In a rectangular cuvette, two opposite walls of which are metal, and the rest are made of an insulator, an electrolyte is poured, the density of which is ρ, the specific conductivity is λ. A voltage V is applied to the metal walls of the cuvette, and the entire cuvette is placed in a uniform vertical magnetic field of induction B. Determine the difference in liquid levels near the non-metallic walls of the cuvette. Cuvette length a, width b.