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  1. #1 photoelectric effect 
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    I want to ask you, do in the photoelectric effect, the electrons are opposing the electromagnetic field or they are excited from the energy?


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    photons above or equal to threshold frequency are absorbed by surface electrons. So yes they do excite them and with a 1:1 ratio so if they have enough energy they can escape the surface of the metal


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    Quote Originally Posted by Nevyn
    photons above or equal to threshold frequency are absorbed by surface electrons. So yes they do excite them and with a 1:1 ratio so if they have enough energy they can escape the surface of the metal
    Ok, and can you tell my why the cathode is put into glass balloon, when the glass absorbs ultraviolet radiation?
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    I think it is so a vacuum can be formed to stop impedement of the electron flow to the anode.
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    Glass balloon.....are you talking about some type of light bulb?

    Not only to do what he said, but also so that (if your talking about a light bulb) there isn't any air to be heated, and therefore melt itself.

    With the photoelectric effect- how do you determine the frequency of the light? Is frequency only an arbitrary way to describe the energy level?
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    Quote Originally Posted by Cold Fusion
    Glass balloon.....are you talking about some type of light bulb?

    Not only to do what he said, but also so that (if your talking about a light bulb) there isn't any air to be heated, and therefore melt itself.

    With the photoelectric effect- how do you determine the frequency of the light? Is frequency only an arbitrary way to describe the energy level?
    But I first look at the Heinrich Herz's experiment, which is electrifying of zinc bar of the top of the electroscope. First there is situated lamb which is emitting ultraviolet radiation and glass before it. When there is glass, the ultraviolet radiation can't pass through it, because it absorbs the ultraviolet radiation. Now why there is glass in form of light bulb? Do they also absorb visible light?
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    Quote Originally Posted by Cold Fusion
    Glass balloon.....are you talking about some type of light bulb?

    Not only to do what he said, but also so that (if your talking about a light bulb) there isn't any air to be heated, and therefore melt itself.

    With the photoelectric effect- how do you determine the frequency of the light? Is frequency only an arbitrary way to describe the energy level?
    no, he is talking about photocells or phototubes
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    What pass among the metal, ultraviolet radiation or visible light?
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    Quote Originally Posted by scientist91
    What pass among the metal, ultraviolet radiation or visible light?
    Probably just on the UV side.
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    Why the anode and cathode are put in vacuum photocell when the current flows from cathode to anode?
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    Quote Originally Posted by scientist91
    Why the anode and cathode are put in vacuum photocell when the current flows from cathode to anode?
    not entirely sure but photoelectrons flow from the cathode to the positively charged plate (anode). If there is air then this can stop/slow the flow and desrupt the current.
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    Exactly. Air does not conduct electricity, and therefore a vacume is needed. Think of a Jacob's Ladder. If you pull the two prongs to far apart, the electricity will not jump. In a vacume, there is less... Oh my gosh! I forgot the word again! I'm going brain dead!... less in the way ... crap! what was that word! I need some sleep.
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    Stuff?
    Of all the wonders in the universe, none is likely more fascinating and complicated than human nature.

    "Two things are infinite: the universe and human stupidity; and I'm not sure about the universe."

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    And why anode and cathode are put in vacuum instead of connecting them with wire? Is this picture correct?
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    Quote Originally Posted by scientist91
    And why anode and cathode are put in vacuum instead of connecting them with wire? Is this picture correct?
    The entire point of the experiment was to show that electrons would actually jump off the anode when hit by photons of sufficient energy. The whole thing of making a circuit by putting it under vacuum and adding a cathode was just the way they used to detect whether or not electrons were being knocked off the surface of the anode. If you see a current between the anode and the cathode, and if the anode and the cathode aren't physically connected, then the electrons must have been jumping off the anode.
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    And why in my text book says, that the kinetic energy of the electrons doesn't depends from the intensity of the radiation?
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    Quote Originally Posted by scientist91
    And why in my text book says, that the kinetic energy of the electrons doesn't depends from the intensity of the radiation?
    The kinetic energy of the electrons only depends on the energy of the photons (and the energy needed to knock the electron off the metal). The intensity of the light is the number of photons hitting the surface, not the energy of the photons. If you double the intensity of the light but leave the wavelength the same, you will knock twice as many electrons off - but all the electrons that leave the metal will still have the same kinetic energy. If reduce the wavelength of the photons hitting the surface (so the photons have more energy) but leave the intensity the same, you will knock off the same number of electrons - but all the electrons will now have more kinetic energy.
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    Quote Originally Posted by scientist91
    And why in my text book says, that the kinetic energy of the electrons doesn't depends from the intensity of the radiation?
    your text book is right if certain conditions are imposed.
    For Intensity to effect the kinetic energy of the electron, the photons have to be above threshold frequency. If they aren't then nothing happens no matter the intensity of the radiation.
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    Quote Originally Posted by Nevyn
    your text book is right if certain conditions are imposed.
    For Intensity to effect the kinetic energy of the electron, the photons have to be above threshold frequency. If they aren't then nothing happens no matter the intensity of the radiation.
    The intensity will never effect the kinetic energy of the electrons that are ejected - it will only change the number of electrons that are ejected. Only the wavelength of the photons will effect the kinetic energy.
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    Quote Originally Posted by Scifor Refugee
    Quote Originally Posted by Nevyn
    your text book is right if certain conditions are imposed.
    For Intensity to effect the kinetic energy of the electron, the photons have to be above threshold frequency. If they aren't then nothing happens no matter the intensity of the radiation.
    The intensity will never effect the kinetic energy of the electrons that are ejected - it will only change the number of electrons that are ejected. Only the wavelength of the photons will effect the kinetic energy.
    haha, oops, getting my intensity and frequency mixed up again, I hope I didn't do that in the exam :?
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    And what makes the current stronger? The more electrons ejected, or the speed of the electrons?
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    I want to know this: How do we know the wavelength of a photon, and what is it? I originally thought that it was the spacing between photons, but some people said that was wrong but didn't tell me what was right.
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    Quote Originally Posted by Cold Fusion
    I want to know this: How do we know the wavelength of a photon, and what is it? I originally thought that it was the spacing between photons, but some people said that was wrong but didn't tell me what was right.
    The wavelength of the photon is different with each part of the electromagnetic spectrum f = c/wavelength so wavelength = c/f

    I don't know what you are asking for with 'what is it?' please alliterate as to what
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    Quote Originally Posted by Cold Fusion
    I want to know this: How do we know the wavelength of a photon, and what is it? I originally thought that it was the spacing between photons, but some people said that was wrong but didn't tell me what was right.
    The wavelength of a photon seems self-contradictory but that is because of the wave-particle duality of light. It doesn't seem to make sense, but that's the way it is, It is the spacing between peaks of the electromagnetic field. The way you know the wavelength is by its color, by how it is refracted by a prism, by the diffraction pattern it makes from a diffraction grating, or things like that.
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    Quote Originally Posted by Cold Fusion
    I want to know this: How do we know the wavelength of a photon, and what is it? I originally thought that it was the spacing between photons, but some people said that was wrong but didn't tell me what was right.
    To add a little more to what some people have already said - all particles, including atom, a baseball, or the earth, have wavelengths. So photons, being particles, also have a wavelength.
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    I mean, did scientists randomly make a scale in order to compare different types/colors of EMR, or did they empiricaly find the wavelength through some method? And what method did they use? And what does the wavelength mean? The more I learn about this, the more confused I get...

    Yes, I do see allot of contradictions between wave/particle duality and the particle based methodology involved in this science.
    Of all the wonders in the universe, none is likely more fascinating and complicated than human nature.

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    Quote Originally Posted by Cold Fusion
    I mean, did scientists randomly make a scale in order to compare different types/colors of EMR, or did they empiricaly find the wavelength through some method?
    You can measure the wavelength with diffraction experiment.
    Yes, I do see allot of contradictions between wave/particle duality and the particle based methodology involved in this science.
    It can be very confusing. Just don't turn into one of those nuts who decide quantum physics is wrong and set out to make your own "improved" theory without any formal training.
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    But do they know what the nm spacing means? Spacing between what? I just need to visualize this a little better.

    Don't worry...I believe in those PHd's who work their asses off 24/7 for the sake of science.
    Of all the wonders in the universe, none is likely more fascinating and complicated than human nature.

    "Two things are infinite: the universe and human stupidity; and I'm not sure about the universe."

    "Great spirits have always found violent opposition from mediocrities. The latter cannot understand it when a man does not thoughtlessly submit to hereditary prejudices but honestly and courageously uses his intelligence"

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    Quote Originally Posted by Cold Fusion
    But do they know what the nm spacing means? Spacing between what? I just need to visualize this a little better.

    Don't worry...I believe in those PHd's who work their asses off 24/7 for the sake of science.
    spacing between the atoms themselves, otherwise you wouldn't have a gap small enough for the electrons to defract through. They use thin sheets of nickle. The spacing between the atoms is 1/10 of a nanometer I think whish is an Ankstrom or something like that
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    Atoms or photons? Do you mean the atoms that emit the photons?
    Which would mean that the spacing determines the color...why is that?

    And; what colors you see are determined by what colors are absorbed by the material, right? When you say colors absorbed, that would imply that there are types of photons that are emitted from the original source-how is that possible? Aren't all original photons created equally? How can there be a RGB photon type?
    Of all the wonders in the universe, none is likely more fascinating and complicated than human nature.

    "Two things are infinite: the universe and human stupidity; and I'm not sure about the universe."

    "Great spirits have always found violent opposition from mediocrities. The latter cannot understand it when a man does not thoughtlessly submit to hereditary prejudices but honestly and courageously uses his intelligence"

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  32. #31  
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    Quote Originally Posted by Cold Fusion
    Atoms or photons? Do you mean the atoms that emit the photons?
    Which would mean that the spacing determines the color...why is that?

    And; what colors you see are determined by what colors are absorbed by the material, right? When you say colors absorbed, that would imply that there are types of photons that are emitted from the original source-how is that possible? Aren't all original photons created equally? How can there be a RGB photon type?
    sorry, I thought we had moved onto youngs slits experiment (not sure spelling is right).

    Young fired a laser at an obstacle with 2 slits in it. this meant that as light passed through the slits it interferred with itself and caused a concentric ring interferance pattern, which is a phenomenon of waves.
    To prove that electrons can behave as waves in accordance to wave-particle duality electrons were fired from an electron gun at a nickle plate (spacing between atoms had to be used because diffraction only occurs between distances = to or less than the wavelength).
    Because the deBroglie wavelength = h/mv, the faster the electrons go, the longer the wavelength and the smaller the difference between concentric rings.

    'colour' is not absorbed by the surface, it's just lights frequency changes as it reflects of a surface as energy is absorbed. So colour is dependant on frequency
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    Quote Originally Posted by Cold Fusion
    I mean, did scientists randomly make a scale in order to compare different types/colors of EMR, or did they empiricaly find the wavelength through some method? And what method did they use? And what does the wavelength mean? The more I learn about this, the more confused I get...

    Yes, I do see allot of contradictions between wave/particle duality and the particle based methodology involved in this science.
    Take a look at the wikipedia article.
    http://en.wikipedia.org/wiki/Light
    About 2/3 of the way down the page is a sketch showing the electric and magnetic fields and the wavelength. This should give you a better idea of what is meant.

    Historically, Newton believed light consisted of "corpuscles" and this was the accepted view up until Young's double slit experiment, so I suppose the double slit was the first method of measuring wavelength. The wavelenght can be calculated by measuring the distance between diffraction fringes in the double slit experiment.
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    Quote Originally Posted by Nevyn
    Young fired a laser at an obstacle with 2 slits in it.
    No, they didn't have lasers in 1800. He used a beam of sunlight.
    Because the deBroglie wavelength = h/mv, the faster the electrons go, the longer the wavelength and the smaller the difference between concentric rings.
    I think you have that backwards. Faster electrons have more energy, greater frequency, and shorter wavelengths.
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    Then what about the idea that certain colors are absorbed due to their frequency, or was it energy level? I'm lost.....
    Of all the wonders in the universe, none is likely more fascinating and complicated than human nature.

    "Two things are infinite: the universe and human stupidity; and I'm not sure about the universe."

    "Great spirits have always found violent opposition from mediocrities. The latter cannot understand it when a man does not thoughtlessly submit to hereditary prejudices but honestly and courageously uses his intelligence"

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    I want to ask you what happens with bar code readers, when the light is touching the bar code (but the white parts of the bar code), do they reflect in the photodiode of the bar code reader?
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    btw- Can you recognize this? Do you know what happens, when the light will touch the white parts? Will be sound produced?
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    None, knows? It is Motion picture sound
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