Light's Reach: How Far Does 1 Candela's Luminosity Go?

[Drakkith]

Well I would just say the waves have to be the right frequency, that seems a bit more logical than saying the particles have the right frequency, because the idea of particles having a frequency is a bit 'odd', we normally speak of the frequency of waves not particles. (well I do).

I mean there are two ways of looking at it for the energy from light, you can say the wave has a bigger amplitude, or that more waves of a smaller amplitude are emitted per second.

Turning it around somewhat you could say when you turn up a light it emits bigger particles of light, or maybe that's not a good analogy?

So to me the photo-electric experiment is not very helpful either way.

The right frequency? No, they have to be above a certain frequency. ANY frequency above that can eject an electron from the surface of a materiel. NO frequency under that will eject one however.

Amplitude has NO meaning with light. It is a proven fact, like the photoelectric effect shows, that only a change in frequency can raise or lower the energy of a photon.

 

[AtomicJoe]

If light were really purely a wave, it would be possible to cut down the intensity by any amount, including an amount where it wouldn't be enough to cut loose an electron. .

Well by your definition of a wave yes, but I using a different idea of a wave, a wave pulse if you like.

Well, one exists, one doesn't: there is no such thing as a "quantized wave". .

I don't really have a problem with the concept.
A tsunami could be considered a quantised wave for example.
Albeit a large one.

Except that you're now saying that there is a minimum amplitude to a wave. That doesn't jive with how waves work.

Well yes from a particular source there could be. Like dropping pebbles all the same size into a pond.

Moreover, this contradicts what you said earlier about waves being continuous and omni directional - while they may not need to be omni directional, neither are they completely discrete. Ie, with the double-slit experiment, there is no way for a wave-based light to create a single dot on a detector.

I don't think I said they were continuous as such, omni directional yes.

Creating a single dot is, I admit, somewhat more problematic, on the same scale as you getting your particle through two slits at the same time.

I have never seen the experiment done myself, it takes some believing!

 

[AtomicJoe]

The right frequency? No, they have to be above a certain frequency. ANY frequency above that can eject an electron from the surface of a materiel. NO frequency under that will eject one however.

Amplitude has NO meaning with light. It is a proven fact, like the photoelectric effect shows, that only a change in frequency can raise or lower the energy of a photon.

So what happens when you increase the frequency?

Is the electron released with more energy?
Or is there some 'spare light' left over?

Also if it has no amplitude, how can it have a frequency?

 

[russ_watters]

Well by your definition of a wave yes, but I using a different idea of a wave, a wave pulse if you like.

Well, you're starting to make up a definition that sounds more and more like how light really works and less and less like the actual definition of wave. While that's an improvement, it would be better if you'd just acknowledge that you're no longer describing the (not my) definition of a wave. Words have specific meanings and you're really not entitled to make them up as you go along.

I don't really have a problem with the concept.
A tsunami could be considered a quantised wave for example.
Albeit a large one.

That's not what the word "quantized" means.

Well yes from a particular source there could be. Like dropping pebbles all the same size into a pond.

That's just not how it works.

I don't think I said they were continuous as such, omni directional yes.

Waves are continuous, which is why they cause interference patterns.

 

[Drakkith]

So what happens when you increase the frequency?

Is the electron released with more energy?
Or is there some 'spare light' left over?

Also if it has no amplitude, how can it have a frequency?

As you increase the frequency, the electrons are ejected with more and more energy. There is not spare light left over.

Don't know about the amplitude thing though. I just know I've never heard of amplitude of a single EM wave mattering for anything.

 

[sophiecentaur]

Like Russ said, that is incorrect. There is overwhelming evidence that light has properties of BOTH waves and particles. Look up the photoelectric effect.

The photoelectric effect does not indicate particulate nature. It tells us that the energy is quantised. These two are entirely distinct properties.
The word 'particle' is used by people because it is less intellectually demanding.

 

[AtomicJoe]

Well, you're starting to make up a definition that sounds more and more like how light really works and less and less like the actual definition of wave. While that's an improvement, it would be better if you'd just acknowledge that you're no longer describing the (not my) definition of a wave. Words have specific meanings and you're really not entitled to make them up as you go along.
That's not what the word "quantized" means. That's just not how it works. Waves are continuous, which is why they cause interference patterns.

There are different types of waves, for example a shock wave, which is more like a quantised pulse. I am sure you can have a un-continuous wave for example I am sure the photoelectric will work in reverse?
I mean surely the process which releases the single photo for the double slit experiment is the effect in reverse. A single particle detected through the slit would not be enough to be called a pattern.

 

[sophiecentaur]

A shockwave is not "quantised". What energy is associated with the energy of the individual molecules or the modes of bulk movement? Do you know what is meant by a quantum?

 

[zeromodz]

The further away you go the less photons per unit of time will hit the detector..

So if you were to take the limit as r goes to infinity, the light will contain zero photons? What happens to the photons as they travel. Why do you get less photons per unit of time if all photons travel at the same speed?

 

[AtomicJoe]

A shockwave is not "quantised". What energy is associated with the energy of the individual molecules or the modes of bulk movement? Do you know what is meant by a quantum?

It mean amount, if is the same root as quantity.

 

[Drakkith]

So if you were to take the limit as r goes to infinity, the light will contain zero photons? What happens to the photons as they travel. Why do you get less photons per unit of time if all photons travel at the same speed?

No. Individual photons are emitted in random directions. Because of this, the further away you are, you less photons you will detect per second for example. They spread out if you will. If you had a perfect detector and no interference and nothing to block the light, AND you had an infinite time to wait, you could go ANY distance from an object and eventually detect a photon from it.

 

[Drakkith]

It mean amount, if is the same root as quantity.

From wikipedia on Quantum:


In physics, a quantum (plural: quanta) is the minimum amount of any physical entity involved in an interaction. Behind this, one finds the fundamental notion that a physical property may be "quantized," referred to as "the hypothesis of quantization".[1] This means that the magnitude can take on only certain discrete values. There is a related term of quantum number. An example of an entity that is quantized is the energy transfer of elementary particles of matter (called fermions) and of photons and other bosons

A shock wave is NOT quantized. An example of quantization is the energy levels of electrons in atoms. They can ONLY have certain values, integers of N. It CANNOT have 1/2 N for example.

For light this means that the entire photon is "One entity". It can only be absorbed or emitted as a whole unit. You cannot split it in half.

A classic wave, like in a shock wave, can be split, absorbed, and will transfer any amount of the energy behind it to something else. This is NOT the case for light.

 

[sophiecentaur]

It mean amount, if is the same root as quantity.

The word has a much more specific meaning in QM. A quantum is a tiny amount of energy- the minimum energy that takes part in the interaction between an EM wave and an atom, molecule or arrangement of molecules. Some people refer to it as a particle by I like just to stick to the energy definition.