In 1827, German scientist Georg Ohm published Ohm's law of constant electrical resistance in metals. Ohm's Law is one of the unbreakable rules of experience for nearly two centuries after its discovery. It was recently discovered that Ohm's law, which never seemed to be broken, was not established in BiSb alloys. The BiSb alloy whose energy band is twisted becomes a topological metal (Weyl metal) in the absence of time reversal symmetry. When an electric field is applied in a certain direction, some of the electrons move in the direction of the electric field without resistance. The density of electrons flowing without resistance changes with the applied electric field. As a result, no current flows in a Weyl metal in proportion to the applied voltage. Therefore, the resistance changes according to the voltage, that is, the metal does not satisfy Ohm's law. In this talk, we will look closely at the meaning of Ohm's law and share information on the principles and applications of nonohmic conductance.