Problem 5.198

A tube of length \(l=26 \mathrm{~cm}\) is filled with benzene and placed in a longitudinal magnetic field of a solenoid positioned between two Polaroids. The angle between the principle directions of the Polaroids is equal to \(45^{\circ} .\) Find the minimum strength of the magnetic field at which light of the wavelength \(589 \mathrm{nm}\) propagates through that system only in one direction (optical valve). What happens if the direction of the given magnetic field is changed to the opposite one?