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# Tag Archives: photon

## Seeing and photons

If we see an object because of light from the source hitting the surface of the object make its electrons to excite to higher orbits and coming back to same orbit emitting a photon which strikes our eyes, then according to this, at one INSTANT of TIME, an excited electron can emit only one photon and similarly if the object contained (for example) ten electrons on its surface, only ten photons can come form that object at that instant of time and all those photons will have 3 degree of freedom to move in any direction.IF this is the case, we could not see a complete object at a given instant of time as all the photons emitted from that object woudn’t have striken to our eyes and similarly, if 3 people are watching the same object, at a given instant of time, each person would have seen a part of that object as one electron emits only one photon at that instant of time…. but this is not the case in real world….how is it?

We are not seeing an object not just because of a single of photons or not even just a handful of them.

For example, if we have a 100W bulb emitting light of wavelength 6000 angstrom, the total energy emitted per second is 100 J.

The energy of a single photon is

$h\nu&space;=\frac{hc}{\lambda&space;}=\frac{6.6&space;\times&space;10^{-34}\times&space;3\times&space;10^{8}}{6000\times&space;10^{-10}}=&space;3.3&space;\times&space;10^{-19}&space;J$

Which means that each joule of light energy is caused bu 10^18 photons.

A single photon cannot cause the sensation of vision. Remember, we cannot see in dim light. In order to see there must be a minimum required intensity (the number of photons falling per unit area per second multiplied by the energy of a single photon)

It was found that the emission of only 90 photons was required in order to elicit visual experience. However, only 45 of these actually entered the retina, due to absorption by the optic media. Furthermore, 80% of these did not reach the fovea.

## Photon and Antiphoton

I heard that photon is its own antiparticle. If so, what is the different between these two photons

Photons also have their antiparticles, but antiphotons are photons themselves.

http://arxiv.org/abs/1009.5119

http://van.physics.illinois.edu/qa/listing.php?id=1153

http://www-3.unipv.it/fis/tamq/Anti-photon.pdf

## Ron writes on Light and Relativity

Let me start by saying I am NOT a physicist.  That much should be painfully clear soon enough.  Please bear with me as I am not certain I have the language and in depth knowledge to explain myself adequately.

A few years ago I began experiencing parallels between the world of human behavior and physics.  At the time it seemed simple enough.  That is until I started teaching myself physics.  But at its core it seemed to make sense, the rules of life recycle themselves in different forms.  Out of simple ideas comes complexity.  Newton’s laws, thermodynamics… pascals principle, snells law, red and blue shift, wave particle duality and on and on… all seem to have their parallels in human behavior and on the surface seem to follow the same mathematical equations. Then I ran into the most famous of physics equations E=MC^2.  It makes sense in human behavior.  The energy (work) we can get out of an individual is relative to that individuals’ mass.  The more matter we attach to the individual, knowledge, life experience etc (therefore increasing their mass) the more we can get out of them in the form of energy… but then the problem of the speed of light squared.  The only known constant (light speed) is a problem in human behavior.  At least to this point I know of no known behavioral constant.

I juggled the idea of it being a relative constant.  Constant for the individual but relative as it would differ for everyone.  The speed of cognition, or thought speed, would remain the same in potential throughout life of a given individual.  Or that it was just a theoretical potential that humanity had yet to obtain.  I even juggled the idea of it being a collective ability, but all of these options cause problems with the original equation.  This has forced me to contemplate the nature of light and left me with questions I simply lack the understanding of physics to answer.

Is the speed of light truly constant or is it only constant as it relates to the big picture?  As in: our perception of time as it relates to all time that has ever existed would appear as a single point in time.  The older we get the more time seems to “fly by”  if we as humans could continue to live for 13 billion years would the perception of an hour become so perceptively small that we wouldn’t even know it has passed?   Is it therefore possible we can only understand and therefore measure the speed of light at a specific point in time, even if we try to come back and remeasure and compare the speed of light now with the speed of light fifty years from now the difference between the two would be imperceptivity small as a result of the displacement in time as it relates to the whole of time?

If the four dimensionality of time/space is linked shouldn’t time expand as space expands? And vice versa… if the speed of light is to remain constant as measured under such conditions isn’t light actually slowing down/speeding up over time as it relates to the whole of existing time/space?  It’s a distance displacement problem…. If points A and B are actually farther apart but light travels the same distance in the same time the “speed” may seem constant but time has actually expanded to give the light more “time” to cover that distance.  The speed of light would therefore be constant as a relation to perception and not as it relates to physical principles. Like the fact that the perception of time changes as we get older even though the actual measure of time remains the same.

How can light exist forever?  At the speed of light we theoretically freeze time for that photon but that would also require an infinite amount of energy to obtain and maintain. So even a subatomic particle with a lifespan of a nanosecond would appear to exist for all eternity but in actuality would still only exist for a nanosecond.  Because quite simply…it can’t have infinite energy and if it can I don’t understand how.  Thermodynamics: no system is a perfect system and will experience energy loss, Newton: equal and opposite reaction, if something begins it has to end to balance the equation.

Is it therefore possible that light is born of the fourth dimension… we experience it in the dimensionality of space as long as it loses its energy to the three dimensions.  A photon folds and pushes its way through space/time  The initial energy of the photon is high and generates bigger leading waves which resist the photon holding it from passing the “speed of light” as the energy dissipates/photon begins to die those folds restricts the photon less allowing it to maintain the speed of light.  We experience light because of its “ripples” in three-dimensions light dissipates as the waves of space become less folded in front of the photon.  But this would mean the photon eventually loses enough energy that it can no longer be perceived in the third dimension….  So what happens to it??  Imagine : A man running through a corn field has to exert the energy to push the stalks aside but  over time if the corn stalks are slowly spaced out even as he loses energy he can maintain his pace, because there is less impeding his path.  Our perception of light would be like being in a helicopter looking down on the field.  In the begging the field is densely packed with cornstalks and they slowly spread out until there is none.  We only know the man is there while he is running through the corn because he pushes the stalks aside and we see that movement but once there are no stalks or he lacks the energy to continue running we no longer have a way of measuring his presence.

That brings me for some reason to a theory of Dark matter.  Why?  Well what happens to photons that no longer move with enough force to be visible.  Like that guy running from a cornfield into an empty field.  How would we know he is still there?  If it was an infinite number of guys all stopping in that empty field we would know they are there by the depression their weight leaves in the field.  Or more accurately by the stones in the field rolling towards a depression we cant actually see.  The thought: An infinite number of “massless” (or perceived mass less) subatomic particles would still have infinite mass.  Infinite mass would supply more then enough gravitational pull even spread out over infinite distance to cause the continued and speeding expansion of space as more and more visible photons “die” contributing its “dark masslessness”.  Any dark matter existing within the universe would act as force… a moving invisible mass existing only on the 4th dimension pushing upon any objects in its way.  But because energy propagated internally expanding outward in all dimensions would compound on the outside as those energy’s converge.

I hope you followed those questions.  I don’t know what these ideas would do to theoretical physics but it would allow for the relativity of cognitive speed between individuals and reopen the door to “what the hell is dark matter in relation to human behavior” but that’s something different all together.

## Wave particle duality

Let n and m denote the number of photons emitted by a red and blue bulb respectively of equal power in a given time.Is n=m?

No

The energy of a photon is hν

where ν is the frequency.

Power = energy/time

==> nhν1 = mhν2

==> nν1 = mν2

clearly n not equal to m

## A question on Quantum Entanglement

I have read a lot about quantum mechanics but have a query.
using an entangled photon for this question.

If you can’t measure an entangled photon without affecting it’s entanglement then how do we know it was even entangled to start with and not just always a certain “spin”, either up or down. How can we say for sure that it is both at the same time (entangled) with never observing or measuring this?

[LM posted this]

Response

As of now, We can only give you some links for further reference. Learnt visitors can respond with  an anwer.

## Electricfield, Magnetic Field and Photon

We know that photon has no charge. Then where from it gets electric and magnetic field in light?

Electric and magnetic fields are not produced by the photon; it is massless too.

But, photon is created by time varying electric and magnetic fields, usually produced by accelerated charges.

As you might have already learnt, a charge at rest produces an electric field around it. A moving charge (current) produces a magnetic field around it as well as magnetic field. A varying current produces a varying magnetic field and hence an induce emf or current. An accelerated charge produces a time varying electric and magnetic fields.

Thus under suitable situations, the electric and magnetic fields can reinforce each other and propagate out as pure electromagnetic form of energy and such a packet of energy is called photon.

## A Quantum Physics based Question : Can Anyone answer this?

Can anyone answer this Quantum Physics Based question posted by Ian Mc Tavish?

“I would very much like someone who has access to the necessary equipment to perform the following suggested experiment or let me know if this has already been done and what the results were.

I should apologise in advance for my lack of proper scientific terminology as I have had no formal physics training other than the thought experiments I have posed to myself and reading a few books on physics and astronomy and articles online.

Firstly, I understand that when light is shone through two slits it causes a pattern of light and dark on the screen behind thus suggesting that light is a wave.

Secondly,  when the rate at which the light is emitted is slowed down so it can only be a photon(?) at a time there is still an interference pattern.  Suggesting the photon goes through both slits at the same time and somehow interferes with itself….giving birth to quantum physics and a whole lot of outlandish theories (I have an even more “outlandish” theory myself)

Finally, it gets even stranger, when any kind of device is put in place to measure or count which slit each light particle is going through, the pattern changes to diffuse. At last being what you would expect to see from individual particles.

The strange part is, of course is how can just the act of observing cause a diffuse pattern. If the measuring device is switched off it goes back to bands of light and dark.

I hope I have this reasonably correct so far ?

SO…..what would happen if the device that measured which slit photons went through was powered by some kind of voltaic cell that was placed where the light bands are.

That is to say only when the light was making the banded pattern would the power be sufficient to switch on the device measuring which slit the light particles went through….which will then make the pattern diffuse….which will switch off the machine…….which will then make the pattern banded……which will switch on the machine…..ad infinitum.

This seems to cause the same paradox as Schroedinger’s Cat but a lot easier to test and more animal friendly…..a bit of Hawkins style humour there…haha.

If this is the first time someone has suggested this and it does prove useful in any way I would very much like to make my parents proud and have this referred to as the “McTavish Twist”.   The first part being my surname and “twist” because I love twists in both science and cocktails !!!  Both are refreshing and alleviate the boredom..

One suggested result is that the measuring device switches on and off at the speed of its slowest component.  If there was nothing slowing down its rate of switching then it would be very interesting to measure the number of times it changes state per second ?  Although I imagine this may take some clever machinery indeed as the resulting figure should be the smallest possible measure of time.  A “universal tick” ?  (maybe we can call it a “McTavish Tick” or am I getting greedy !!).  I imagine this should link mathematically to the maximum speed of light in some way.

Another possible outcome is that the machine will not switch on even though the light level appears sufficient to power it.  This could happen because it is only really at half power…..being half in the diffuse pattern (that is to say half in another state/universe).  It may be interesting to note where the “tipping point” is ?  Does it really work out to be exactly one half or does it lean more towards one state ?  Again this ratio may link mathematically to another well known number.

I imagine the actual results of the experiment will lead as usual to more questions.  I would very much like confirmation of the results so my own thought experiments move on to new questions too.

Thank you sincerely for your attention.”

Experts in the field are requested to respond

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