- #1
barefeet
- 59
- 2
Homework Statement
Using
[tex]
J^2 \mid j,m_z \rangle = h^2 j(j+1) \mid j,m_z \rangle
[/tex]
[tex]
J_z \mid j,m_z \rangle = hm_z \mid j,m_z \rangle
[/tex]
Derive that :
[tex]
\langle j,m_z \mid J_-J_+ \mid j,m_z \rangle = h^2[ j(j+1) - m_z(m_z+1)]
[/tex]
Homework Equations
[tex]
J_- = J_x - iJ_y
[/tex]
[tex]
J_+ = J_x + iJ_y
[/tex]
The Attempt at a Solution
[tex]
J_-J_+ = (J_x- iJ_y)(J_x + iJ_y) = J_x^2 + J_y^2 = J^2 - J_z^2
[/tex]
[tex]
\langle j,m_z \mid J_-J_+ \mid j,m_z \rangle = \langle j,m_z \mid J^2 - J_z^2 \mid j,m_z \rangle = h^2[ j(j+1) - m_z^2]
[/tex]
Apparently I am missing a term here but I don't know where it should come from. I thought this should be true
[tex]
J_z^2 \mid j,m_z \rangle = J_zJ_z \mid j,m_z \rangle = h^2m_z^2 \mid j,m_z \rangle
[/tex]
(Note: h is hbar everywhere )