The Hamiltonian for a spin-1/2 particle in a magnetic field B = B0\(\hat{k}\) is given by H = λ S ⋅ B, where S is its spin (in units of h) and λ is a constant. If the average spin density is (S) for an ensemble of such non interacting particles, then \(\frac{d}{dt}\) 〈Sx〉
1
\(\frac{\lambda}{h}B_0\langle S_x\rangle\)
2
\(\frac{\lambda}{h}B_0\langle S_y\rangle\)
3
\(-\frac{\lambda}{h}B_0\langle S_x\rangle\)
4
\(-\frac{\lambda}{h}B_0\langle S_y\rangle\)