The device used to measure resistance in electrical circuits is called an ohmmeter. While a multimeter can measure voltage and current, an ohmmeter specifically focuses on resistance. It operates using Ohm's Law, which involves calculating resistance through the formula R = V/I. The discussion also highlights that the resistance of a wire is influenced by its length, cross-sectional area, and material properties, with mass affecting resistance indirectly. Additionally, the efficiency of electron movement in metals compared to nonmetals is attributed to the internal structure of the materials, which is explained by concepts in Quantum Mechanics and Transport Phenomena. Lastly, it is clarified that an ohmmeter requires power to function and measure resistance accurately.