many photons can a silica atom absorb? and for how long? How many photons could you fire into a sheet of glass before the atoms become 'saturated' and eject the photons start out the other side?

So, What is happening with this 'distraction'? A photon is being caught up in eletron charge? A photon is giving energy to the electron/atom? in this case the photon would lose energy? How can an atom/electron absorb a photon?

Anyway... more photons come along and the electrons are at max capacity so the photons are ejected (at all angles?). When we see photons reflecting(?) from electrons in the surface of a peice of glass or water dropplet, we only see a particular colour when we are at a particular angle. This means in my mind that an atom/electron is reflecting all EM radiation, in all directions, It's like the EM radiation is entering the atom/electron/prism at the same time and it being ejected or reflected in a vary ordered way. Amazing. So now I need to get to grips with why certain EM frequencies are reflected/refracted at certain angles and other's at other angles... Why the ordering of EM radiation into segments?

Also... is an atom a prism? do photons hit the surface/atmosphere of an atom and refract?

55. Originally Posted by Strange
I think they are both good analogies for what causes a wave to change direction when its speed is changed.
Ok... So we are being saturated with EM waves travelling in nearly all directions through the universe. As far as we can tell the EM wave patterns are not interfering with each other, almost like they are supposed to be in different dimensions within the same space time.

The thing with a wave is that it travels through a substance... water particals do not go from mid pacific to los Angeles as a wave... they generally bob up and down, up and down and this en masse causes what we percieve as a wave. Is it a similar thing with photons? Do they push each other along in waves? Passing energy from one to the other like water molecules do? I'm sure the answer is going to be no, but it seems more probable than thinking of a photon as a tiny thing that travels from the sun to here balistically in 8 minutes.

Is there a 'substance' that EM waves travel through? Much like water is the substance that 'gravitational' force makes waves travel through, and Air is the substance that sound waves travel through.

When a wave that carries through water hits a permiable barrier, some reflects at a specular angle (right?), bouncing off, and some permiates... does that which permiates refract in the same way as light through glass?

56. Originally Posted by question for you
Is there a 'substance' that EM waves travel through? Much like water is the substance that 'gravitational' force makes waves travel through, and Air is the substance that sound waves travel through.
Not unless you think of the electromagnetic field as a "substance". There is a varying electric field which induces a changing magnetic field which induces a changing electric field ....

When a wave that carries through water hits a permiable barrier, some reflects at a specular angle (right?), bouncing off, and some permiates... does that which permiates refract in the same way as light through glass?
Pretty much. As you saw in that earlier diagram, there is an equivalent to the change in speed causing refraction when the depth changes.

57. Originally Posted by Strange
Originally Posted by question for you
Is there a 'substance' that EM waves travel through? Much like water is the substance that 'gravitational' force makes waves travel through, and Air is the substance that sound waves travel through.
Not unless you think of the electromagnetic field as a "substance". There is a varying electric field which induces a changing magnetic field which induces a changing electric field ....
I do think of EM radiation as substance. When you say feild do you mean ocean that is everywhere in space? or do you mean feild of radiation emiting from a source that ends as soon as the source stops? An EM radiation feild? or a tranquil feild upon which EM radiates?

This catch 22 varying electric/magnetic feild interaction belongs to the earth? plus all other gross matter/energy 'centres' or the universe and all the subtler matter/energy in the universe? which basically means all through space and therefor it is really a comprehensive 'feild'? Or just a limited feild around a mass?

Originally Posted by Strange
When a wave that carries through water hits a permiable barrier, some reflects at a specular angle (right?), bouncing off, and some permiates... does that which permiates refract in the same way as light through glass?
Pretty much. As you saw in that earlier diagram, there is an equivalent to the change in speed causing refraction when the depth changes.
I didn't see that at all from the diagram... I thought it was supposed to be light passing through water.

Why does change in speed cause refraction?

58. Originally Posted by question for you
[I do think of EM radiation as substance. When you say feild do you mean ocean that is everywhere in space? or do you mean feild of radiation emiting from a source that ends as soon as the source stops? An EM radiation feild? or a tranquil feild upon which EM radiates?

This catch 22 varying electric/magnetic feild interaction belongs to the earth? plus all other gross matter/energy 'centres' or the universe and all the subtler matter/energy in the universe? which basically means all through space and therefor it is really a comprehensive 'feild'? Or just a limited feild around a mass?
I suspect you need a degree in physics to understand or explain that sort of thing. I don't have one. And I suspect you don't either.

I didn't see that at all from the diagram... I thought it was supposed to be light passing through water.
No it was a water wave / ripple hitting a change in speed (caused by a change in depth). When I looked for an image, that was the simplest.

Why does change in speed cause refraction?
Haven't we been through all that already. If you can't see from that diagram that as the edge that first hits the surface (or change in depth) will be slowed causing the whole thing to slew round then I don't know how else to explain it.

Try the "marching model" here:Marching model of refraction | Nuffield Foundation

Or an interactive thingy here: NUMB3RS Episode 403: Hollywood Homicide--Wolfram Research Interactive Computations (scroll down to "Scene 5")

59. Originally Posted by question for you
Thats an excellent explaination... the photons don't slow down, they just mess around orbiting with an atom/electron for a period.
Heh, I wouldn't call it 'Orbit' but yeah, it stopped to whistle at a pretty electron.

Originally Posted by question for you
How many photons can a silica atom absorb? and for how long?
Originally Posted by question for you
How many photons could you fire into a sheet of glass before the atoms become 'saturated' and eject the photons start out the other side?
I was trying to be simple but you keep asking questions which require more complexity.
I wouldn't call it orbit and I probably shouldn't call it "absorb" but the word is a bit like an analogy, it usually makes it easier to explain.
The proper description would be easier using Feynman Diagrams and unless you're familiar with them...
Let's try a different word: Interact. An electron will interact with a photon.
Electrons can interact with any amount of photons, there is no limit. So this should answer the two questions above.
Which brings us to your next question:
Originally Posted by question for you
So, What is happening with this 'distraction'? A photon is being caught up in eletron charge? A photon is giving energy to the electron/atom? in this case the photon would lose energy? How can an atom/electron absorb a photon?
A lot of this is described mathematically, such as using the compton formula/or 4-vector with Lorentz Transform. I might call on Physicists on the site to double check what I type here and correct any errors.
This comes into Phase Velocity mentioned above. When a Photon interacts with an electron, the photon "disappears." The energy is transferred to the electron as momenta which excites the electron into a higher energy state. Remember that we must conserve energy, right? So, the momenta total for the photon and the electron must balance out; they must be equal in magnitude. The electron drops into the non-excited state and a photon is emitted, to balance out the equation.
Originally Posted by question for you
When we see photons reflecting(?) from electrons in the surface of a peice of glass or water dropplet, we only see a particular colour when we are at a particular angle.
This is Compton Scattering, where some of the photons energy is transferred to the scattering electron resulting in a decrease in energy>increase in wavelength.
Originally Posted by question for you
Also... is an atom a prism? do photons hit the surface/atmosphere of an atom and refract?
An atom is not a prism. It does not have an "Atmosphere"- thinking with this terms will probably mes you up...
The above should help clarify the interaction.

60. Originally Posted by question for you
I do think of EM radiation as substance.
Well, cut it out.
Originally Posted by question for you
or do you mean feild of radiation emiting from a source that ends as soon as the source stops?
Close enough.
Originally Posted by question for you
Or just a limited feild around a mass?
More like this. It propagates and technically the answer would be "no." But anything at a great distance is negligible and can be ignored for what you're asking right now. Another time, you can delve more deeply into this.
Originally Posted by question for you
Why does change in speed cause refraction?
I'm gonna punch you in the snout.

61. Originally Posted by Neverfly
Originally Posted by question for you
I do think of EM radiation as substance.
Well, cut it out.
But I do because I hear things about a wave/partical duality so often. I see the 'ellementary partical' table which lists EM as 'force carriers', suggesting they have a substance, an essence of matter about them. Isn't the thing about all energy being contained in matter agreeable to physicists?

Sub means under or below or lower than and stance means stand or posture, or position, or station. So substance can mean a thing that is positioned or stationed under or below.

In the case of life EM is everywhere in everything, it undlies life and matter, in every cell and every atom is EM, it does it's thing and supports the existence of life, chemistry happens due to EM interactions right? In this sense it underlies life, it's positioned below everything else in the manisfestation of matter? except maybe other forces like weak force etc... see what you make of that .

Originally Posted by Neverfly
Originally Posted by question for you
Why does change in speed cause refraction?
I'm gonna punch you in the snout.
Now now, you explained the interaction which doesn't change the speed but does delay the journey. Did I get an explaination for this? let me think...an atom or, the surface of a prism reflects the 'bands' of coloured lights most strongly at the angles between 42 and 40.89ish degrees from the sun, which is why if you look at a prism from that angle to the sun, you will see a rainbow.
Ok, the reason the light changes direction through a surface... not tank tracks, not a stick... erm, because it slows down, because of interaction with electrons. The reason the 'slowing down' or interaction causes a change in direction of the majority of light is... because each photon interacts with electrons in particals and get randomly released on there way? many of them don't interact but bounce straight of fully charged electrons? hence the majority of light being refracted in the same direction?

I really want to know why visible frequencies are focussed between 41.89ish and 42 degrees to the sun, magnified and split into component parts by a prism.
I might of been told but it's a lot to take in.

P.S I was asking strange about change in speed causing refraction in water waves. Thirdly are you suposed to be a lady?

Originally Posted by Neverfly
An atom is not a prism. It does not have an "Atmosphere"- thinking with this terms will probably mes you up...
The above should help clarify the interaction.
By atmosphere I am refering to the electron cloud, the force feild. I'm enquiring about the way in which photons interact with electrons or electron clouds.

62. Originally Posted by question for you
see what you make of that .
Originally Posted by question for you
because each photon interacts with electrons in particals and get randomly release on there way?
It is not random, it is delayed. This delay causes the "slowing down" effect even though light does not actually slow down. This causes the effect we see as refraction. If it was random, it may have odd timing or add vectors- no- this doesn't happen.
Originally Posted by question for you
I really want to know why visible frequencies are focussed between 41.89ish and 42 degrees to the sun, magnified and split into component parts by a prism.
I may have to re-direct this one back at Strange. I've not really been following this thread very well... I kinda dove in head first.
Not sure what you're referring to what with the prism and the beboppin' and the Jello Puddin' pops.
Off hand ignorant guess as to what the degrees from the Sun may be about: Light travels in a straight line. Since we're pretty far from the Sun, it's a very narrow bit of light that hits the Earth (Is observed from Earth) as the rest of the Suns light goes past Earth, in other directions from the Earth, etc.

Edit to add: Jeez, I'm a total idiot. Were you referring to the Angle Of Refraction?
Originally Posted by question for you
thirdly are you suposed to be a lady?
Nope.
But if you punch back, remember- so do I.
Originally Posted by Neverfly
By atmosphere I am refering to the electron cloud, the force feild. I'm enquiring about the way in which photons interact with electrons or electron clouds.
Electron cloud works.

63. [QUOTE=Strange;371809]
I suspect you need a degree in physics to understand or explain that sort of thing. I don't have one. And I suspect you don't either.
I'm a secret millionair phycisist who gets kicks out of feigniing ignorance.

Seriously, I'll work it all out one way or another... just such a shame all the previous work is written in a language that I must first study in order to understand.
I might have to kidnapp a physicist or two along the way. 'We have ways of making you speak', sorry bad taste.

Originally Posted by Strange
Why does change in speed cause refraction?
Haven't we been through all that already. If you can't see from that diagram that as the edge that first hits the surface (or change in depth) will be slowed causing the whole thing to slew round then I don't know how else to explain it.

Try the "marching model" here:Marching model of refraction | Nuffield Foundation
We'r still talking about water waves?

My problem with the demonstration is that when the person on the right hits the straight line... they will march on before the others, so the wave is not parallel with the surface but at angle after crossing, relative to the angle that it aproached the line.

64. Originally Posted by Neverfly
Originally Posted by question for you
see what you make of that .
Mine doesn't hurt... it just stops functioning.

Originally Posted by Neverfly
Originally Posted by question for you
because each photon interacts with electrons in particals and get randomly release on there way?
It is not random, it is delayed. This delay causes the "slowing down" effect even though light does not actually slow down. This causes the effect we see as refraction. If it was random, it may have odd timing or add vectors- no- this doesn't happen.
So the interaction is no enough to stop the photon from reflecting at a certain ordered angle, known as angle of refraction.

So the electron photon interaction is responsible for the kink known as refraction?

We need to get into this interaction detail.

Originally Posted by Neverfly
I may have to re-direct this one back at Strange. I've not really been following this thread very well... I kinda dove in head first.
Not sure what you're referring to what with the prism and the beboppin' and the Jello Puddin' pops.
Huh? bebopin Jello pudding? that's highlighted a cultural divide, I have no clue.

You're doing great though, you've been very helpful. yes we were originally talking about rainbows and prism effects.

Originally Posted by Neverfly
Edit to add: Jeez, I'm a total idiot. Were you referring to the Angle Of Refraction?
I think I probably was talking about angle of refraction... I still haven't grasped the ins and outs of it.

Originally Posted by Neverfly
Originally Posted by question for you
thirdly are you suposed to be a lady?
Nope.
But if you punch back, remember- so do I.
It's you that needs to bear in mind the same for me...

I'm releived you're not a lady threatening to knock my block off.

65. Originally Posted by question for you
We'r still talking about water waves?
Either. Waves is waves.

My problem with the demonstration is that when the person on the right hits the straight line... they will march on before the others, so the wave is not parallel with the surface but at angle after crossing, relative to the angle that it aproached the line.
Yes, that's it! When the first person (on the left) hits the boundary they march slower; then the next person and so on. This causes the whole line of people to swing round so it is no longer going in the same direction.

ETA: left in the diagram, right as seen by the people in the row.

66. Originally Posted by Strange
Originally Posted by question for you
We'r still talking about water waves?
Either. Waves is waves..
Waves is things what travels through 'substance' or radiate from something through a substance. If electro magnetic waves don't do that then they must be fundamentality a different thing from water waves surely?

Originally Posted by Strange
My problem with the demonstration is that when the person on the right hits the straight line... they will march on before the others, so the wave is not parallel with the surface but at angle after crossing, relative to the angle that it aproached the line.
Yes, that's it! When the first person (on the left) hits the boundary they march slower; then the next person and so on. This causes the whole line of people to swing round so it is no longer going in the same direction.
I don't think I expressed myself properly.

The first person to hit the 'line', called A, hits the line and starts marching on before B,C and D hit the line and start marching on. Therefore A,B,C and D will not leave the line parralelle or at the same time.

Perhaps the light that refracts in a prism, has been forced to disperse/seperate by this 'changing direction' that is refraction? The wave front of the visible spectrum goes from being 'inline' to be distorted out of line by the refraction. Hencing the visible colours can be seen?

snip 1.PNG

67. Originally Posted by question for you
We need to get into this interaction detail.
I hate tex. With a PASSION. Some people hate snakes. Some people hate spiders.
I hate tex. Hate it hate it hate it. "We need to get into this interaction detail..." he says. BAH!
I was afraid you'd say that... Ok... here we go... Apologies for my tex fumbling. This is like westwind posting images. I hate it.
Pant pant...

q=1800

so, therefore

Remember conservation of energy above. Because energy must be conserved, the electron energy after interacting with the photon (There is no longer a photon, now) would be () and all photon energy has been transferred to the electron.
Now the 4-vector;

So,

Now, let's see what frame speed we need to dopplar shift down to
and
(point of interest, Question_for_You, I officially hate you, right now.)

And the transformation:
Photon GeV:

Electron GeV and MeV:

To revert, reverse sign of

No, never again.

Point is, this is the model. We cannot get down and peer at a photon or an electron. The only way to see it is with the math.

Have I mentioned lately that I freaking HATE tex? Would take all of 10 minutes to do that with pencil and paper. With tex, that took like two hours of fiddling and figuring out how to make the stupid thing display properly hitting Preview like fifty times.

68. Originally Posted by Neverfly
Have I mentioned lately that I freaking HATE tex?
There is an interactive editor you might like: Online LaTeX Equation Editor - create, integrate and download

Or, at least, not hate quite as much.

69. Originally Posted by Neverfly
I hate tex. Hate it hate it hate it. "We need to get into this interaction detail..." he says. BAH!
I was afraid you'd say that... Ok... here we go..
(point of interest, Question_for_You, I officially hate you, right now.)

No, never again.

Point is, this is the model. We cannot get down and peer at a photon or an electron. The only way to see it is with the math.

Have I mentioned lately that I freaking HATE tex? Would take all of 10 minutes to do that with pencil and paper. With tex, that took like two hours of fiddling and figuring out how to make the stupid thing display properly hitting Preview like fifty times.
Neverfly your a soldier, a warrior in the battle of knowledge.

You stood toe to toe with the evils of 'tex' and you conquored that beast, you tamed it, you turned it into your pet. Now you own it, you have mastered it.

It's such a shame I do not understand it, but others may come along and gain form it.

What I do understand from your post is A) we cannot observe photon or electron interaction B) the best theories are made using maths C) it's all rather complicated

So, all in your own time my good man... please begin to explain what this all means

70. Originally Posted by question for you
Neverfly your a soldier, a warrior in the battle of knowledge.
True...
Originally Posted by question for you
You stood toe to toe with the evils of 'tex' and you conquored that beast, you tamed it, you turned it into your pet. Now you own it, you have mastered it.
Let's don't get carried away. It was a fierce battle that left me battered, beaten and bruised. I'll be trying to heal for months. Mastered it? No, I hammered at it til it finally gave in... but it did so with the following warning: "Next time, baby..."

It wasn't what it said.

It was the way it said it.

Originally Posted by question for you
It's such a shame I do not understand it,
See below:
Originally Posted by question for you
What I do understand from your post is A) we cannot observe photon or electron interaction B) the best theories are made using maths C) it's all rather complicated
You just explained the point: You're asking that an answer be given in a form it simply cannot be given. All the "laymans" examples and analogies have been given and you've rejected them all as insufficient. Well, that's kinda the point.
You can't have your cake and eat it, too. No one can hand it all to you. If you want to really understand it, you need to learn and immerse yourself in it. If not, you need to accept the analogies. You cannot really understand it without doin' the learnin.'
So, (Points upward) - there it is. The answer was provided in semi-complete detail. It was demonstrated how the energy transfers to an electron, how that must be conserved and how the photon must be emitted to obey conservation. I can't do it any better, it's all I got.

Originally Posted by question for you
So, all in your own time my good man... please begin to explain what this all means
I just did You can be met halfway, but cannot be carried all the way. You must choose now, how important the concepts are to you and how willing you are to carry on.

71. Originally Posted by Neverfly
Originally Posted by question for you
You stood toe to toe with the evils of 'tex' and you conquored that beast, you tamed it, you turned it into your pet. Now you own it, you have mastered it.
Let's don't get carried away. It was a fierce battle that left me battered, beaten and bruised. I'll be trying to heal for months. Mastered it? No, I hammered at it til it finally gave in... but it did so with the following warning: "Next time, baby..."

It wasn't what it said.

It was the way it said it.
You have shown great graciousness in victory. Not for you the arrogant boasts of a man who knew how close he came to defeat. You humility will stand you in good stead for the next battle, and the next... the war will be yours for the taking. Just when you win the war... there will be a much better peice of software for you to conquor. You will have to train your sons well if your lineage is to remain in control of the situation.

Originally Posted by Neverfly
You can't have your cake and eat it, too. No one can hand it all to you. If you want to really understand it, you need to learn and immerse yourself in it. If not, you need to accept the analogies. You cannot really understand it without doin' the learnin.'
So, (Points upward) - there it is. The answer was provided in semi-complete detail. It was demonstrated how the energy transfers to an electron, how that must be conserved and how the photon must be emitted to obey conservation. I can't do it any better, it's all I got.

You can be met halfway, but cannot be carried all the way. You must choose now, how important the concepts are to you and how willing you are to carry on.
But imerse myself in what? What is the evidence?

Does that maths really explain what is going on? I mean it explains some of it i'm sure... untill we find a new bit of info to put into the equation then we gat completely different answers.

Surely somewhere along the line some kind of electron or photon interaction has been observed with high end technology? Is it just the slit experiment?

The problem with those analogies is that they don't conjour anything that I could consider reality, They don't conjour anything at all except a tank turning and a man holding a stick out. aybe I don't get the analogies because i'm lacking some other vital info... don't know.

I will ofcourse imerse myself in it as much as possible... but I have a whole lot of other mysteries to uncover too. Also ofcourse... I need to make sure I have a good time whilst im alive. It's a balancing act.

72. Originally Posted by question for you
You have shown great graciousness in victory. Not for you the arrogant boasts of a man who knew how close he came to defeat. You humility will stand you in good stead for the next battle, and the next... the war will be yours for the taking. Just when you win the war... there will be a much better peice of software for you to conquor. You will have to train your sons well if your lineage is to remain in control of the situation.
Flattery won't make me go easy on ya in religion debates

But... it can't hurt to try. Keep it up...
Originally Posted by question for you
But imerse myself in what?
The math and physics.
Originally Posted by question for you
What is the evidence?
Originally Posted by question for you
Does that maths really explain what is going on?
Absolutely.
Originally Posted by question for you
I mean it explains some of it i'm sure... untill we find a new bit of info to put into the equation then we gat completely different answers.
Don't assume that just because we do make new discoveries and observations, that all science of today must and will be replaced later. We get some things, right on occasion, too.
For this application, the science is quite solid.
Originally Posted by question for you
Surely somewhere along the line some kind of electron or photon interaction has been observed with high end technology?
The double slit experiment deals with a different phenomena and demonstrates the difficulties in measuring the infinitesimal.
As far as observed, yes, you've observed it first hand. And asked about it.
Originally Posted by question for you
Maybe I don't get the analogies because i'm lacking some other vital info... don't know.
I think it's because you've not been experienced enough in the weird ways of Quantum Mechanics. You're trying to compare behaviors with what is familiar to you. That's why the analogies are used- to relate them in familiar ways.
You're trying to grasp concepts beyond the familiar, at this point which is why I went to the trouble I went to in order to make that demonstration above.
That if you really want to know, you need to buckle down to some serious learning of fundamentals, not just the gist of something, or expect to grasp a complex concept without the base fundamentals to support it.

Originally Posted by question for you
I will ofcourse imerse myself in it as much as possible... but I have a whole lot of other mysteries to uncover too. Also ofcourse... I need to make sure I have a good time whilst im alive. It's a balancing act.
That's not a problem.
All you need to do is open up to the base fundamentals. Then work your way up- see, the entire world follows the same science. Repeatedly. So once you have the basics, you can build on them and more and more and still more keeps coming into focus more clearly for you.

73. Light is comprised of different wavelengths. Blue light has a shorter wavelength and red light has a longer wavelength, and all the colours of the rainbow have wavelengths in between.

When light encounters a medium, like water for instance, those wavelengths interact with the medium. The shorter wavelengths will interact with the medium more than longer wavelengths, over a given distance. Imagine the distance between the top of each wave - there is a shorter distance between the waves in blue light than in red light. The blue waves are all closer together than the red waves. If each wave represents the amount that the light will interact with the medium, then the blue waves will interact more than the red waves.

Each time a wave of light interacts with the atoms in the medium, its direction is changed slightly. This means that the blue waves will change direction more than the red waves, as there is more chance of blue light interacting with the atoms in the medium than red light, due to the waves of blue light being closer together than the waves of red light.

74. Originally Posted by Neverfly
Flattery won't make me go easy on ya in religion debates

But... it can't hurt to try. Keep it up....
Your delude yourself, oh great one, you are as putty in my hands (and very sensual is the experience of moulding you into a work of art).

Originally Posted by Neverfly
All you need to do is open up to the base fundamentals. Then work your way up- see, the entire world follows the same science. Repeatedly. So once you have the basics, you can build on them and more and more and still more keeps coming into focus more clearly for you.
I am very open to that which is new to me... I like physics very much. I just need to find sources of knowledge which are accessible. Maths also I would like to be able to read and understand, this seems less likely.

What will be will be, I will keep my eyes peeled for opportunities. The reason I start these conversations is becuase I can learn what I want to learn from a discussion, I also tend to trust a person I can ask questions of and analyse, more than a book written by who knows who for who knows what reasons.
These discussions are good for me, as long as I can get the right people involved.

75. Originally Posted by question for you
(and very sensual is the experience of moulding you into a work of art)
Sensual?!
Wait, What?
Originally Posted by question for you
I am very open to that which is new to me...
Originally Posted by question for you
I like physics very much.
Now you're trying to get physical with me!
Originally Posted by question for you
I will keep my eyes peeled for opportunities.
I'm sure you will...
Originally Posted by question for you
as long as I can get the right people involved.

...help me please... i is skared.

76. Originally Posted by SpeedFreek
Each time a wave of light interacts with the atoms in the medium, its direction is changed slightly.
But what rules govern the amount that a photons direction changes?

We discussed this a little earlier... the result of the interaction is not random, the light follows a 'ordered' set of physical 'laws' and ends up refrated at a certain angle.

So what is going on when it comes to a change on direction of the photons?

77. Originally Posted by question for you
So what is going on when it comes to a change on direction of the photons?
Sigh...
Take a regular ruler. Like a wooden ruler you would use in school.
Place it on a flat table top so that it's at an angle about 20 degrees to the straight line of the edge of the table.

Start sliding the ruler forward in a straight line, toward the straight edge of the table.

One corner of the ruler is going to meet the tables edge before the other edge.
Make sense?
Now, if that ruler was a beam of light, that edge that met the edge first is going to show that "Slow Down" effect before the other edge, which will still be moving at full speed.
Since that far edge is moving faster now, then the edge that was slowed down, it turns the angle of direction to a new vector.

78. Originally Posted by Neverfly
Originally Posted by question for you
(and very sensual is the experience of moulding you into a work of art)
Sensual?!
Wait, What?
Don't worry, it's just more flattery. Nothing sexual! Just saying that you make a nice plyable medium... * excessive homo erotic inuendo deleted.

Originally Posted by Neverfly
Originally Posted by question for you
I am very open to that which is new to me...
Rainbows are new to me... I have no idea how they occur or why .

Something to do with EM radiation being dispersed by a prism or something... it's all greek to me.

Originally Posted by Neverfly
Originally Posted by question for you
I like physics very much.
Now you're trying to get physical with me!
No inuendo intended... Besides it was you who started threatening to punch me the other day... you ghastly brute.

Originally Posted by Neverfly
Originally Posted by question for you
as long as I can get the right people involved.

...help me please... i is skared.
The right people to answer my questions ofcourse. Such as you, strange and speedfreak.

79. Well, I'm not really up on optics in general, but I gather that the rule is Snell's law, which falls out of Fermat's principle of least time, which falls out of Huygens principle of wave propagation.

In the simplistic way I see it, the "size and spacing" of the atoms in the medium defines how the wavelengths of light interact with that medium.

80. Originally Posted by Neverfly
Originally Posted by question for you
So what is going on when it comes to a change on direction of the photons?
Sigh...
Take a regular ruler. Like a wooden ruler you would use in school.
Place it on a flat table top so that it's at an angle about 20 degrees to the straight line of the edge of the table.

Start sliding the ruler forward in a straight line, toward the straight edge of the table.

One corner of the ruler is going to meet the tables edge before the other edge.
Make sense?
Now, if that ruler was a beam of light, that edge that met the edge first is going to show that "Slow Down" effect before the other edge, which will still be moving at full speed.
Since that far edge is moving faster now, then the edge that was slowed down, it turns the angle of direction to a new vector.
So you say a beam of light has a rigid width to it?

Strange told me that it is not like this.

The beam of light would have to be rigid like a ruler in order for this analogy to be accurate.

81. An analogy is never accurate, which is why it is an analogy.

82. Originally Posted by question for you
So you say a beam of light has a rigid width to it?

Strange told me that it is not like this.

The beam of light would have to be rigid like a ruler in order for this analogy to be accurate.
NO
Jeez
But the ruler shows how one side of the ruler will meet the edge before the other does. It's the same analogy as the tank or as the car moving in a straight line that leads off the road striking sand. It will pull the car to one side- turning it, because one side slowed down before the other because it struck first.

Yes, the analogy is flawed but it gives you the basic idea without the math. If that's not good enough...

Learn the math!

/snarl
/snort
/spit

83. Originally Posted by Neverfly
Originally Posted by question for you
So you say a beam of light has a rigid width to it?

Strange told me that it is not like this.

The beam of light would have to be rigid like a ruler in order for this analogy to be accurate.
NO
Jeez
But the ruler shows how one side of the ruler will meet the edge before the other does. It's the same analogy as the tank or as the car moving in a straight line that leads off the road striking sand. It will pull the car to one side- turning it, because one side slowed down before the other because it struck first.

Yes, the analogy is flawed but it gives you the basic idea without the math. If that's not good enough...

Learn the math!

/snarl
/snort
/spit
No offence fellas... but all this is an analogy of is something turning. I know what turning means. I know what a kink is or a change in direction. I want to know how this physically happens in refraction.

In the case of a ruler, I know how it physicallly happens, the same with a tank.

I still have little clue how it physically happens with light.

P.S the ruler analogy would be good to describe how a tank turns perhaps...

I put it to you guys twice... I think you ignored it: If the red light hits the surface first, then it marches on first (especially considering speedfreaks insight which is that red light interacts less than blue, I think I got that right way round).

So, it is visible from my diagram... what would happen to light.

Surely somebody recognises the genuis of this diagram?

It explains how light does not act like a ruler, or a tank, or a band of marching people with linked arms.

It potentially shows how a wave of light is broken during refraction.

84. Originally Posted by SpeedFreek
Well, I'm not really up on optics in general, but I gather that the rule is Snell's law, which falls out of Fermat's principle of least time, which falls out of Huygens principle of wave propagation.

In the simplistic way I see it, the "size and spacing" of the atoms in the medium defines how the wavelengths of light interact with that medium.
We looked at snell's law.. will check out the others, cheers.

The size and space of atoms is obviously fairly uniform in glass and water dropplets. Therefor and difference in refraction is down to the frequencie of the EM radiation, as you said, short wavelengths interacter more and vice versa.

85. Originally Posted by question for you
No offence fellas... but all this is an analogy of is something turning. I know what turning means. I know what a kink is or a change in direction. I want to how this physically happens.
Learn the math. It's been explained and the Math makes it so much more clear.
Originally Posted by question for you
I still have little clue how it physically happens with light.
I explained it as best I could above, struggling heavily against menacing tex tags. Post 66.
All I can say is believe me, it makes it pretty clear how the physical interaction makes sense.
Originally Posted by question for you

Surely somebody recognises the genuis of this diagram?

It explains how light does not act like a ruler, or a tank, or a band of marching people with linked arms.

It potentially shows how a wave of light is broken during refraction.

The diagram is complete gibberish.

86. Originally Posted by question for you
Originally Posted by SpeedFreek
Each time a wave of light interacts with the atoms in the medium, its direction is changed slightly.
But what rules govern the amount that a photons direction changes?
QED: Feynman video. Or do a PhD in physics.

Originally Posted by question for you
No offence fellas... but all this is an analogy of is something turning. I know what turning means. I know what a kink is or a change in direction. I want to know how this physically happens in refraction.
This is the (simpler) classical description. Wavefront hits the boundary at an angle. The change in speed causes it to turn (for obvious physical reasons: see marching band, tank, ruler, stick analogies). Different frequencies slow by different amounts and so turn by different amounts.

Why does that happen?
QED: Feynman video. Or do a PhD in physics.

87. Originally Posted by question for you
It occurs to me that the answers I seek are not on wikipedia.
why are is there an arch of seperate water droplets that reflect one colour, then another arch of another colour and so on?

.
Hi qfy

Maybe the droplets acts like pixels? It depends on the position of each droplets with respect to viewer
and the angle of source that is round.
I wonder.. if instead of volume of rain shower there is just a curtain of rain fall, will we still the rainbow?

88. Originally Posted by TimeSpaceLightForce
Originally Posted by question for you
It occurs to me that the answers I seek are not on wikipedia.
why are is there an arch of seperate water droplets that reflect one colour, then another arch of another colour and so on?

.
Hi qfy

Maybe the droplets acts like pixels? It depends on the position of each droplets with respect to viewer
and the angle of source that is round.
I wonder.. if instead of volume of rain shower there is just a curtain of rain fall, will we still the rainbow?
Hi TSLF,

We got an answer. The dropplets do act like pixels and yes it is due to the fact that those water dropplets that all reflect red, are at 42 degrees of the viewer and the light source.

I think it is possible to see a rainbow with only a curtain of water dropplets, see a hose pipe. Did you mean a solid sheet of water? i'm not sure, that's a good question. *edit: If it's a sheet of water with a clean surface it will I think. I've seen little mini rainbows produced by the surface water, I think.

Do moleules act like prisms? or does light refract through mollecules or atoms? Or does it have to be mollecules or atoms suspended in a flat surface? Why is this?

89. Originally Posted by Strange
Originally Posted by question for you
Originally Posted by SpeedFreek
Each time a wave of light interacts with the atoms in the medium, its direction is changed slightly.
But what rules govern the amount that a photons direction changes?
QED: Feynman video. Or do a PhD in physics.

Originally Posted by question for you
No offence fellas... but all this is an analogy of is something turning. I know what turning means. I know what a kink is or a change in direction. I want to know how this physically happens in refraction.
This is the (simpler) classical description. Wavefront hits the boundary at an angle. The change in speed causes it to turn (for obvious physical reasons: see marching band, tank, ruler, stick analogies). Different frequencies slow by different amounts and so turn by different amounts.

Why does that happen?
QED: Feynman video. Or do a PhD in physics.
You don't need an PhD in Physics for that :P most of it is explainable by classical scattering. even the polarization. Only the more complicated optical non-linear phenomen require at least an MsC in physics.

90. Originally Posted by question for you
Do moleules act like prisms? or does light refract through mollecules or atoms? Or does it have to be mollecules or atoms suspended in a flat surface? Why is this?
No, molecules do not act as prisms. the reason why prisms work the way they do is that speed of light is different in non vacuum. This makes different colours propagate at different speeds. Therefore there is a breaking of colour. Molecules don't have this, only certain repetitive molecular constructions like for instance crystals have this, and other, properties.
Also, some surfaces etc can do this. But a mirror generally doesn't. That is why telescopes use mirrors mostly.

91. Originally Posted by Kerling
The reason why prisms work the way they do is that speed of light is different in non vacuum. This makes different colours propagate at different speeds. Therefore there is a breaking of colour. Molecules don't have this, only certain repetitive molecular constructions like for instance crystals have this, and other, properties.
Also, some surfaces etc can do this. But a mirror generally doesn't. That is why telescopes use mirrors mostly.
Thanks for joining in kerling.

Would you know how to explain the fact that red light appears at 42 degrees, blue at 40.89 (I think it was) and the rest in the middle. Why are those frequencies concentrated at different angles?

92. I can, but not as good as Wikipedia:
Dispersion (optics) - Wikipedia, the free encyclopedia

93. Would you know how to explain the fact that red light appears at 42 degrees, blue at 40.89 (I think it was) and the rest in the middle. Why are those frequencies concentrated at different angles?
It's a direct consequence of Snell's law :

wherein the n are the refractive indices. The important point here is that the refractive index of a material is a function of the wavelength - therefore, since different colours correspond to different wavelengths, their deflection angles differ. This is why a beam of white light, when transversing a prism, is split into rainbow colours, since each colour is deflected at a different angle.

94. Originally Posted by Markus Hanke
The important point here is that the refractive index of a material is a function of the wavelength - therefore, since different colours correspond to different wavelengths, their deflection angles differ. This is why a beam of white light, when transversing a prism, is split into rainbow colours, since each colour is deflected at a different angle.
Cheers Markus!

A function of the wavelength! This is the function I want to understand. I'll check kerlings wiki link.

95. Originally Posted by question for you
A function of the wavelength! This is the function I want to understand. I'll check kerlings wiki link.
Hey! I said that 60 posts back. Oh well, never mind...

96. Originally Posted by Strange
Originally Posted by question for you
A function of the wavelength! This is the function I want to understand. I'll check kerlings wiki link.
Hey! I said that 60 posts back. Oh well, never mind...
With all respect Strange, I dont think post 34 explains it entirely:

Originally Posted by Strange
What is it about a surface that only reflects a certain part of the visible spectrum and absorbs the rest?
Two reasons (that I know of). The electrons in the atoms of the material absorb some frequencies and not others. The surface structure causes diffraction effects so that certain frequencies are cancelled and others reinforced. The latter is how many animals (butterflies, for example) create their bright colours.
In fact, Markus describes the defraction as a function of the wave length... you describe how the atoms in the surface structure cause diffraction effects which act on certain frequencies but no others.

I still don't understand what is going on with the wave length or with the atoms in the surface... or why light reflects at the angles it does.

97. Originally Posted by Strange
Originally Posted by question for you
A function of the wavelength! This is the function I want to understand. I'll check kerlings wiki link.
Hey! I said that 60 posts back. Oh well, never mind...
No you didn't... you said it was a function of the atoms in the surface of the material.

98. Originally Posted by question for you
Originally Posted by Strange
Originally Posted by question for you
A function of the wavelength! This is the function I want to understand. I'll check kerlings wiki link.
Hey! I said that 60 posts back. Oh well, never mind...
With all respect Strange, I dont think post 34 explains it entirely:
That is something else. I was just pointing out that several people had already said that the refractive index and therefore the angle the light is turned depends on frequency. But it doesn't matter.

In fact, Markus describes the defraction as a function of the wave length... you describe how the atoms in the surface structure cause diffraction effects which act on certain frequencies but no others.
Markus is talking about refraction (the original topic: rainbows, etc).

You then went on to ask about coloured surfaces, which is a completely different thing. I pointed out that one mechanism for surface colour is diffraction caused by textures on the surface. The more common reason is selective absorption of some frequencies.

I still don't understand what is going on with the wave length or with the atoms in the surface... or why light reflects at the angles it does.

For reflection:

Classical answer: waves bounce off surfaces at the same angle as anything else. A ping-pong ball will "reflect" off a solid surface at the same angle it hits it.

Quantum answer: in QED you have to sum all possible results of the photon interacting with an electron based on their probabilities. It turns out that they all cancel out except the one corresponding to the classical model.

The same is true for refraction.

Classical: As a wave enters the material at an angle, one end will slow down before the other and it will rotate (just like a stick, tank, marching band).

QED: Sum all possible interactions of the photons with the electron based on their probability and you end up with the same answer as the classical model.

99. Complicated indeed.

I wanna see a computer animation of photon atom interaction. How hard can it be?

100. Well, Feynman, in the recommended video lectures, does a series of drawings on the white board to demonstrate what happens. Does that count?

101. Originally Posted by Strange
Well, Feynman, in the recommended video lectures, does a series of drawings on the white board to demonstrate what happens. Does that count?
Surely somebody has done better since then? feyman was a physicist not an artist!

The feyman video is in about 8 parts if I remember rightly and i couldn't find them all on youtube.

If this is sound science then I know there will be illustrated representations of the workings that are either known or suspected... would be fascinating. Surely scientists use high power cameras? Are the videos accessible?

Page 1 of 2 12 Last
 Bookmarks
##### Bookmarks
 Posting Permissions
 You may not post new threads You may not post replies You may not post attachments You may not edit your posts   BB code is On Smilies are On [IMG] code is On [VIDEO] code is On HTML code is Off Trackbacks are Off Pingbacks are Off Refbacks are On Terms of Use Agreement