Critical angle and total internal reflectionEdexcel International A Level Physics: Mind map

Exam questions on Critical angle and total internal reflection

1. A ray of light travels inside a rectangular block of glass of refractive index 1.60 and strikes a flat glass–air boundary from inside the glass. Take the refractive index of air as 1.00.
   The block is now immersed in water of refractive index 1.33. Calculate the critical angle for the glass–water boundary.2 marks
2. A bare optical fibre made of glass with refractive index 1.52 is surrounded by air. Light signals travel along the fibre by repeatedly meeting the side wall of the fibre, which is a glass–air boundary.
   A ray inside the fibre meets the side wall at an angle of incidence of 38°. Determine whether the ray is totally internally reflected.2 marks
3. A small lamp is fixed at the bottom of a swimming pool, 2.0 m below the water surface, and shines light in all directions upwards. The refractive index of the water is 1.33 and that of air is 1.00. A swimmer looks at the surface from above.
   Calculate the critical angle for the water–air surface. Explain why light from the lamp that reaches the surface at an angle of incidence of 60° does not emerge into the air.3 marks