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Thread: The Photoelectric effect, determining the electron

  1. #1 The Photoelectric effect, determining the electron 
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    It is said that you can not determine the exact location of an electron because you determine things with photons and the photon knocks the electron from its current location so the reading would be wrong.

    Say the photon hits it the electron off cource with one newton of force(way over actual) but then it was countered with another photon on the oppisite side of the electron. Now if the electron is say hit by two photons with one newton of force from oppisite directions the net force would be 0 and neither the electrons speed nor direction would be changed but the photon(s) would reflect back and show the exact location of the electron.


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    Forum Radioactive Isotope MagiMaster's Avatar
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    Yeah, but since you don't know where the electron is in the first place, how do you know where to put the second photon?


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  4. #3  
    Moderator Moderator Janus's Avatar
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    Quote Originally Posted by MagiMaster
    Yeah, but since you don't know where the electron is in the first place, how do you know where to put the second photon?
    Exactly, said method would require that you already know the exact position and momentum of the electron.
    "Men are apt to mistake the strength of their feelings for the strength of their argument.
    The heated mind resents the chill touch & relentless scrutiny of logic"-W.E. Gladstone


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  5. #4 Re: The Photoelectric effect, determining the electron 
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    Quote Originally Posted by Raymond K
    It is said that you can not determine the exact location of an electron because you determine things with photons and the photon knocks the electron from its current location so the reading would be wrong.

    Say the photon hits it the electron off cource with one newton of force(way over actual) but then it was countered with another photon on the oppisite side of the electron. Now if the electron is say hit by two photons with one newton of force from oppisite directions the net force would be 0 and neither the electrons speed nor direction would be changed but the photon(s) would reflect back and show the exact location of the electron.
    The uncertaintly principle is more fundamental than that and cannot be overcome by refining experimental technique.

    At the fundamental theoretical level when one makes an mesurement to determine an observable what one does is apply a Hermitian operator to the wave function of the particle. That operator actually changes the wave function so that to make a subsequent measurement you apply another operator to the wave function that has been changed by the first one. Those operators do not commute, so that if you apply operator A and then operator B you get a different answer than if you apply operator B and then operator A.

    This is most easily illustrated by the position and momentum operators. One is multiplication by "x" and the other is differentiation with respect to x. So if you have a wave function you can see what happens if you find position and them momentum versus momentum and then position. It goes like this
    but and those expressions are not in general equal.
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  6. #5  
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    Quote Originally Posted by MagiMaster
    Yeah, but since you don't know where the electron is in the first place, how do you know where to put the second photon?

    You have a constant flow of photons.
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    Forum Masters Degree Numsgil's Avatar
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    As DrRocket says, it's not just that the photon changes the course of the electron. Any observation whatsoever, by it's very nature, will cause the wave function to "collapse" in one direction and "expand" in the other. Like knowing position causes fuzzier momentum. It's not something you can get around, it's as real and rooted in the way things work as electromagnetism or gravity.
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    Quote Originally Posted by Numsgil
    As DrRocket says, it's not just that the photon changes the course of the electron. Any observation whatsoever, by it's very nature, will cause the wave function to "collapse" in one direction and "expand" in the other. Like knowing position causes fuzzier momentum. It's not something you can get around, it's as real and rooted in the way things work as electromagnetism or gravity.

    Now how does that all work, magic?
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    Quote Originally Posted by Raymond K
    Now how does that all work, magic?
    I does sound like magic but remember we build our intuition on how the world works at very slow speeds and on a large length scale . When we start to investigate the world of QM's things just behave differentially. The weirdness of QM was hard to except by many scientists in the early 1900's.

    You can argue with the experimentalist but you can't argue with nature.

    If you really what to appreciate QM you must learn the math. (The same is true for relativity.)
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  10. #9  
    Forum Masters Degree Numsgil's Avatar
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    Quote Originally Posted by Raymond K
    Quote Originally Posted by Numsgil
    As DrRocket says, it's not just that the photon changes the course of the electron. Any observation whatsoever, by it's very nature, will cause the wave function to "collapse" in one direction and "expand" in the other. Like knowing position causes fuzzier momentum. It's not something you can get around, it's as real and rooted in the way things work as electromagnetism or gravity.

    Now how does that all work, magic?
    Yes.

    Well, how does gravity work? We can talk about bent space time, but there's always a deeper level of how and why. So yes, magic.
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  11. #10  
    Forum Radioactive Isotope MagiMaster's Avatar
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    Well, as Arthur C. Clarke said, "any sufficiently advanced technology is indistinguishable from magic." Another way to say that is anything we don't understand well enough will look like magic.
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  12. #11  
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    Quote Originally Posted by Numsgil
    Quote Originally Posted by Raymond K
    Quote Originally Posted by Numsgil
    As DrRocket says, it's not just that the photon changes the course of the electron. Any observation whatsoever, by it's very nature, will cause the wave function to "collapse" in one direction and "expand" in the other. Like knowing position causes fuzzier momentum. It's not something you can get around, it's as real and rooted in the way things work as electromagnetism or gravity.

    Now how does that all work, magic?
    Yes.

    Well, how does gravity work? We can talk about bent space time, but there's always a deeper level of how and why. So yes, magic.

    My point exactly, where does it all stop? See thats where i think i greater power comes in and logic and mathmatics goes out. But as i remember einstein was finding a theory for "everything" that could also be the answer there is one component of everything and it combines to form the difference between light and a chair.
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