Difference between revisions of "Photon"

From Conservapedia
Jump to: navigation, search
m (Reverted edits by EDmongPOOR (Talk) to last version by Ed Poor)
(Simplify jargon driven article)
Line 1: Line 1:
{{jargon}}
+
A '''photon''' is a particle of light.  
A '''photon'''  
+
* is a [[fundamental particle]] belonging to a group of particles called the ''[[bosons]]'', which, according to the [[quantum field theory]], have [[integer spins]].
+
* Photons mediate the [[electro-magnetic force]], which includes both [[magnetism]] and [[electricity]].  
+
  
When we "see", our eyes are receiving streams of photons reflected from the objects around us.
+
In [[classical physics]] light is considered to be a wave. One of the proofs for this is that light experiences [[interference]] and [[diffraction]], which would not be displayed if light were a classical particle. Furthermore, [[James Clerk Maxwell]] theoretical prediction of electromagnetic waves, together with [[Heinrich Hertz]] experiments led to conclude that light was an electromagnetic wave.
  
In [[classical physics]] there was a disagreement about the fundamental nature of [[light]] - whether it was a [[particle]] or a [[wave]], as it seemed to exhibit the properties of both. The accepted explanation now is that it is a particle, and that its wave-like properties arise from its lack of [[mass]] (so that it can distribute [[force]]s over long distances) and from the following [[interference]] phenomenon typical to all [[quantum particles]].
+
However, a phenomenon called the [[photoelectric effect]] led to a different conclusion. The photoelectric effect consist on a metal ejecting electrons when a beam of light insides upon it. This by itself is in no contradiction to the wave theory of light, but certain peculiarities of it were. For example, no electrons were emitted unless the frequency of light was greater than a threshold frequency, regardless of how intense the light beam was. Also, the energy of the emitted electrons was dependent only on the light frequency, not in its intensity. Since the energy of a wave depends on its amplitude, which in turn is related to its intensity, this was in contradiction with the wave theory of light.  
  
In [[quantum mechanics]], one can no longer say for sure what the outcome of an experiment will be.{{fact}} The only meaningful question is what the [[probability]] is that the experiment will produce a particular result. These probabilities are [[absolute squares]] of [[complex numbers]] called ''[[amplitudes]]'' associated to the possible outcomes of an experiment.
+
Albert Einstein solved this problem arguing that light is really a particle, which was called a photon, each of which carry an energy given by h*f, where h is the [[Planck constant]] and f is the frequency of the light. More intense light involves more photon, but the energy of each photon individually depends only on its frequency. This explained why there is a threshold frequency before a metal emits electrons: A single photon must be energetic enough to knock out an electron, and so increasing the intensity (sending more photons) will not solve the problem. Only increasing the frequency (increasing the energy per photon) will do.
 +
 
 +
In standard interpretations of quantum mechanics, the light behaves both as a wave and as a particle. The existence of photons is now well accepted by the physics community, and its implication has gone well beyond the photoelectric effect.
 +
 
 +
Photons are [[bosons]], that is, particles that have integer [[spin]]. In [[quantum field theory]], photons are the mediators of the [[electromagnetic force]].
  
Now in [[classical physics]], if the outcome of an experiment could happen in 2 ways, with probabilities A and B, we would expect that the probability of this outcome would be A+B. However, in quantum mechanics, instead of adding the probabilities (that is, adding the squares of the amplitudes), we add the amplitudes first, and then square this to obtain the probability. These means that the amplitudes associated to the two possible outcomes can constructively or destructively interfere with each other, which gives rise to the wave-like behavior observed in quantum mechanics.
 
  
 
==See also==
 
==See also==

Revision as of 03:07, 5 September 2011

A photon is a particle of light.

In classical physics light is considered to be a wave. One of the proofs for this is that light experiences interference and diffraction, which would not be displayed if light were a classical particle. Furthermore, James Clerk Maxwell theoretical prediction of electromagnetic waves, together with Heinrich Hertz experiments led to conclude that light was an electromagnetic wave.

However, a phenomenon called the photoelectric effect led to a different conclusion. The photoelectric effect consist on a metal ejecting electrons when a beam of light insides upon it. This by itself is in no contradiction to the wave theory of light, but certain peculiarities of it were. For example, no electrons were emitted unless the frequency of light was greater than a threshold frequency, regardless of how intense the light beam was. Also, the energy of the emitted electrons was dependent only on the light frequency, not in its intensity. Since the energy of a wave depends on its amplitude, which in turn is related to its intensity, this was in contradiction with the wave theory of light.

Albert Einstein solved this problem arguing that light is really a particle, which was called a photon, each of which carry an energy given by h*f, where h is the Planck constant and f is the frequency of the light. More intense light involves more photon, but the energy of each photon individually depends only on its frequency. This explained why there is a threshold frequency before a metal emits electrons: A single photon must be energetic enough to knock out an electron, and so increasing the intensity (sending more photons) will not solve the problem. Only increasing the frequency (increasing the energy per photon) will do.

In standard interpretations of quantum mechanics, the light behaves both as a wave and as a particle. The existence of photons is now well accepted by the physics community, and its implication has gone well beyond the photoelectric effect.

Photons are bosons, that is, particles that have integer spin. In quantum field theory, photons are the mediators of the electromagnetic force.


See also