Aspin 1/2 particle is in an eigenstate of sa with eigeavalue h/2 at time t 0. at that time a uniform magnetic field of magnitude b pointing in the z-direction turns on. the particle is allowed to precess for a time t. at that instant, the magnctic field is rotated very rapidly, so that it now points in the y-direction. after another time interval t, a measurement of se is carried. what is the probability that the value h/2 will be found?