Suppose That at Time $t=0$ An Electron in a Magnetic Field in The

Multiple Choice

Suppose that at time $t=0$ an electron in a magnetic field in the $+z$ direction has state $|\psi(0) \rangle=|+x\rangle$ . Let $\omega=\left[E_{+}-E_{-}\right] / \hbar$ .
-(a) The expectation value $\left\langle s_{z}\right\rangle$ as a function of time in this case is which of the below?

A) $+\frac{1}{2} \hbar$
B) $-\frac{1}{2} \hbar$
C) 0
D) $+\frac{1}{2} \hbar \cos \omega t$
E) $+\frac{1}{2} \hbar \sin \omega t$
F) Something else (specify)