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Homework Help: Potential barriers, etc.

  1. Nov 16, 2006 #1
    New some help with some problems. I have tried them an listed what I have done so far...

    1. A beam of electrons is sent along the x axis from - with kinetic energy E=7.5eV. The beam encounters a potential barrier of height V'=1eV and width 2a=1.2nm.
    What fraction of the incident beam is reflected? [Hint: Assume E>>V0]
    I found k and q and from these found |R|^2, but have had no success in getting the correct answer. Am I supposed to do something after I find |R|^2?

    2. Suppose a wave function within a barrier is approximately proportional to e-kx. The
    probability that a particle will penetrate a barrier of thickness 2a is 0.010. What is the
    probability of penetrating a barrier that is twice as thick?
    Not even sure where to start here... I know that my thickness will now be 4a, but what now?

    3. Suppose electrons with E= 10.0 eV approach a potential barrier of height 2.0 eV.
    a. Suppose electrons with E= 10.0 eV approach a potential barrier of height 2.0 eV. in nanometers

    b. For what minimum barrier thickness is there no reflection? in nanometers
    Not sure where to start. I think i need to solve for 2aq=n*pi for a and for b where n*pi/2.

    I am not really looking for the answers, but how to solve them as there is not much help in the text.

    Thanks in advance.
  2. jcsd
  3. Nov 17, 2006 #2
    Can you show us your work on question 1?
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