Total internal reflection occurs in an optical prism when light rays

Total internal reflection occurs in an optical prism when light rays are incident in the prism at an angle greater than the critical angle. When a light ray travels from an optically denser medium (like a glass prism) to a less dense medium (like air), it bends away from the normal line. As the angle of incidence increases, the angle of refraction also increases until it reaches a certain angle called the critical angle. If the angle of incidence is greater than the critical angle, the light ray is totally reflected back into the denser medium, which is known as total internal reflection. This phenomenon is used in various optical devices such as prisms, optical fibers, and reflecting telescopes.