Refraction
4 marks · NormalA student shining a light ray into water measures the following angles for different boundaries:
| Boundary | Angle of Incidence | Angle of Refraction |
|---|---|---|
| Air-water | 40° | 28° |
| Water-glass | 30° | 22° |
For the air-water boundary, is the light bending towards or away from the normal? Explain.
For the water-glass boundary, which medium is slower for light: water or glass? Justify your answer using the angles.
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(a) The light is bending towards the normal because the angle of refraction (28°) is less than the angle of incidence (40°). · must show Compares angles, Identifies direction relative to normal
(b) Glass is slower for light. The angle of refraction in glass is less than in water (22° vs 30°), so light slows down entering glass. · must show Angle of refraction smaller, Correctly identifies the slower medium
Common mistakes: Incorrect interpretation of larger/smaller angles; Forgetting angles are measured to the normal
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Correctly states the direction of bending (towards normal)
B1 (a) · 1 mark · Supports answer by comparing the angles
B1 (b) · 1 mark · Correctly identifies glass as slower for light
B1 (b) · 1 mark · Uses the angles to justify answer
Worked solution
(a) The light bends towards the normal because the angle of refraction (28°) is less than the angle of incidence (40°).
(b) Glass is slower for light than water because the light bends further towards the normal: its angle of refraction is smaller (22° vs 30°) when entering glass.