Kohler's Law

a semiempirical law that asserts that the relative change in the resistance ρ of a metal in a magnetic field H, which is dependent on many factors (temperature, impurities), can be expressed as a function of a single quantity H_eff = H(p₃₀₀/p), where ρ is the resistance of the conductor in the absence of the field and p3oo is the resistance in the field at room temperature (300°K). Kohler’s law permits data on the dependence of the resistance ρ on the field H for different samples of a single metal to be represented as a single curve. The expression was first established by the German physicist M. Kohler in 1938.

Since H_eff ∼l/r_H (where l is the mean free path and r_H is the mean radius of an electron’s orbit in the magnetic field), Kohler’s law indicates that the chief cause of changes in resistance in a magnetic field is the revolution of electrons about the magnetic field lines. Deviations from Kohler’s law, which are observed mainly in single-crystal metal samples, have been explained by the modern theory of galvanomagnetic phenomena.