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Gaussian wave packets

  1. Oct 18, 2008 #1
    If you imagine a string, the first part of the string (that the gaussian looking wave peak is moving along) has thicker mass density than the latter part of the string. (so it's essentially a thick bit of string going on to a thinner bit).
    What would happen when the wavepacket reaches the latter section? I think you will get an upright reflected wavepacket and also an upright transmitted wavepacket, is this correct?
    (the reason I think this is because I'm thinking it's like the wavefunction of a free particle, colliding with a stationary particle of lower mass, so it's analogous to an elastic collision?)

  2. jcsd
  3. Oct 18, 2008 #2


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    Staff: Mentor

    Yes. If the packet goes enters from the other direction, and goes from the "light" string to the "heavy" string, the reflected packet is inverted. I've done this as a demonstration in intro physics classes.

    You have something similar in optics. Light reflecting off a air-to-glass boundary (from outside the glass) is phase shifted by half a cycle, but not when reflecting off a glass-to-air boundary (from inside the glass). Here what matters is whether the index of refraction increases or decreases as you go across the boundary.
  4. Oct 18, 2008 #3
    thanks, I like the optics comparison, shall help me remember the order.
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