Consider an Ising model in the presence of an external magnetic field B, which gives each dipole an additional energy of −μBB if it points up and +μBB if it points down (where μB is the dipole's magnetic moment). Analyze this system using the mean field approximation to find the analogue of equation 8.50. Study the solutions of the equation graphically, and discuss the magnetization of this system as a function of both the external field strength and the temperature. Sketch the region in the T-B plane for which the equation has three solutions.