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I Determination of electron energy in the 2 slit experiment

  1. Apr 20, 2016 #1

    drl

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    If w3e fire electrons thru the 2 slit we get an interference pattern showing the wave nature of the electron. Now if we cover one of the slits and fire electrons we get a bar like pattern on the screen. If we cover one slit, fire electrons and use a detector we would also get a bar like formation on the screen. Has any one checked to find if the kinetic energy of the electrons in the last 2 exps. were the same or of different values?Please avoid the use of difficult computations. I had enough trouble with long division.
     
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  3. Apr 20, 2016 #2

    Nugatory

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    Staff: Mentor

    The "bar-like pattern" is a diffraction pattern and it varies with the kinetic energy of the particle, so we get that energy measurement for free.
     
  4. Apr 20, 2016 #3

    drl

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    Many thanks .But is the electron hitting the screen when the detector is on have less energy than the electron hitting the screen when the detector is off. i.e. can the 2 slit quandary be explained as a difference of electron energies?
     
  5. Apr 20, 2016 #4

    Nugatory

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    What is this "quandary" that needs explaining? The point of the double-slit experiment is that the quantum mechanics correctly describes the way electrons interact with slits and classical mechanics does not. That's very surprising if you are assuming (as everyone did before QM was discovered) that electrons will behave like classical particles, but there's no quandary - QM works, classical mechanics doesn't.
     
  6. Apr 21, 2016 #5

    drl

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    Nugatort please. Does the electron hitting the screen when one slit is closed and the detector is turned on have the same amount of energy as the electron which hits the screen when one slit is closed and the detector is turned off?
     
  7. Apr 21, 2016 #6
    The detector turned on would normally (I think, necessarily) take away some energy in the process of detection. For instance a mirror would have to move a little. Since there's no quandary, it's impossible to say if this energy difference would explain it, if there were one.
     
  8. Apr 21, 2016 #7

    drl

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    Thank you thank you Didn't understand your reference to a mirror. Both you and Nugatory claim that there is no quandary in understanding the 2 slit exp. yet Dr.J. Al khalili claims that there is a Nobel prize awaiting the person who could explain it. The conciousness of the observer or 2 worlds explanation doesn't cut it for me, Too metaphysical Again, appreciate what you guys are doing for students of science.
     
  9. Apr 21, 2016 #8

    Nugatory

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    If I do the experiment over and over again, preparing the electron in exactly the same way every time, I will observe a range of electron energies at the screen. This will be true whether one slit is closed or not, whether a detector is present or not. Thus, there is no way of asking whether the electron energies are the same in the various cases - there's always a range of possible energies, and the ranges overlap.
     
  10. Apr 21, 2016 #9
    To detect a photon without absorbing it you can reflect it off a mirror. The mirror must move a little to signal the detection. Therefore it takes some energy from the photon. Imagine bouncing a ball off a wall that isn't very firm: the wall gives a bit, the ball bounces off a bit slower. As Nugatory says we're dealing with a range of energies so a detected photon isn't always less energetic than undetected; but I suppose on average that must be the case. If Nugatory says otherwise, believe him, not me.

    As for Dr. Al Khalili (whose knowledge I respect), it could be that our apparent difference amounts to nothing. If not - well, this is not a question about real physics, or math, it's just a matter of opinion. If he finds QM mysterious, I have no trouble accepting that it is mysterious - to him.
     
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