Question

Consider a system of three non-interacting spins in equilibrium with a magnetic field H (this system is not really macroscopic, but is illustrative). Each spin can have only two possible orientations: parallel to H, with magnetic moment u and energy (-u H), or antiparallel with magnetic moment -u and energy (uH).
a) List and identify all possible states of the system.
b) If it is known that the system has an energy (-uH):
i. What are the accessible states?
ii. What is the probability that the first spin is parallel to the field?
iii. What is the average magnetic moment of that spin?

Answer 1