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Homework Help: Tunneling at potential step

  1. Mar 22, 2013 #1
    1. The problem statement, all variables and given/known data

    A beam of particles of energy E = 9 eV strikes on a step potential and 25% of the beam's particles is reflected back. What is the height of the step potential?

    (A) 4 eV
    (B) 8 eV
    (C) 3 eV
    (D) 1 eV
    (E) 5 eV

    2. Relevant equations

    √(R) = [√(E)-√(E-U)]/[√(E)-√(E_U)]

    3. The attempt at a solution

    Just plug and chug the equation I have, but this is for a timed test without a calculator or equation sheet. This seems clunky to remember, solve and do in such conditions. Is there a simpler way? I get 8eV, which is the correct answer.
  2. jcsd
  3. Mar 23, 2013 #2


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    2017 Award

    Staff: Mentor

    You can remember that you need a significant potential step to get significant reflection.
    Estimate reflection for 5 eV, if the value is too low, it has to be 8 eV.

    Is there a sign error in your formula?
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