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Homework Help: Problem about uncertainty principle

  1. Apr 17, 2013 #1
    We have an electron pulse of width 1 nanosecond and with kinetic energy of 1keV. We have to calculate Δx and Δp.

    I have a question regarding this problem. If they give us the kinetic energy of the electron pulse then we know exactly the momentum right? And so the uncertainty of momentum would be 0 and therefore Δx=∞ for the uncertainty principle ΔxΔp≥h. However I feel this reasoning is incorrect otherwise the problem would be trivial.
     
  2. jcsd
  3. Apr 17, 2013 #2

    mfb

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    The momentum, together with the energy, have some small uncertainty (<<1 keV). You can calculate the minimal uncertainty of this, based on the position uncertainty.
     
  4. Apr 17, 2013 #3
    And how do I calculate the position uncertainty? Both Δx and Δ p are unkown.
     
  5. Apr 17, 2013 #4

    mfb

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    Δx is known. It is hidden in the "length" of 1ns, and you can calculate the velocity.
     
  6. Apr 19, 2013 #5
    Thank you I finally solved I didn't understand the meaning of that 1ns.
     
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