Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Potential Barrier (Q.M. vs Classical Phy.)

  1. Mar 16, 2007 #1
    If you have a Potential Barrier V (width a) and particles incident on left with energy E where E>V, are the following true:

    Classical Physics:
    - All particles will be transmitted past the barrier
    - It cannot be reflected because that would mean it has negative E which is not possible.

    Quantum Mecahnically:
    - Some particles will be reflected (due to there wave nature)
    - Some particles will be transmitted
    - Some particles may exist in the barrier
    - Resonant modes exist for 100% transmission of particles

    Am I missing anything important?
  2. jcsd
  3. Mar 21, 2007 #2
    In order:

    Classical Physics:
    - Yes
    - You are correct that it cannot be reflected in the case of E>V but this has nothing to do with negative energy, rather it is reflected if E<V. Moreover, you can have a negative energy if your potential is defined for negative values. (In fact, potentials are often defined such that bound states correspond to negative energies.)

    Quantum mechanically:
    - Yes
    - Yes
    - Yes, but only if E<V (the opposite of your stated case) and if your barrier is a well and not a step.
    - Not so sure about the resonant modes part.

    Now someone else can check to see if I missed anything important.
    Last edited: Mar 21, 2007
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook