Amplitude question

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Amplitude question

#1  Postby LjSpike » Apr 12, 2017 12:01 pm

Transverse waves have amplitude. In mechanical transverse waves (e.g. a wave on the open ocean) amplitude is twice the height of the wave, it's a physical dimension of the wave. You could then say amplitude of wave is proportional to height of wave.

Does this hold true for a light wave? Does a single light wave, literally have a height as a result of it having amplitude?
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Re: Amplitude question

#2  Postby Cito di Pense » Apr 12, 2017 12:42 pm

LjSpike wrote:Transverse waves have amplitude. In mechanical transverse waves (e.g. a wave on the open ocean) amplitude is twice the height of the wave, it's a physical dimension of the wave. You could then say amplitude of wave is proportional to height of wave.

Does this hold true for a light wave? Does a single light wave, literally have a height as a result of it having amplitude?


The oscillations of a field have an amplitude, else they couldn't be amplified. Pressure waves have amplitude as well, expressed as oscillations in the local density of the medium through which the wave is transmitted, relative to the ambient density. That's why, when you dial your amp to '11', your eardrums feel it.
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Re: Amplitude question

#3  Postby newolder » Apr 12, 2017 2:48 pm

In electromagnetism, amplitude is defined as the difference between maximum and minimum values of the component electric and magnetic waves.
Given Maxwell's four equations (which are based on observation) we have shown that electromagnetic waves must exist as a consequence. They can have any amplitude E0 (with B0 depending on E0 as will be shown later), any wavelength λ, and be retarded or advanced by any phase φ, but they can only travel through empty space at one wave speed c.

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Re: Amplitude question

#4  Postby crank » Apr 12, 2017 2:55 pm

There isn't anything in light that could be considered a literal 'height'. It works with fluid waves because the energy in such waves is in the height, or you could say the waves are a positional thing, so the height is the amplitude. How is 'amplitude' twice the height? Isn't that the difference between peak-to-peak vs 0-to-peak? Wave heights are usually considered to be from sea level, so 8 ft waves should have 8 ft troughs also. I think that's correct??
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Re: Amplitude question

#5  Postby twistor59 » Apr 12, 2017 6:00 pm

crank wrote:There isn't anything in light that could be considered a literal 'height'. It works with fluid waves because the energy in such waves is in the height, or you could say the waves are a positional thing, so the height is the amplitude. How is 'amplitude' twice the height? Isn't that the difference between peak-to-peak vs 0-to-peak? Wave heights are usually considered to be from sea level, so 8 ft waves should have 8 ft troughs also. I think that's correct??


No there isn't a physical distance associated with the amplitude value. As others have said, you can apply the term "amplitude" to the max instantaneous electric (or magnetic) field component, but this is not measured in meters.
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Re: Amplitude question

#6  Postby LjSpike » Apr 15, 2017 12:06 pm

crank wrote:There isn't anything in light that could be considered a literal 'height'. It works with fluid waves because the energy in such waves is in the height, or you could say the waves are a positional thing, so the height is the amplitude. How is 'amplitude' twice the height? Isn't that the difference between peak-to-peak vs 0-to-peak? Wave heights are usually considered to be from sea level, so 8 ft waves should have 8 ft troughs also. I think that's correct??


Height in waves as a physical descriptor seems to sometimes work from trough-to-peak and sometimes 0-to-peak. The latter seems to occur less often, although I do agree makes more sense.

Thats interesting to know then, that amplitude in electromagnetic waves isn't a literal height.
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Re: Amplitude question

#7  Postby Cito di Pense » Apr 19, 2017 2:39 pm

LjSpike wrote:
Thats interesting to know then, that amplitude in electromagnetic waves isn't a literal height.


There's no material medium that is being displaced. That's why the 'luminiferous ether' view of electromagnetic wave transmission went away.
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Re: Amplitude question

#8  Postby LjSpike » Apr 19, 2017 9:44 pm

Cito di Pense wrote:
LjSpike wrote:
Thats interesting to know then, that amplitude in electromagnetic waves isn't a literal height.


There's no material medium that is being displaced. That's why the 'luminiferous ether' view of electromagnetic wave transmission went away.


Mhm. I simply was inquiring as to if it was a physical dimension amplitude as I'm just naively constructed an undoubtedly heavily flawed explanation of the photoelectric effect using wave theory. The only point I'm truly fully stuck on is amplitude effecting electrons emitted per second, which in and of itself seems to go against the fact that photoelectrons are emitted with no delay...
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Re: Amplitude question

#9  Postby Cito di Pense » Apr 21, 2017 1:43 pm

LjSpike wrote:
Cito di Pense wrote:
LjSpike wrote:
Thats interesting to know then, that amplitude in electromagnetic waves isn't a literal height.


There's no material medium that is being displaced. That's why the 'luminiferous ether' view of electromagnetic wave transmission went away.


Mhm. I simply was inquiring as to if it was a physical dimension amplitude as I'm just naively constructed an undoubtedly heavily flawed explanation of the photoelectric effect using wave theory. The only point I'm truly fully stuck on is amplitude effecting electrons emitted per second, which in and of itself seems to go against the fact that photoelectrons are emitted with no delay...


What's the intensity of the radiation? Some measure of the flux of energy normalized on a unit area. More photons per second per unit area, more photoelectrons. If something is varying in time or space (like your photoelectric example -- something resulting in more -- or fewer -- electrons emitted per second) then you can refer to the amplitude of the variation, and refer it to some base. Measurement units like MKS or CGS can be referred to as 'dimensions' of a problem, but only the distance units (meters or centimeters) reference an explicitly 'spatial' dimension.

You could vary the 'amplitude' of the incoming radiation by orienting the incoming beam obliquely. This affects the flux, too.
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Re: Amplitude question

#10  Postby LjSpike » Apr 26, 2017 3:19 pm

Cito di Pense wrote:

What's the intensity of the radiation? Some measure of the flux of energy normalized on a unit area. More photons per second per unit area, more photoelectrons. If something is varying in time or space (like your photoelectric example -- something resulting in more -- or fewer -- electrons emitted per second) then you can refer to the amplitude of the variation, and refer it to some base. Measurement units like MKS or CGS can be referred to as 'dimensions' of a problem, but only the distance units (meters or centimeters) reference an explicitly 'spatial' dimension.

You could vary the 'amplitude' of the incoming radiation by orienting the incoming beam obliquely. This affects the flux, too.


That was a rather jargon filled comment. Perhaps try simplifying it a tad?
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Re: Amplitude question

#11  Postby Cito di Pense » Apr 26, 2017 4:37 pm

LjSpike wrote:
Cito di Pense wrote:

What's the intensity of the radiation? Some measure of the flux of energy normalized on a unit area. More photons per second per unit area, more photoelectrons. If something is varying in time or space (like your photoelectric example -- something resulting in more -- or fewer -- electrons emitted per second) then you can refer to the amplitude of the variation, and refer it to some base. Measurement units like MKS or CGS can be referred to as 'dimensions' of a problem, but only the distance units (meters or centimeters) reference an explicitly 'spatial' dimension.

You could vary the 'amplitude' of the incoming radiation by orienting the incoming beam obliquely. This affects the flux, too.


That was a rather jargon filled comment. Perhaps try simplifying it a tad?


It would be better if you would restate your first remaining question. Do some more reading on the photoelectric effect and see if you can focus your question a little more. Don't try to address the photoelectric effect with wave theory. It's a photonic phenomenon, and one of the early results that finally led to a formal quantum theory of light and matter.
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Re: Amplitude question

#12  Postby LjSpike » Apr 29, 2017 9:58 am

Cito di Pense wrote:
LjSpike wrote:
Cito di Pense wrote:

What's the intensity of the radiation? Some measure of the flux of energy normalized on a unit area. More photons per second per unit area, more photoelectrons. If something is varying in time or space (like your photoelectric example -- something resulting in more -- or fewer -- electrons emitted per second) then you can refer to the amplitude of the variation, and refer it to some base. Measurement units like MKS or CGS can be referred to as 'dimensions' of a problem, but only the distance units (meters or centimeters) reference an explicitly 'spatial' dimension.

You could vary the 'amplitude' of the incoming radiation by orienting the incoming beam obliquely. This affects the flux, too.


That was a rather jargon filled comment. Perhaps try simplifying it a tad?


It would be better if you would restate your first remaining question. Do some more reading on the photoelectric effect and see if you can focus your question a little more. Don't try to address the photoelectric effect with wave theory. It's a photonic phenomenon, and one of the early results that finally led to a formal quantum theory of light and matter.


It's not a photonic phenomenon nor is it a wave phenomenon, it's simply that we try to address it as one or the other as we can't get our heads around it being both. There is no reason to not attempt to explain it as a wave phenomenon, if one can achieve such an explanation. After all, light has switched back and forth between being explained as photons and waves in the past, first with Newton I believe, stating it as particles, then to waves, then back to photons.

I also believe It's also been determined that huge amplitudes can cause emission below the threshold frequency, which wouldn't settle down too nicely with the current explanation of how it works with photons as in that case the frequency should be the determinant factor in energy passed on (and therefore emission).

Simply put though, the point which I can't get to properly explaining is why an increase in amplitude increases photoelectrons emitted per second. I presume in a photonic interpretation one would state amplitude increases causes more photons to hit the surface per second, however with wave theory I can't quite work out an even tangible explanation. On the other hand, I can at least begin to explain why huge amplitudes would cause emission at lower frequencies...

Now I could read through tonnes of scientific papers to try and work out what was meant in that previous comment, however I'd have to go through tonnes before I found some that were less heavy on jargon, and I can't ask them to rephrase it, unlike here, I can ask for some rephrasing and/or analogies to help me understand the points presented.
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Re: Amplitude question

#13  Postby Cito di Pense » Apr 29, 2017 10:22 am

LjSpike wrote:
Cito di Pense wrote:
LjSpike wrote:
Cito di Pense wrote:

What's the intensity of the radiation? Some measure of the flux of energy normalized on a unit area. More photons per second per unit area, more photoelectrons. If something is varying in time or space (like your photoelectric example -- something resulting in more -- or fewer -- electrons emitted per second) then you can refer to the amplitude of the variation, and refer it to some base. Measurement units like MKS or CGS can be referred to as 'dimensions' of a problem, but only the distance units (meters or centimeters) reference an explicitly 'spatial' dimension.

You could vary the 'amplitude' of the incoming radiation by orienting the incoming beam obliquely. This affects the flux, too.


That was a rather jargon filled comment. Perhaps try simplifying it a tad?


It would be better if you would restate your first remaining question. Do some more reading on the photoelectric effect and see if you can focus your question a little more. Don't try to address the photoelectric effect with wave theory. It's a photonic phenomenon, and one of the early results that finally led to a formal quantum theory of light and matter.


It's not a photonic phenomenon nor is it a wave phenomenon, it's simply that we try to address it as one or the other as we can't get our heads around it being both. There is no reason to not attempt to explain it as a wave phenomenon, if one can achieve such an explanation. After all, light has switched back and forth between being explained as photons and waves in the past, first with Newton I believe, stating it as particles, then to waves, then back to photons.

I also believe It's also been determined that huge amplitudes can cause emission below the threshold frequency, which wouldn't settle down too nicely with the current explanation of how it works with photons as in that case the frequency should be the determinant factor in energy passed on (and therefore emission).

Simply put though, the point which I can't get to properly explaining is why an increase in amplitude increases photoelectrons emitted per second. I presume in a photonic interpretation one would state amplitude increases causes more photons to hit the surface per second, however with wave theory I can't quite work out an even tangible explanation. On the other hand, I can at least begin to explain why huge amplitudes would cause emission at lower frequencies...

Now I could read through tonnes of scientific papers to try and work out what was meant in that previous comment, however I'd have to go through tonnes before I found some that were less heavy on jargon, and I can't ask them to rephrase it, unlike here, I can ask for some rephrasing and/or analogies to help me understand the points presented.


You're right, Spike. Greater numbers of incident photons above the threshold frequency will increase emission of photoelectrons.

What will you have when you finally understand, Spike? What will you have when you can make up answers for your own 'why' questions, such as why huge amplitudes would cause emission at lower frequencies (based on sources you have yet to cite)? Will you ever be able to just shut up and calculate? Read a fricking textbook on quantum mechanics, but learn about vectors and matrices first.

I tried to get you to think about it in terms of magnitude or intensity (of a radiation field) instead of amplitude (which you may be confusing with probability amplitude, but I have no way of knowing, the way you're thrashing around, here as you continue to try to apply wave phenomena to the photoelectric effect because you read somewhere (and haven't cited it) that "it's been determined that huge amplitudes (sic) can cause emission below the threshold frequency". Yes, Spike, photons have frequencies, and photonic processes have statistics. When you're ready to learn something, begin at the beginning.

You could start with the wikipedia article on the photoelectric effect. I quote:

Below that threshold, no electrons are emitted from the metal regardless of the light intensity or the length of time of exposure to the light (rarely, an electron will escape by absorbing two or more quanta.
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Re: Amplitude question

#14  Postby LjSpike » May 01, 2017 3:18 pm

Cito di Pense wrote:
What will you have when you finally understand, Spike? What will you have when you can make up answers for your own 'why' questions

Because, that is science. Questioning why something occurs.

Cito di Pense wrote:
Read a fricking textbook on quantum mechanics, but learn about vectors and matrices first.

Perhaps I will eventually, it'll certainly have less animosity and hostility even if it won't be able to tailor its responses to clarify any misunderstood points.

Cito di Pense wrote:
(based on sources you have yet to cite)? Will you ever be able to just shut up and calculate?


I tried to do a quick look for the source, I can't remember where I saw it, I'll try a bit more later on to see if I can find the source I read it from for you. Calculation is only part of physics though, thinking and discussing is a large part too. You have to know what you want to calculate and how to go about calculating it, before you actually begin calculations.


Cito di Pense wrote:
but learn about vectors and matrices first.

Vectors I've learnt about but I'll make sure to read up on matrices. Perhaps the only actual useful and/or productive information in your comment.
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Re: Amplitude question

#15  Postby Cito di Pense » May 01, 2017 4:27 pm

LjSpike wrote:it won't be able to tailor its responses to clarify any misunderstood points.


That's what you pay your tutors for, LJSpike. It's one way you can motivate yourself to respect the expertise of those who have more expertise than you do, instead of flailing around in an anonymous internet forum where the people who have the expertise really to help you don't have the time to waste on your brand of protest. You've had several lovely chances (from several different posters) to absorb the answer to what was, after all, a rather simple question on 'amplitude' in analysing radiation. To get beyond the simple analysis, you're going to have to hold yourself responsible for proving that you understand something, and that very much is going to be by doing calculations in the early going, instead of wrangling with wave-particle duality like some blithering philosopher.

LjSpike wrote:Questioning why something occurs.


Like some philosopher, Spike? No, for starters you should think about showing you understand how some physics is modeled. It works best if you begin at the beginning.

LjSpike wrote:I tried to do a quick look for the source, I can't remember where I saw it


Then it's not something you 'know', and you can't communicate coherently with anyone else about it, because you don't have access to anyone else's critique of it. It's a shabby way of conducting a conversation about physics.
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Re: Amplitude question

#16  Postby LjSpike » May 06, 2017 6:48 pm

Cito di Pense wrote:
LjSpike wrote:it won't be able to tailor its responses to clarify any misunderstood points.


That's what you pay your tutors for, LJSpike. It's one way you can motivate yourself to respect the expertise of those who have more expertise than you do, instead of flailing around in an anonymous internet forum where the people who have the expertise really to help you don't have the time to waste on your brand of protest. You've had several lovely chances (from several different posters) to absorb the answer to what was, after all, a rather simple question on 'amplitude' in analysing radiation. To get beyond the simple analysis, you're going to have to hold yourself responsible for proving that you understand something, and that very much is going to be by doing calculations in the early going, instead of wrangling with wave-particle duality like some blithering philosopher.

LjSpike wrote:Questioning why something occurs.


Like some philosopher, Spike? No, for starters you should think about showing you understand how some physics is modeled. It works best if you begin at the beginning.

LjSpike wrote:I tried to do a quick look for the source, I can't remember where I saw it


Then it's not something you 'know', and you can't communicate coherently with anyone else about it, because you don't have access to anyone else's critique of it. It's a shabby way of conducting a conversation about physics.


1) I am not protesting, I came to query a point on amplitude in electromagnetic waves, that is all.
2) Why pay a tutor? This magical thing called the internet has millions of people on it, from all around the world, many specialists in every imaginable field (and some I couldn't begin to imagine) exist in here. Scholarly articles from universities and research labs everywhere are catalogued in this great library and school of thought.
3) It's my choice to wrangle with particle-wave duality. Don't insult philosophers, while Newtons Flaming Laser Sword and Occam's Razor are both awesomely named principles, and have their applications at points, to treat them as a law is to deny any progress to be conducted. Before you begin a venture, you have no way of knowing its ending.
4) I accepted the simple answer, your the one who then stumbled along, threw jargon at me, and then threw a temper tantrum when you were asked to simplify it down.


To summarise, chill out, and just don't throw a hissy fit over my spontaneous endeavours. I know that it is almost certain that nothing will come from my little endeavour, but that is not a reason to not try. I'm sure if we all followed your philosophy of just "don't try push the boundaries or do anything new" many of the inventions that bless our little blue marble would not have come to be. We would not have stepped out into space, nor touched the deepest depths of the ocean. I likewise doubt we'd have the internet, and as a result, this little forum for us to discuss and debate on, if we followed your philosophy. While your free to follow that train of thought of not enduring through some of the most random of tasks, or wondering things which have no answers yet, please don't force it on to me.

Edit: One Irony I do find, you insult being a philosopher with the description of "blithering" yet the chunk of the forum you are most active on is the Philosophy section. Either you have a lot of time to enforce your views onto others, or you enjoy contradiction?
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