GCSE questions on refraction and TIR

Q6. Katrina investigates how light travels in a semi-circular glass block.

The student shines a ray of light into a semi-circular glass block from three different directions as shown in the diagram below.

(a) Why does the ray not change direction on entering the semicircular block in any of the diagrams?

[1 mark]

(b) What is the name of the process that causes the light ray to change direction as it leaves the glass block in diagram Z?

[1 mark]

(d) Which angle, A, B or C, is the critical angle of the light in the block?

[1 mark]

(Total 4 marks)