A diver in a swimming poole wants to signal his distress to a person lying on the edge of the pool by flashing his water proof flash light

Options

A. He must direct the beam vertically upwards
B. He has to direct the beam horizontally
C. He has to direct the beam at an angle to the vertical which is slightly less than the critical angle of incidence for total internal reflection
D. He has to direct the beam at an angle to the vertical which is slightly more than the critical angle of incidence for the total internal reflection

Answer

C