Explain what happens to a ray of light when it travels from air into a glass block at an angle to the normal, and then exits the glass block back into air.

Eduqas A-Level Physics — 2.6 Refraction of light · Explain · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

A ray of light travels from air and strikes the surface of a glass block at an angle to the normal. The ray passes through the glass and emerges from the other side back into air.

Model answer (5 marks)

The ray slows down as it enters the glass, so it bends towards the normal – this change in direction is called refraction. When it reaches the other face it speeds up again and bends away from the normal as it exits back into air.

Examiner tips

Use the word "refraction" to link the change in speed and direction.
Show the sequence: slow → bend towards normal → fast → bend away from normal.
Mention the medium change (air to glass, glass to air).

Common mistakes

Forgetting to state that the ray bends towards the normal when entering.
Confusing the direction of bending on exit – it should be away from the normal.

Mark scheme (5 marks)

The ray slows down as it enters the glass
The ray bends towards the normal when entering the glass
This change in direction is called refraction
The ray speeds up again as it exits the glass back into air
The ray bends away from the normal when exiting the glass into air

Key terms in this question

normal