Total Internal Reflection When light travels between mediums, some light is reflected and some is refracted Light bends away from the normal when it speeds up at the boundary of two media Angle of refraction is larger than the angle of incidence

Critical Angle The angle of refraction continues to increase as the angle of incidence increases. Eventually, the angle of refraction will become 90º At this point, the angle of incidence is called the CRITICAL ANGLE

It’s Trapped! Click HERE If the angle of incidence is increases past the critical angle, the refracted ray will not exit the medium It will reflect back into the medium This is called TOTAL INTERNAL REFLECTION Click HERE

Conditions for TIR Total internal reflection occurs when 2 conditions are met: Light is travelling more slowly in the first medium than in the second The angle of incidence is larger than the critical angle

Calculating Critical Angle Calculate the critical angle for a water air boundary. n1=1.33 n2=1.00 Θ2 = 90º θ1 = ? n1sin(θ1) = n2sin(θ2) sin(θ1) = n2sin(θ2) n1 sin(θ1) = (1.00)sin90 1.33 sin(θ1) = 0.75 θ1 = sin-1(0.75) θ1 = 49° The critical angle of the water air boundary is 49 °