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If $\vec{\alpha}$ is a vector $(\alpha_1,\alpha_2,\alpha_3)$, show that  $$ (\vec{\alpha}\cdot\vec{\sigma})^2 = |\vec{\alpha}|^2$$  where \(|\alpha|=\sqrt{\alpha_1^2+\alpha_2^2+\alpha_3^2}\)  Use this result and show that \[\exp(i\vec{\alpha}\cdot\vec{\sigma}) =
\cos{|\vec{\alpha}|} + i\vec{\alpha}\cdot\sigma \sin|\vec{\alpha}|\]

kapoor kapoor's picture 28/10/18


Show that the Pauli matrices anti-commute. $$\sigma_j\sigma_k + \sigma_k\sigma_j  =2\delta_{jk}$$ and that the square of each Pauli matrix is identity matrix. $$\sigma_k^2=I, \qquad k=1,2,3$$

kapoor kapoor's picture 28/10/18


Show that for a system of two identical particles having spin $s$, the ratio of the number of states, symmetric under exchange of spins, to the number of the antisymmetric states is given by ${(s+1)\over s}.$

kapoor kapoor's picture 28/10/18

QM-20 :: Spin and Identical Particles

Summary (or abstract) not available for this node.
kapoor kapoor's picture 28/10/18


Prove that the Pauli matrices satisfy the commutation relations.
 $$    [\sigma_i,\sigma_j]=2i\epsilon_{ijk}\sigma_k  $$

kapoor kapoor's picture 28/10/18


Construct spin matrices for spin $3/2$. Using your answer find the matrix for $\vec{S}^2$. Do you need to construct all the three spin matrices to get an answer for $\vec{S}^2$?

kapoor kapoor's picture 28/10/18


  1. Using the known results for H- atom, write the wave functions for electron in Hydrogen atom for the following quantum numbers 
    (i) $ n=2 , \ l=1,\ m_l=1,0,-1$ 
    (ii) $n=2, \ l=2, m_l=2,1,0,-1,-2$.
  2. Write the wave function for an electron in a state with $j={1\over 2}, \ m_j= {1\over 2}$
kapoor kapoor's picture 28/10/18


Find the spin wave functions for a spin $1/2$ particle with spin projections $\pm 1/2$ along $(1,1,1)$. Verify that the two wave functions are orthogonal.

kapoor kapoor's picture 28/10/18


For an electron with $\ell=1$ what are the allowed values of the total angular momentum ? Write the total angular momentum states $\vert{jm}\rangle $ in terms of  $\vert{\ell=1\,m_l,~s=\frac{1}{2}\, m_s}\rangle$ states for all possible values of $j,m$.

kapoor kapoor's picture 28/10/18


Consider two  particles, $A,B$ each having spin 1. Construct all possible states $\vert{SM}\rangle$ with definite values of $S^2$ and $S_z$. Use the notation $\vert{A  m_1}\rangle\vert{B    m_2}\rangle$ to represent the states of the two particles having definite $z-$ projections $m_1,m_2$ of spin. Verify that the states are symmetric under exchange of $m_1$ and $m_2$ when total spin is $S=2,0$ and antisymmetric for $S=1$.

kapoor kapoor's picture 28/10/18