Refraction is when a wave changes direction as it crosses from one material into another. Most students know that. But when an exam asks you to explain it, a one-line answer won’t get the marks.
Towards or away?
- Wave slows down (air → glass): bends towards the normal.
- Wave speeds up (glass → air): bends away from the normal.
- Travelling along the normal: changes speed but not direction.
The full-marks explanation (Higher)
Examiners’ reports say that just writing “light slows down in glass” earns 1 mark at most. For full marks, use wavefronts:
“One side of the wavefront reaches the glass first and slows down, while the other side is still travelling faster in air. This makes the wavefront turn, so the wave changes direction.”
What stays the same?
When a wave refracts, its speed and wavelength change but its frequency stays the same. So if you know the new speed, you can use v = fλ to find the new wavelength.
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