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Spin question

  1. Sep 8, 2009 #1
    My quantum knowledge is very minimum.
    If spin is +/-(1/2), then the proton has 2 energy levels. (for ex: hydrogen)

    So, if the spin is just 1/2, there is only one energy level, correct?
    Is this possible?
  2. jcsd
  3. Sep 8, 2009 #2


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    Staff: Mentor

    You're referring to two different quantum numbers, which are associated with different aspects of intrinsic angular momentum ("spin").

    In general, angular momentum is a vector quantity: it has both magnitude and direction (orientation). The quantum number [itex]s[/itex] is associated with the magnitude of the spin, which is always positive. For a proton (or neutron or electron, for that matter), [itex]s = 1/2[/itex]. The quantum number [itex]m_s[/itex] is associated with the direction (orientation) of the spin. With [itex]s = 1/2[/itex], we can have either [itex]m_s = +1/2[/itex] or [itex]m_s = -1/2[/itex] (often called "spin up" and "spin down"). When a particle is in a magnetic field, its energy depends on the value of [itex]m_s[/itex].
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