Critical Angle For Total Internal Reflection — the NEET Physics formula with its derivation, variables, validity constraints and worked solver.
Critical Angle for Total Internal Reflection Applies when light travels from a medium of higher refractive index to a medium of lower refractive index. Apply Snell's Law: n1 sin(θ1) = n2 sin(θ2) Substitute n1 = n (denser medium) and n2 = 1 (rarer medium) Set angle of refraction θ2 = 90 degrees for critical incidence Set θ1 = C (Critical Angle) n sin(C) = 1 sin(90) results in sin(C) = 1/n The rarer medium is assumed to be vacuum or air (n=1); otherwise use sin(C) = n2/n1. The angle of incidence must be in the optically denser medium. n must be greater than 1. Thinking TIR occurs when light travels from air to glass. Assuming the critical angle is the same for all colors (it depends on wavelength because refractive index depends on Cauchy's relation). Believing TIR occurs exactly at the critical angle; it starts when the incidence angle is strictly greater than the critical angle.