A student investigates the optical properties of a semicircular plastic block.
They direct a narrow ray of light into the block through the curved surface at point Y, as shown in the diagram. The ray travels straight through point Y without changing direction.
Which of these explains why the ray of light does not bend (refract) when it enters the plastic block at point Y?
The ray enters along a normal to the curved surface of the block.
The ray enters parallel to the plastic surface at point Y.
The ray speeds up as it enters the plastic.
There is no change in the speed of the ray as it enters the plastic.