Explain what happens to the speed, wavelength, and direction of a monochromatic ray of light as it passes from glass into air.

AQA A-Level Physics (7408) — 3.3.2 Refraction, Diffraction and Interference · Explain · 5 marks · View as Markdown

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

A ray of monochromatic light travels from glass into air, crossing the boundary between the two materials.

Model answer (5 marks)

The speed of light increases when it moves from glass into air.
The wavelength increases in air.
The frequency remains unchanged.
The ray bends away from the normal as it enters the less dense material.
Air is less dense than glass, so the wave speeds up at the boundary, causing the change in direction.

Examiner tips

  • Use the word "bends" and mention the normal. State that the frequency is constant. Show the relationship between speed, wavelength and frequency (v=λf).
  • Mention the density difference to justify the direction change.

Common mistakes

  • Saying the ray bends towards the normal. Confusing speed with frequency. Forgetting to state that the frequency does not change.

Mark scheme (5 marks)

  1. The speed of light increases as it moves from glass into air
  2. The wavelength increases as the light enters air
  3. The frequency remains unchanged / stays constant
  4. The ray bends away from the normal as it enters the less dense material
  5. Air is less dense than glass, so the ray changes direction because the wave speeds up at the boundary

Key terms in this question

wavelength

Related

More Refraction, Diffraction and Interference questions

▶ Try answering this question with AI marking (free) →