What happens to a photon?
372933
A photon will keep going until it gets absorbed.  By the essense of your question, I am guessing that you are thinking of photons in terms of a solid particle.  True, it can be thought of as a particle, that is part of wave-particle duality.  But the truth is, we cannot really understand wave-particle duality in an intuitive way.  The mathematics are well understood, but as humans we cannot really grasp, it does not make sense to our everyday experiences.  Don't think of it as a particle disappearing.  A photon is merely a means of transmitting energy.\n\nMaybe this will help:  An atom is in an energized state with an electron in a higher orbital.  The electron drops to the ground state and a photon is emitted.  That photon travels either 10 nanometers or one light year (doesn't matter) until it interacts with another atom of the same kind.  That second atom absorbs the photon and an electron gets excited to the same state as the electron in the orginal atom.  So in this sense a photon is just a means of transferring energy.  No matter is created or destroyed.
528620
So, I don't know if that last word was supposed to be photoelectrons or photons.  So, I'll do both.\n\nIf there is an energy gap, and the energy of the photon is sufficient to promote an electron from one of the energy states in the fermi sea to an allowed energy state above the gap, the electron can be promoted to a state above the energy gap, and a hole will be produced in the state it came from.  Because there are lots of vacant energy states above the energy gap, the electron is in the conduction band, and can move around lots...  That's how you get photoelectrons.\n\nNow, photons would be produced when those photoelectrons recombine with holes.  The photoelectron has some finite lifetime, after which it will recombine with a hole (probably not the same one).  This will result in the electon losing energy in the form of a photon.
1050469
A photon cant be split in half, but it is possible to perform single photon interference experiments, whereby using a double slit apparatus one creates a situation where a photon if acting as a particle would pass through one slit or the other and produce an effect on something behind the slits, such as a photographic plate.  When a double slit is used, and if no attempt is made to determine which slit the photon passes through, then the wave properties take over, and a different interference pattern results, according to the rules of diffraction, or Huygen's principle.  Effectively, sending half the photon through one slit and half through the other.  So in effect, an object can be in two places at one time, as long as nobody is looking.
80793
According to reletivity, the transformed velocity is zero.\n\nPhotons will see each other at rest,\n\nAlso it is interesting to know that it takes no time for photones to travel all the world if ask them.
66479
No Way Man!  Photon-photon scattering?  Highly dubious.  Photons don't have charge. They don't self-interact, that's why the electro-weak theory works so well... right?\n\nResponse to Dr. Bob's response:\n\nI agree that this process occurs (although a photon that decays into a e+e- pair has to be close to another mass so momentum can be transfered; isolated photons cant decay into e+e-).  But in such a case, would you really say that "one light ray has bounced off another?" I'd say that it was "bouncing" off the electron/positron pairs.  Just semantics I suppose.
721710
Short Answer:\n\nThe photon is generally accepted to be massless and experiments show that its mass is consistent with zero.\n\nLong Answer:\n\nLight is composed of photons so we could ask if the photon has mass.  The answer is then definitely "no": The photon is a massless particle.  According to theory it has energy and momentum but no mass and this is confirmed by experiment to within strict limits.  Even before it was known that light is composed of photons it was known that light carries momentum and will exert a pressure on a surface.  This is not evidence that it has mass since momentum can exist without mass.\n\nSometimes people like to say that the photon does have mass because a photon has energy E = hf where h is Planck's constant and f is the frequency of the photon.  Energy, they say, is equivalent to mass according to Einstein's famous formula E = mc2.  They also say that a photon has momentum and momentum is related to mass p = mv.  What they are talking about is "relativistic mass", an outdated concept which is best avoided Relativistic mass is a measure of the energy E of a particle which changes with velocity.  By convention relativistic mass is not usually called the mass of a particle in contemporary physics so it is wrong to say the photon has mass in this way.  But you can say that the photon has relativistic mass if you really want to.  In modern terminology the mass of an object is its invariant mass which is zero for a photon.\n\nIf we now return to the question "Does light have mass?" this can be taken to mean different things if the light is moving freely or trapped in a container.  The definition of the invariant mass of an object is m = sqrt{E2/c4 - p2/c2}.  By this definition a beam of light, is massless like the photons it is composed of.  However, if light is trapped in a box with perfect mirrors so the photons are continually reflected back and forth in the box, then the total momentum is zero in the box's frame of reference but the energy is not.  Therefore the light adds a small contribution to the mass of the box.  This could be measured - in principle at least - either by an increase in inertia when the box is slowly accelerated or by an increase in its gravitational pull.  You might say that the light in the box has mass but it would be more correct to say that the light contributes to the total mass of the box of light.  You should not use this to justify the statement that light has mass in general.\n\nIt might be thought that it would be better to regard the relativistic mass as the actual mass of photons and light, instead of invariant mass.  We could then consistently talk about the light having mass independently of whether or not it is contained.  If relativistic mass is used for all objects then mass is conserved and the mass of an object is the sum of the masses of its part.  However, modern usage defines mass as the invariant mass of an object mainly because the invariant mass is more useful when doing any kind of calculation.  In this case mass is not conserved and the mass of an object is not the sum of the masses of its parts.  For example the mass of a box of light is more than the mass of the box and the sum of the masses of the photons (the latter being zero).  Relativistic mass is equivalent to energy so it is a redundant concept.  In the modern view mass is not equivalent to energy.  It is just that part of the energy of a body which is not kinetic energy.  Mass is independent of velocity whereas energy is not.\n\nLet's try to phrase this another way.  What is the meaning of the equation E=mc2?  You can interpret it to mean that energy is the same thing as mass except for a conversion factor equal to the square of the speed of light.  Then wherever there is mass there is energy and wherever there is energy there is mass.  In that case photons have mass but we call it relativistic mass.  Another way to use Einstein's equati
659419
Basically photons (or light) are the particles that is exchanged in communicating the electromagnetic force. To understand the essence of electric charge then you must understand light, or EM fields. This is independent of the atom.
522376
I believe it DEPENDS on the Frequency of that photon.\nWHITE lite comes into a prism (water droplets) and the\nindividual photos are BENT (refracted) various amounts\ndue to their frequency... thus we get to see the spectrum\n... rainbow... \nSo, yes, a photon going from one medium into another\nwould alter it's path a little at the juncture, \naccording to its frequency...  no "references", \njust my  off-the-cuff reply.  good luck.
875956
The energy of a photon is proportional to its frequency, the constant of proportionality being called Planck's constant who discovered this relation.\n\nE = h * Frequency\n\nIf you know the frequency (or wavelength) of the light you can calculate the corresponding energy.\n\nWhen an electron jumps from an excited state back to its ground state it will emit energy.  If the frequency is in the right range we will see that as light.
194230
Between the electron and photon, photons will be smaller and lighter. But to counter it, there are actually even smaller things called quarks found in the electron and proton. These are REALLY small and each electron contains THREE of them, so u can imagine how small there are.
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The photon has energy. And energy can be converted into mass. Remember \n\nE^2=(m^2)( c^4) + (p^2) (c^2)\n\n----------\n\nI would agree with cedykeman1 that it does seem somewhat controversial to suggest that the photon is unstable. However, its energy can still probably be converted to matter, although the chance of getting those 3 exact particles seems a bit far-fetched (probably their antiparticles have to be produced as well, and various conservation laws followed carefully).\n\n--------\nI do not know what to say about goring, except to smile.
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I like your question and hope it is one that you yourself thought up rather than someone handing you and expecting some pat answer back. \n\nThe difficulty we have in answering it is the word "entity." In our ordinary world, a door is an entity so is a kitten. When a kitten jumps through a door, there is no chance that the kitten will go through the door and come out as a rain of kittens (diffracting) with a solid seeming kitten in the center and some ghostly kittens further out. And yet, photons do that.\n\nWe allow photons to travel at the speed of light in a vacuum. Nothing else is allowed to do that. Hard to talk of entity with that exception given to it. \n\nI am not sure, even though I teach about photons, that we can talk very concretely about them as entities. Mathematical conveniences? Convenient? Had to learn a whole new way of doing math but yes, I guess. Information carriers might be an interesting way of putting it, too, in a Feinnman sort of way.\n\nNow I will be thinking about this all day. Good question.
30961
Since the spectra of a given element shows a discrete number of color bands (rather than a continuous specturm), and since the color of light relates to its energy, and since photons are released by the relaxation of electrons from a higher to a lower energy state, it follows that the gaps between energy levels are distinct and finite.  This means that the energy levels are quantized.
724946
it absorbs light energy aka the photons and bounces them around and releases electrons
102101
If you want to look at it on the atomic level,\nyou can think of light as a photon (a packet of energy).\nThe photons can be absorbed by the electrons around the atom which will excite them into a higher energy state.  When the electron falls back down to the ground state, it gives off a photon with a specific amount of energy.\n\nhttp://www.amazingrust.com/New/beta/Experiments/background_knowledge/Spectroscopy.html
1107614
No.. and yet... Here we go into quantum physics. One of the interesting things about your question is that it really depends on how you look at it. The observer actually affects what an electron is observed to be: basically- if you look for the electron to behave as a particle- it will. You will find that it has mass, and a velocity, etc. If you look for it to behave as a wave- you will find that as well. :) So, when it is a wave, it does have an innate frequency. Actually, it has one of several 'quantized' energy levels. If an electron gets excited (yes, physicists really use that term) it jumps up to a higher energy level. If it finds a way to release that energy (electromagnetic radiation, or light) it will return to is normal state. This explains many things in the real world, such as flourescent colors, photoluminesence, etc. Anyway- thats the quick version. For more depth, grab a modern physics book. :)
247190
The patterns are the same.  It doesn't matter if you send the photons through one at a time or many at once.