Light enters a solid tube made of plastic having an index of refraction of 1.69. The light travels parallel to the upper part of the tube. (See the figure .) You want to cut the face AB so that all the light will reflect back into the tube after it first strikes that face.
Hello The angle for total internal reflection is Θc = arcsin(n2/n1) in the case where n2 = 1 (air) Θc = arcsin(1/1.69) = 36.27° -- ans. this is the angle with the normal of the surface. The angle that you are asking for is 90°-Θc = 53.73° ---------- in the case where n2 = 1.333 (water) Θc = arcsin(1.333/1.69) = 52.06° and Θ = 90 - 52.06 = 37.94° -- ans. Regards
