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Old 09-07-2008, 06:40 AM #1
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Default Photons

Just some qustions on photons

Do photons have a mass? I heard they did as this is the reason they seperate thorugh difraction.

Do photons of a different wavelength have a different size, mass, density etc.

How big is a photon?

Can you see them under a micsroscope?


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Old 09-07-2008, 07:09 AM #2
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Default Re: Photons

Mass = 0 (resting)
Different Sizes: No only different energies
Size of a photon: point particle (size has no meaning)
Can they be seen? Yes, indirectly. They are seen as cosmic rays down to radio by their influence on matter (absorption and transfer of energy, or re-release due to electromagnetic transfer)

A photon is not an easy thing to describe using classical physics. Quantum mechanics must be employed to fully realize the dual nature of the photon (study deBroglie, Schrodinger, Heisenberg, and even Einstein (particle nature, photoelectric effect)).
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Old 09-07-2008, 07:16 AM #3
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Default Re: Photons

different energies?
so do low wavelengths have higher energies as they can carry more information, eg, blu-ray to an IR diode...
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Old 09-07-2008, 07:23 AM #4
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Default Re: Photons

Short wavelengths have higher energy and are thus at the blue end of the visible spectrum whereas red wavelengths have lower energy.

To calculate the energy of a photon you can use the equation:

E=hc/[ch955] where E is energy, h is Plancks constant, c is the speed of light and [ch955] is the wavelength.
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Old 09-07-2008, 11:14 AM #5
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Default Re: Photons

If your talking about information storage on disks, blu-ray holds more because it has a smaller focal point, meaning that you can fit more 'dots' onto one disk, IR has a larger focal point meaning less 'dots' on one disk. That is why Blu-Ray holds more than CD or DVD.
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Old 09-07-2008, 03:11 PM #6
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Default Re: Photons

Quote:
Can you see them under a micsroscope?
Yes sure you can see them as long as they're in the visible spectrum, and you don't need a microscope Photons reflected off of objects is what you always see.I read somewhere that you have a 50% chance of seeing a single photon in complete darkness if it hits you in the eye. :P Of course you can't see a photon passing by , as it would mean that other photons have to bounce off of that photon and hit you in the eye.....not to mention that it's travelling at the speed of light. So whatever microscope you have , seeing it in the way that you thought about it is not possible.
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Old 09-07-2008, 05:41 PM #7
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Default Re: Photons

When a photon hits the eye (the front) it has the choice of reflecting and refracting. That's your 50%. Actually it does both, as quantum theory dictates, but when it is observed, the state collapses to where it is either here or there. (see comic

Other facts:
Photons have no mass, and hence always travel at the speed of light in vacuum. When they appear to travel slower than the speed of light (eg in a medium), the photon is actually absorbed and re-emitted billions of times (requires quantum theory too to fully describe)

Mirrors are actually diffuse at the atomic level (there is no such thing as a flat surface at the atomic level, as there are no atoms with flat sides). The light actually emits in all directions at once (called a wavefront, akin to a wave created by dropping a stone in a pond), however all light that travels in one particular direction (the reflection angle) undergoes constructive interference, while light in all other directions experience destructive interference.

CDs, DVDs, etc. have grooves which are separated from each other only a few wavelengths in length, and this creates a strange effect. Photons that hit a groove get lost (for simplicity), and photons that hit the flat space between the grooves are emitted in all directions as a wavefront. The alternating present and absent wavefronts create a 'mirror' where multiple angles undergo constructive interference, and these angles depend on the wavelength too. Hence the rainbows.


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Old 09-08-2008, 04:34 PM #8
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Default Re: Photons

Lol at the comic ;D
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Old 10-24-2008, 10:24 AM #9
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Default Re: Photons

well, i have some new thoughts.
what realy happens when two coherent lights are crossed such as two laser beams?
in the pictures numbered;
#1 - Will the photons pass each other with no effect
#2 - Will some pass with no effect while some absorb or pass through another cuasing yellow in this case + reducing performance.
#3 - Will some pass each other and some collide being destroyed + reducing performance.
#4 - And, some pass, while some are cought and dragged into the other beam. Such as when you get two hoses and make the stream hit...
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Old 10-24-2008, 02:03 PM #10
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Default Re: Photons

They'll pass each other without any loss in power or canceling each other out, and definetly won't change wavelength and become yellow. :

The yellow you see by combining a red and a green beam is just an artifact of your optical system.It is still green and red, not ~580nm.The eye gets hit with green and red and the brain interprets it as yellow.
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Old 11-01-2008, 11:11 PM #11
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Default Re: Photons

I grew up a lot, way back on the day I learned that light didn't really mix into a different wavelength. *It's all just a trick our minds play on us.
It's so obvious now, but as a child, it really changed the way I saw the world.
So much of the man made light we surround ourselves with is just 3 wavelengths. *That's even far more true now than it was back when I learned that.

(maybe someone here can relate to that... most people can't )
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Old 11-06-2008, 03:49 AM #12
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Default Re: Photons

Quote:
Originally Posted by caleb
Just some qustions on photons

Do photons have a mass? I heard they did as this is the reason they seperate thorugh difraction.

Do photons of a different wavelength have a different size, mass, density etc.

How big is a photon?

Can you see them under a micsroscope?


i think it depends on the &quot;mass&quot; you are talking about... since mass can be described in terms of energy.... light has momentum, but it can't be explained as p=mv that doesnt work anymore. i think it has something to do with the fact that momentum and energy are pretty much on the same page according to Einstein.... this is actually really hard to explain, specially because i dont know much about the subject, i just remember my physics teacher saying something about the spin of an atom or something like that, possibly what happens when light passes through a medium, not vacuum. &quot;the photon is actually absorbed and re-emitted billions of times&quot;(quote of zom-b) maybe possibly transferring some of that energy into the particles...???... just a thought.
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