4 The diagram shows a cube of glass. A ray of light, incident at the centre of a face of the cube, at an angle of incidence 8, goes on to meet another face at an angle of incidence of 50, as shown in Figure 3. critical angle at the glass-air boundary = 45 50 Figure 3 (a) Draw on the diagram the continuation of the path of the ray, showing it passing through the glass and out into the air. (3 marks) (b) Show that the refractive index of the glass is 1.41. (c) Calculate the angle of incidence, 0. air glass (2 marks) (3 marks)