What is the key optical principle behind the working of a periscope?
**TIR application** requires n₁>n₂ and θ₁>C. Critical angle formula derived from Snell's law with θ₂=90°, n₁ sinC = n₂ sin90° = n₂, so sinC = n₂/n₁. For glass-air sinC=1/1.52, C≈41°, for water-air 48.6°, determining cutoff for transmission. A periscope uses total internal reflection in prisms (or plane mirror reflection) to redirect light. Prisms reflect light internally at angles greater than the critical angle, allowing the viewer to see objects from a different height or direction without direct line-of-sight. Substituting values gives Total internal reflection in prisms, which matches expe
Ref: NCERT > Physics Book > Ray Optics > Total Internal Reflection and Critical Angle