This lecture covers the applications of polarizers in various fields such as geology, astronomy, and technology, including 3D film, sunglasses, LCD screens, and radio transmission. It explains the behavior of electromagnetic waves in anisotropic mediums, the concept of birefringence in crystals, and the phenomenon of double refraction. The lecture also delves into the optical properties of anisotropic crystals, the separation of light waves, and the effects of different orientations with respect to the crystalline optical axis.