Refraction and total internal reflection — final check

1. define / describe / calculate

(a) Define the angle of incidence. (b) A pupil shows refraction with two transparent blocks on paper: a rectangular glass block and a triangular glass prism. Describe how she records the direction of the ray that leaves each block, and how that ray compares with the ray that went in, for each shape. (c) Supplement. Define refractive index in terms of the speed of light. (d) Supplement. A ray in air meets a transparent crystal with an angle of incidence of 43°. The angle of refraction is 26°. Calculate the refractive index of the crystal.

(a) The angle of incidence

(b) The rays out of the two blocks

(c) Supplement: refractive index

(d) Supplement: the refractive index here

2. describe / identify / calculate

(a) Light that has entered a glass bead on a necklace meets the far surface of the bead from inside, with an angle of incidence smaller than the critical angle. Describe what happens to the light at that surface. (b) Another ray inside the bead meets the surface at exactly the critical angle. Describe the ray that comes out into the air. (c) A third ray meets the surface at more than the critical angle. Describe what happens to it, and identify one device that uses this effect. (d) Supplement. The glass of an optical fibre is silica, with a refractive index of 1.46. Calculate its critical angle. (e) Supplement. Telephone calls cross the ocean along optical fibres. Describe the form a call takes inside the fibre, and what happens to it at the far end.

(a) Below the critical angle

(b) At the critical angle

(c) Above the critical angle

(d) Supplement: the critical angle of silica

(e) Supplement: a call in a fibre