A ray of light passes from glass (\( n = 1.52 \)) to air at an angle of incidence of \( 45^\circ \). What happens?
**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. Critical angle: sin i_c = (n₂/n₁) = (1/1.52) ≈ 0.658 ⇒ i_c ≈ 41.1° . Since i = 45° > i_c , total internal reflection occurs. Substituting values gives Total internal reflection, which matches expected image position and magnification from mirror/lens formula 1/f = 1/v - 1/u (lens) or 1/f = 1/v + 1/u (mirror), confirming sign conventions and refraction principles.
Ref: NCERT > Physics Book > Ray Optics > Total Internal Reflection and Critical Angle