What is Alpha?

 

  1. )   Spectroscopic quantity, (measure of doublet separation in hydrogen and other one electron atoms).

  2. )   Electromagnetic coupling constant, (characterizes the photon/electron interaction or the square of an effective charge screened by vacuum polarization and seen from an infinite distance).

  3. )   Dimensionless ratio of fundamental constants:
         1/137     e2/(4 0 c)
  4. )   Any of the above.

  5. )   All of the above.

  6. )   None of the above.

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