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### Author Topic: can red light contain more energy than blue?  (Read 12373 times)

#### yor_on

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##### can red light contain more energy than blue?
« on: 03/04/2009 22:56:36 »
This is a question that puzzles me :)

"blue light puts off more energy when looking at the Electromagnetic spectrum as a whole from the right to left (or from highest wavelength and lowest frequency (i.e radio waves) all the way to gamma rays with extremely small wavelengths and high frequencies) the energy increases. so the energy of radio waves is much smaller than gamma rays

now to put that to use in the problem of light, we know that red light has a larger wavelength (somewhere around 600-700 nm) and blue light with a smaller wavelength of somewhere around 475 nm thus the frequency (wavelengths per unit time) is larger for blue light

using the equation E=((hc)/wavelength) where E is energy, C is the speed of light (3x10^8 meters/second) h= planks constant of 6.626 x 10^-34 joules x seconds

we find that plugging in a smaller wavelength gives us a higher energy "

So in what way isn't this equivalent to red and blue shift?

I'm not sure of why those two wouldn't describe the same 'energy equivalences/proportions'. the only way I can understand red light to contain more energy per tine unit than a blue light is if you somehow either use more energy to produce that red light and/or somehow connect those lasers in 'series'.

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#### Vern

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##### can red light contain more energy than blue?
« Reply #1 on: 04/04/2009 00:09:12 »
I like to think of light as photons, little bundles of energy-time, each of which has energy as per your equations. You can transfer more power by causing more photons to transfer from place to place, but each individual photon still has the same energy-time.

I don't know of a theoretical limit to the amount of power a single beam of photons can transmit from place to place. Of course, as Einstein noticed, it is the energy-per-photon content and not the power transferred that dislodges electrons from metals.

#### lyner

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##### can red light contain more energy than blue?
« Reply #2 on: 04/04/2009 00:23:42 »
Quote
So in what way isn't this equivalent to red and blue shift?
Is there some suggestion that it isn't? Do you see some sort of conflict with this?
If you regard the Expansion of the Universe as a mechanism which limits the energy which can be transfered between distant points then it seems very reasonable that em energy from distant objects should get less and less, with distance.

#### kenneth

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##### can red light contain more energy than blue?
« Reply #3 on: 04/04/2009 00:57:35 »
I always learned that red light, since it has a longer wavelength, is less resistant to being scattered. Thus this is the reason mankind has chosen red lights to be of utmost importance (i.e. the brake light, ambulance lights, police lights) and is also the reason that the sunrise and sunsets are usually more red tinted, because there is more atmosphere for each light particle to travel through, and in effect what is left after a prolonged stay in the atmosphere, you are left with more red light than anything else because of its longer wavelength.

that being said, I have absolutely no idea if I even came close to answering your question because I am not knowledgeable enough to do so.

BUT can someone also explain to me the green flash? I actually was lucky enough to catch the green flash when I was in California. Why is it the green wavelength that outlasts all others in that instant?

#### yor_on

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##### can red light contain more energy than blue?
« Reply #4 on: 04/04/2009 01:37:19 »
Well, I had a conversation some time ago where I got the impression that red light just as blue could contain a lot of energy per time unit (red laser f. ex:)

Until then I've always assumed that a 'lower wavelength' stretched out per time unit represented a lower energy containment, or fewer photons if you like, but thinking of that red laser made me question if I was correct there? So, how high can you get the energy in a red laser, what kind of work will it be able to do?

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http://mintaka.sdsu.edu/GF/
« Last Edit: 04/04/2009 01:39:14 by yor_on »

#### lightarrow

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##### can red light contain more energy than blue?
« Reply #5 on: 04/04/2009 04:33:36 »
Well, I had a conversation some time ago where I got the impression that red light just as blue could contain a lot of energy per time unit (red laser f. ex:)

Until then I've always assumed that a 'lower wavelength' stretched out per time unit represented a lower energy containment, or fewer photons if you like, but thinking of that red laser made me question if I was correct there? So, how high can you get the energy in a red laser, what kind of work will it be able to do?

Imagine to shoot drops of red paint against a white wall (here the colour red is just to make the visual effect stronger). If all the drops have the same, little volume (or mass, if you prefer), that is the analogue of low-energy photons. Now I ask you this question: if you know every drop's volume, do you have enough information to compute how much red paint will be sent to the wall in 1 minute?
After you have answered this question I explain the rest.

#### yor_on

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##### can red light contain more energy than blue?
« Reply #6 on: 04/04/2009 11:53:53 »
No Lightarrow :) I reckon you will need the 'amount' of them sent per 'time unit' too. But if looking at it as a linear 'causality chain' made from 'photons' I still don't see how the energy per 'hit' can become stronger than blue light, even though the energy per expended 'time unit' may be as strong. Although there may be a connection, if the amount of energy over a given very short time builds up to the same strength? But that's a vauge guess :)

#### Vern

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##### can red light contain more energy than blue?
« Reply #7 on: 04/04/2009 15:38:32 »
I don't remember seeing a suggestion that "energy per hit" could be more for light of longer wavelengths. If "energy per hit" means a single photon. But a thousand photons could deliver more power, (energy-time) than one high energy photon.

This brings to mind a recent discussion about the number of wave cycles that comprise a single photon. Where does the time portion of the energy-time of a single photon come from? Could it possibly be the duration of the wave cycle?

#### lightarrow

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##### can red light contain more energy than blue?
« Reply #8 on: 04/04/2009 16:15:39 »
No Lightarrow :) I reckon you will need the 'amount' of them sent per 'time unit' too. But if looking at it as a linear 'causality chain' made from 'photons' I still don't see how the energy per 'hit' can become stronger than blue light, even though the energy per expended 'time unit' may be as strong. Although there may be a connection, if the amount of energy over a given very short time builds up to the same strength? But that's a vauge guess :)
I almost repeat what Vern has already written: if with 'hit' you mean a single photon detection, then this energy is proportional to the wave's frequency, so a red light will have *less* energy.

But you can send billions of red-light photons at the same time and detect them all in a micro-microsecond and then the energy of this detection will be billions of times greather than that of a single blue light photon detection.

The analogue with the paint drops is that you can also send more drops at once, instead of one at a time.
« Last Edit: 04/04/2009 16:18:24 by lightarrow »

#### lightarrow

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##### can red light contain more energy than blue?
« Reply #9 on: 04/04/2009 16:22:16 »
This brings to mind a recent discussion about the number of wave cycles that comprise a single photon. Where does the time portion of the energy-time of a single photon come from? Could it possibly be the duration of the wave cycle?
Can you explain better?

#### Vern

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##### can red light contain more energy than blue?
« Reply #10 on: 04/04/2009 17:44:09 »
Quote from: lightarrow
Can you explain better?
Can't the wave length of a single photon be found by dividing the frequency by the speed of light? That should give you one wave cycle. Since a quantum is the energy-time of a single photon, and the time portion is linked directly to frequency, it seems the time duration of a quantum needs to be one wave cycle.

Here's a Wiki take on it
A photon is often referred to as a "light quantum". The energy of an electron bound to an atom (at rest) is said to be quantized, which results in the stability of atoms, and of matter in general. But these terms can be a little misleading, because what is quantized is this Planck's constant quantity whose units can be viewed as either energy multiplied by time or momentum multiplied by distance.
« Last Edit: 04/04/2009 17:49:31 by Vern »

#### lightarrow

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##### can red light contain more energy than blue?
« Reply #11 on: 04/04/2009 20:55:28 »
Quote from: lightarrow
Can you explain better?
Can't the wave length of a single photon be found by dividing the frequency by the speed of light? That should give you one wave cycle. Since a quantum is the energy-time of a single photon, and the time portion is linked directly to frequency, it seems the time duration of a quantum needs to be one wave cycle.

Here's a Wiki take on it
A photon is often referred to as a "light quantum". The energy of an electron bound to an atom (at rest) is said to be quantized, which results in the stability of atoms, and of matter in general. But these terms can be a little misleading, because what is quantized is this Planck's constant quantity whose units can be viewed as either energy multiplied by time or momentum multiplied by distance.
In support of your idea I have this little consideration (which I'm sure you already had): the phase φ of a wavefunction is, in the classical limit, S/h where S is the action, so S = hφ; the minimum value of the action, since h is constant, comes for the minimum of the phase φ, which is 2πn where n is the number of cycles; the minimum of n is 1 so if we assume that there can't be a fractionary number of cycles (that is, that n must be an integer) to have an inter-action between two bodies, then we have that the quantization of the action could be interpreted as the fact we must have an integer number of cycles, for an interaction (more precisely, one, at least).
But the fact a single photon could be associated to a single cycle of EM radiation, fights against the fact that the frequency of an EM radiation can be more or less determined (ex. spectral lines more or less sharp) and with the fact that the emission time of an atomic (for example) transition can vary, and a lot. How can you explain these two facts if you assume that a photon is 1 single cycle of EM rad.?

#### Vern

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##### can red light contain more energy than blue?
« Reply #12 on: 04/04/2009 21:10:07 »
That didn't seem a problem to me because I assumed that photons lined up end to end giving the frequency and allowing Heisenberg to be happy So my thinking was that we normally find them in great groups of pulse trains.

So even though we wouldn't normally find them in singlets, I always assumed a single photon could possibly exist, and that it would represent one quantum of energy-time.

#### yor_on

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##### can red light contain more energy than blue?
« Reply #13 on: 05/04/2009 03:05:15 »
But we do have single photons Vern, even though we can't define them as such before they 'hit' whatever they are expected to hit. The problem with any definition we make about them before any 'detection' is that they only can be a 'probability'. So in that motto nothing can be said to be decided before it has happened. If we look at a atomic transition i assume we are discussing events mediated by 'virtual photons'?

And if is so, they don't even seem to 'exist' in our spacetime, only their interactions are measurable, not the 'virtual photons' in themselves, that is, we won't be able to 'detect' them. So how should a definition of a single photon look like? Virtual or 'real'?

#### lightarrow

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##### can red light contain more energy than blue?
« Reply #14 on: 05/04/2009 05:02:17 »
That didn't seem a problem to me because I assumed that photons lined up end to end giving the frequency and allowing Heisenberg to be happy So my thinking was that we normally find them in great groups of pulse trains.

So even though we wouldn't normally find them in singlets, I always assumed a single photon could possibly exist, and that it would represent one quantum of energy-time.
In your model the energy of every photon is given by its frequency only, so it should be totally determined, but actually a single photon's energy is not well determined, and this is shown just from the fact that spectral lines have non-zero width.

In a specific electronic transition of an atom, for example, you can collect the photons emitted, one after the other, and make them go through a prism and then on a detector screen. After billions of photons detected, you can see a line which has a specific width, which depends on the kind of transition, not on the fact that you had one or more photons "lined up".
« Last Edit: 05/04/2009 05:09:01 by lightarrow »

#### Vern

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##### can red light contain more energy than blue?
« Reply #15 on: 05/04/2009 13:44:35 »
And if is so, they don't even seem to 'exist' in our spacetime, only their interactions are measurable, not the 'virtual photons' in themselves, that is, we won't be able to 'detect' them. So how should a definition of a single photon look like? Virtual or 'real'?
I suspect that photons are real electromagnetic potential. I view them as a disturbance that moves through space in a predictable path. The notion of virtual photons came about because some interactions were difficult to explain using real photons that must comply with physical laws.

My feeling is that our explanations are incomplete when we must rely on virtual entities in the explanations.

#### Vern

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##### can red light contain more energy than blue?
« Reply #16 on: 05/04/2009 14:00:50 »
Quote from: lightarrow
In your model the energy of every photon is given by its frequency only, so it should be totally determined, but actually a single photon's energy is not well determined, and this is shown just from the fact that spectral lines have non-zero width.
I understand the argument. An analogy would be that I measure the diameter of a grain of sand on a beach with a very sensitive micrometer. I can know the size of the particular grain being measured, but I can only know the average size of grains of sand on the  beach after many measurements.

Then I could sift the grains through a screen with progressively larger openings and get a spectrum of sand sizes. But I can still suspect that the beach is made of a whole bunch of single grains of sand.

#### lightarrow

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##### can red light contain more energy than blue?
« Reply #17 on: 05/04/2009 17:06:58 »
Quote from: lightarrow
In your model the energy of every photon is given by its frequency only, so it should be totally determined, but actually a single photon's energy is not well determined, and this is shown just from the fact that spectral lines have non-zero width.
I understand the argument. An analogy would be that I measure the diameter of a grain of sand on a beach with a very sensitive micrometer. I can know the size of the particular grain being measured, but I can only know the average size of grains of sand on the  beach after many measurements.
But why for the sand's grains of one beach you get one value of the standard deviation and for the sand's grains of another beach you get another value? Why this fact is related with the time you need to measure a single grain?

#### Vern

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##### can red light contain more energy than blue?
« Reply #18 on: 05/04/2009 18:04:13 »
Well; we've beat upon this question of the number of wave cycles that comprise a photon for a little while; I don't know if we're closer to understanding it. When I search the web I get a reference to this thread I guess the question hasn't come up, or it isn't considered important in the physics community.

I guess it is only important when trying to visualize the dynamics of a gamma ray photon becoming a particle of matter. For piece of mind I need the process to be more than just poof, the photon becomes a particle.
« Last Edit: 05/04/2009 18:06:17 by Vern »

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##### can red light contain more energy than blue?
« Reply #18 on: 05/04/2009 18:04:13 »