ATAR Notes: Forum
VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Physics => Topic started by: NE2000 on November 01, 2009, 12:11:31 pm
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Ok I've got a question about this. Taylor's experiment essentially sent one photon at a time and observed diffraction and what appeared to be an interference pattern over the course of three months. But my question is: is this really interference? Because all the concepts of interference, of in phase and out of phase waves, don't appear on first glance to hold. The same question arises for similar patterns produced when single electrons are sent to be diffracted on some sort of screen. I read that it shows the distribution of electrons along a pdf, which shows wave-like properties as it's not a shadow. But why are there areas that are 'dense' with electrons and areas that are not so dense.
However, when you shine a beam of electrons through a crystal diffraction grating, then the X-ray like diffraction pattern you get is due to interference between waves right, like we have in light? Or is this more to do with the VCE mystery of single-slit diffraction?
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It's not interference per se, but as you said, a probability distribution. As far as I'm aware, physicists aren't sure exactly why such a distribution occurs, but it imitates what we'd expect form an interference pattern. It just supports the notion that light isn't really a particle, nor a wave - it's more of an entity that we can't liken to anything else.
Single slit diffraction essetially demonstrates interference as well: there's a path difference between light exiting different parts of the slit, and hence interference (or a probability distribution imitating interference) occurs. The same sort of thing happens with electrons being passed though crystal structures. As the electrons have a wavelength, they're going to display properties of diffraction and intererence. There's also a path difference, which depends on the spacing between the layers of the crystal, which hence influences the spacing between the rings on the pattern.
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As appianway said the location of the electron is given by a probability distribution (schrodinger wave equation). Until the electron is observed, it exists in a superposition of these different possible states. This means the electron can interfere with itself. When the electron is detected, the wavefunction collapses and the electron occupies one of these states. This is why each electron still only leaves a dot on the screen.