This lecture covers the electrical conductivity of metals, introducing concepts such as current density, electrical resistivity, and thermal conductivity. It explains the Drude model, the impact of impurities on conductivity, and the behavior of metals and semiconductors at different temperatures. The lecture also delves into the energy gap in semiconductors, the Boltzmann and Fermi-Dirac statistics, and the particle-wave duality of light in optical properties of semiconductors.