What optical property of a prism allows it to be used in binoculars to invert images?
**Critical angle** C satisfies sinC = n₂/n₁, n₁>n₂, n₂=1 for air, n₁=1.52 for glass gives sinC=1/1.52=0.6579, C≈41.1°, for water n=1.33 C=48.75°. Beyond C, total internal reflection occurs, all light reflected, no refracted ray, used in optical fibers and prisms. Prisms in binoculars use total internal reflection to invert and revert images. By reflecting light multiple times within the prism (e.g., in a Porro prism), the image orientation is corrected from the inverted form produced by the objective lens, maintaining the same size. Substituting values gives Total internal reflection, which ma
Ref: NCERT > Physics Book > Ray Optics > Total Internal Reflection and Critical Angle