A parallel beam of light is incident on a spherical drop of water `(mu = 4//3)`. Consider refraction of light at air-water interface, then reflection at water-air boundary (of course there will be refracted light energy in air as well), followed by refraction at water-air interface. Path of a typical ray refracted at A, then reflected at B and finally refracted at C has been shown in the Figure. Find the maximum value of angle `delta`. use `sin^(-1) sqrt((20)/(27)) = 60^(@)` and `sin^(-1) sqrt((5)/(12)) = 40^(@)`.

Answer

`40^(@)`